Showing posts with label bacteria. Show all posts
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10:52 PM
The domain Archaea represents a diverse group of prokaryotes originally found in environments once considered to be hostile to life, now known to be widely distributed in nature.

The cycling of plant nutrients, such as carbon, nitrogen, and sulfur, requires the activity of microorganisms that convert these elements to forms readily available to plants. These microorganisms, which are generally found in both soil and water, include both prokaryotic organisms of the domain Bacteria and the domain of prokaryotes called Archaea, which play significant roles in nutrient cycling.

Along with Eukarya, to which protists, fungi, plants, and animals belong, the Archaea formone of the three domains of life. The Archaea are related to both Bacteria and Eukarya and, in some respects, appear to bemore closely related to Eukarya.

Biochemical and genetic studies, including information obtained from whole genome sequencing, suggest that Archaea may be closely related to an ancestor that gave rise to both Bacteria and Eukarya. Thus, Archaea may provide some insight into the processes that resulted in the evolution of higher life-forms, including plants and animals.


A Third Domain

For more than fifty years, biologists categorized living organisms into two groups based on their cellular organization and complexity: prokaryotes (originally all classified in kingdom Monera), the single-celled organisms whose chromosomes are not compartmentalized inside a nucleus (which include the domainBacteria), and eukaryotes, consisting of all other organisms, whose cells contain a nucleus. In the late 1970’s studies on a unique group of microorganisms led investigators to question the accepted classification of prokaryotes.

Originally called Archaebacteria by molecular biologist Carl Woese and his colleagues in 1977, these microorganisms were isolated from environments characterized by extremes in heat, acidity, pressure, or salinity, and many were found to be able to utilize sulfur and molecular hydrogen as part of their growth process.

Like all prokaryotes, Archaea do not have a nucleus. However, in their biochemistry and the structure and composition of their molecular machinery, they are as different from bacteria as they are from eukaryotes.

Woese and his colleagues analyzed and compared specific molecules of ribonucleic acid (RNA) present within the ribosome in all organisms, called ribosomal RNA (rRNA). Their findings suggested that all extant life is composed of three distinct groups of organisms: the eukaryotes, or domain Eukarya, which includes plants and animals, and two different prokaryotes, domains Bacteria and Archaea.

In 1990 Woese and others recommended the replacement of the simple prokaryote/ eukaryote view of life with a new tripartite scheme based on three domains: the Bacteria, Archaea, and Eukarya. Since 1990 the three-domain classification has been the subject of considerable debate, and as a consequence, both old and new terminology are used in scientific and popular literature.

Characteristics

Generally, the size and shape of Archaea are similar to those of Bacteria. They are single-celled microscopic organisms that, in some cases, are motile (capable of self-movement) and may be found in chains or clusters.

Archaea multiply in the same manner as bacteria: via binary fission, budding, or fragmentation. Like Bacteria, archaeal chromosomes are circular, indicating the absence of breaks or discontinuities, and many genes are organized in the same fashion as those found in Bacteria.

On the other hand, the specific chemical composition of Archaea plasma membranes and cell walls is unique to the Archaea and is quite different from the composition of these structures typically found in either Bacteria or Eukarya. In fact, the distinctive ether-linked isoprenoid lipids that compose the external membranes of Archaea are a hallmark of these microorganisms.

Another unique characteristic of Archaea is the composition of the molecular genetic machinery, which is amosaic of the components found in Bacteria and Eukarya. For example, the ribosomes (which are responsible for protein synthesis) of Archaea resemble the ribosomes of Bacteria in shape and composition and are distinct from the ribosomes of Eukarya.

On the other hand, the enzyme utilized by Archaea in the production of RNA, namely RNA polymerase, is quite different from the enzyme found in Bacteria. In Bacteria, RNA polymerase molecules are composed of four major proteins, while in the Archaea, RNA polymerase molecules consist of more than ten proteins and are surprisingly similar to the enzyme found in Eukarya.

In fact, archaeal RNA polymerase is so similar to the eukaryotic enzyme that combining certain proteins from both archaeal and eukaryotic sources results in a functional enzyme, a manipulation that is not possible with any bacterial RNA polymerases.

Among species of the Archaea, there is a variety of metabolic processes that differ greatly from the better-known metabolic routes of Bacteria and Eukarya. Many of the archaeal pathways used to convert food sources to energy and building blocks for growth involve enzymes having biological activities not found in any other biological systems.

In some cases, the enzymes require the involvement of rare metals, such as tungsten. While a requirement for metals in the activity of many bacterial and eukaryotic enzymes is ubiquitous, the use of tungsten appears to be unique to Archaea.

Diversity

A fascinating feature of Archaea is that they are found in niches that support the growth of few other organisms. These include highly reduced (oxygen-free) environments or very high-temperature environments found near hot springs or undersea hydrothermal vents as well as sites that are sulfur-rich and highly acidic.

Archaea are also found in highly saline marine environments and hypersaline lakes where the salinity is as much as ten times that in seawater. Based on the comparison of ribosomal RNA sequences as well as physiological and metabolic characteristics, the Archaea have been divided into three subdomains: Euryarchaeota, Crenarchaeota, and Korarchaeota.

The Euryarchaeota includes members of the methanogenic (methane-producing) and halophilic (salt-requiring) Archaea as well as many that grow at very high temperature, the thermophilic and extremely thermophilic, or hyperthermophilic, Archaea.

Representatives of hyperthermophilic Archaea are found in the Crenarchaeota, which also includes cold-dwelling Archaea that have been isolated in association with certain marine sponges. The Korarchaeota also includes hyperthermophilic Archaea, although these were not isolated or characterized as of 2001, but whose presence in hot spring and deep-sea samples has been identified by molecular biological techniques.

Methanogenic Archaea

Methane-producing Archaea are found in strictly anaerobic environments. They have no tolerance for oxygen: Trace amounts are inhibitory for growth, and too much is lethal. These Archaea obtain energy for growth by a process called methanogenesis, which results in the conversion of carbon dioxide to methane gas.

Methane production requires several enzymes that use coenzymes unique to methanogenic Archaea. The production of methane is of great importance to carbon cycling inmany anaerobic environments, and microorganisms that produce this gas have been known for centuries.

In 1776 the scientist Alessandro Volta demonstrated that air generated from sediments rich in decaying vegetation, such as those present in bogs, streams, and lakes, could be ignited. It is now known that methanogenic Archaea are responsible for generating this "marsh gas".

Because methanogens require an oxygen-free environment for growth, they are found onlywhere carbon dioxide and hydrogen are available and oxygen has been excluded. Thus, methanogens thrive in stagnant water, natural wetlands, paddy fields, and in the rumen of cattle and other ruminants as well as in the intestinal tracts of animals and the hindguts of cellulose-digesting insects, such as termites.

Methanogens are also found in hot springs and the deep ocean and are major components of the anaerobic process in waste treatment facilities. It has been estimated that production of methane by themethanogenicArchaeamay account for almost 90 percent of the total methane released into the atmosphere each year.

In addition to playing a role in carbon cycling, several methanogenic Archaea are also involved in nitrogen cycling, as they are able to convert molecular nitrogen into organic nitrogen via nitrogen fixation, a process that is shared by only a few prokaryotes.

Thermophilic Archaea

Thermophilic Archaea live in environments ranging in temperature from55 degrees Celsius (131 degrees Fahrenheit) to 80 degreesCelsius (176 degrees Fahrenheit). Hyperthermophilic Archaea grow at temperatures near or greater than the boiling point ofwater and as high as 113 degrees Celsius (235 degrees Fahrenheit).

These Archaea have been isolated from hot sulfur springs, sulfur-laden mud at the base of volcanoes, and near very hot deep-sea hydrothermal vents where super heated water is emitted at very high temperatures under pressure.

Species that can use oxygen, as well as those that have no tolerance for oxygen, are known. Many of the anaerobic representatives obtain energy for growth by the metabolism of elemental sulfur.

In addition, many are found in environments that are extremely acidic, including those that are members of Thermoplasmatales. This group is noted for its ability to growat a pHof 2.0 and below(on a scale where pH 7.0 is neutral), which is equivalent to the acid in car batteries.

Arepresentative is Thermoplasma, which does not possess a cell wall but has a chemically unique structure composed of a lipid-polysaccharide (tetraether lipid with mannose and glucose units) that is distinctly different from the unusual ether-linked lipids found in the membrane components of typical Archaea.

Halophilic Archaea

The salt-dependent halophilic Archaea require extremely high concentrations of salt for survival, and some grow readily in saturated brine, where the salt concentration reaches 32 percent (in seawater it is approximately 3.5 percent) and where very alkaline conditions are not uncommon. Halophilic Archaea are found in salty habitats along ocean borders and inland waters such as the Dead Sea and the Great Salt Lake.

The reddish-purple color observed in salt evaporation ponds is due to production of red- and orange-colored carotenoids and other pigments associated with the massive growth of halophilic Archaea.

Some halophilic Archaea are capable of harvesting light to provide energy for growth by a mechanism that does not involve chlorophyll pigments. Light harvesting by these halophilicArchaea is done by a membrane-bound protein called bacteriorhodopsin that is equivalent to the mammalian eye pigment rhodopsin in both function and structure.

Bacteriorhodopsin contains retinal, a purple carotenoid like molecule used for light trapping. Interestingly, retinal is produced via a pathway that contains many of the same enzymes used for the production of lycopene by tomatoes during ripening.

Window to the Past

The extreme conditions in which Archaea are found suggests that these organisms have adapted to environments thought to exist during early life on earth, three billion to four billion years ago. Thus, the Archaea might be considered as a window into the past, and they may shed light on the processes involved in evolution as well as their relationships with Bacteria and Eukarya.

In order to survive in their unique environments, Archaea possess molecules that withstand heat or cold, acids, salt, and in some cases, pressure—characteristics that are tailor-made for specific applications inmolecular biology and biotechnology.

Uses

A number of important applications have been developed as a consequence of studying the Archaea. These include the identification of heat stable enzymes for analyses used in genetic fingerprinting and cancer detection (certain polymerase chain reaction enzymes), the use of halophilic pigments for holographic applications, optical signal processing and photoelectric devices, and methanogenesis as an alternative fuel source.
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6:17 PM
Bacterial Genetics
Bacterial Genetics
Bacterial genetics is the study of the genetic material of bacterial DNA, which can provide valuable insights into the process of mutation because of bacteria’s rapid rate of reproduction.

Plants were the original candidates for genetic studies, which began in the late 1800’s. Studies with animals soon followed; bacteria did not become candidates for such study until the mid-1940’s, when adequate technology for handling bacteria developed. Bacteria have become extremely useful organisms for genetic studies since the early 1950’s.

Two major features of bacteria make them desirable subjects. First, bacterial cells typically divide every twenty minutes. Their rapid rate of reproduction allows a very large number of bacteria to be produced in a short time. This, in turn, provides the researcher with more opportunity to detect the "rare genetic events" of mutation or recombination.

Even more important, unlike all other organisms, bacteria have a single chromosome with a single set of genes. Thus, genetic modifications are more likely to result in immediately observable changes. In organisms that have multiple chromosomes, a change in a single gene may go undetected because its effect is masked by genes on other chromosomes.


Bacterial DNA

All bacteria have a single circular chromosome, composed of deoxyribonucleic acid (DNA). The DNA is subdivided into specific message areas known as genes, and the chromosome carries from four thousand to five thousand individual genes. For many bacteria, this constitutes the entirety of its genetic information.

A number of bacteria, however, have additional DNA in the form of plasmids. A plasmid is a small additional circular piece of DNA, independent of the chromosome,which can hold an additional twenty to one hundred genes. Plasmid-containing cells often have several plasmids.

Many researchers have described the plasmid genes as nonessential to the normal activities of bacteria. Under certain circumstances, however, those genes might provide a survival advantage to the possessor. For example, genes for antibiotic resistance are often carried on a plasmid.

Normally, antibiotics are not present in the bacteria’s environment; such resistance genes would therefore be unnecessary. If the bacteria later were to come into contact with antibiotics, however, having antibiotic- resistant genes would be to their distinct advantage.

Two major types of plasmids exist: F plasmids, or fertility plasmids, and R plasmids, or resistance plasmids. Both types can carry resistance genes. Only the F plasmids, however, are able to control the formation of a special cytoplasmic tube known as the sex pilus. Cells with the F plasmids are known as F+, or donor cells. Cells without the F plasmids are called F-, or recipient cells.

Conjugation

Conjugation
Conjugation

The plasmid is a prerequisite to one type of genetic exchange, conjugation. During conjugation, the donor cell copies its plasmids and transfers them to a recipient cell to which it has attached itself by means of a sex pilus.

The recipient cell can now take advantage of whatever additional genes it has received. If, in the process, it received an F plasmid, it has also become a potential donor cell.Whenever bacterial cells undergo cell division, any plasmids they possess are typically passed on to their progeny.

Originally it was thought that conjugation could occur only between members of the same species, but that is not always true. For example, it is now known that some strains of the bacteria responsible for causing gonorrhea, Neisseria gonorrhoeae, have received antibiotic-resistant genes from unrelated species of bacteria.

There is one other type of donor cell, the Hfr+, or high-frequency recombinant, cell. Instead of the plasmid remaining independent of the cell’s chromosome, it inserts itself into the chromosome. When that plasmid gets ready to copy itself, the chromosomal genes are the first to be copied.

Unless the donor and recipient cells are able to maintain direct contact for a fairly long period of time, which almost never occurs, the recipient cell will not receive the plasmid. It will, however, receive numerous chromosomal genes from the donor. Those genes may later be incorporated into the chromosome of the recipient, causing gene replacement.

Not all species of bacteria participate in conjugation. Some rely on transduction as a means of receiving new genetic information. This is how Staphylococcus aureus has developed resistance to many antibiotics.

Transduction

Transduction
Transduction
There are two types of transduction: generalized and specialized. In both cases, a donor cell becomes infected with a bacteriophage, a virus that attacks bacteria. Upon the death of that donor cell, fragments of donor DNA are transferred as the escaping bacteriophage infects another bacterium.

In generalized transduction, a bacteriophage infects a bacterial cell. Shortly after infection, the bacterial chromosome becomes fragmented, and viral components are produced. Later the viral components are assembled to form a complete virus particle.

Occasionally during this assembly process, a particle becomes contaminated with fragments of the bacterial chromosome or plasmids. After assembly is completed, the bacterial cell ruptures, allowing the escape of all virus particles.

Eventually these virus particles will invade other bacterial cells. Any cells that are invaded by contaminated bacteriophage particles are said to be transduced, because they have received DNA from another bacterium. The DNA received in this manner is strictly random.

Specialized transduction involves what is known as a latent bacteriophage. After the initial invasion of a bacterium, the bacteriophage inserts itself into a specific region of that cell’s chromosome. At some later time, the bacteriophage removes itself from the chromosome and accidentally takes a few bacterial genes located near its original insertion point.

When the bacterial cell finally begins making new bacteriophage components, it behaves as if those particular genes are part of the bacteriophage and replicates them as such. Therefore, all the newly formed bacteriophage particles will contain those bacterial genes. Transduction then occurs when these bacteriophage particles invade other bacterial cells.

Transformation

Transformation
Transformation
The final method of genetic transfer is transformation. An extensively utilized organism for such investigation has been Streptococcus pneumoniae. The most famous studies involved converting nondisease-causing strains of Streptococcus pneumoniae intodisease-causing strains.

Transformation also occurs in a wide variety of other bacteria. The process of transformation requires that a population of actively reproducing bacteria come into contact with DNA fragments, often from closely related dead bacteria. These DNA fragments are referred to as either naked or cell-free DNA.

Genetic Modification

A small portion of that DNA can be absorbed and utilized by the growing bacteria. These recipients can then take advantage of any usable genes that the fragments might contain, incorporating them into their chromosome in place of their own copies of these genes by the process of recombination.

Conjugation, transduction, and transformation are all mechanisms of genetic change within a bacterial population. These mechanisms allow a specific characteristic to be spread throughout the population within a few hours.

A wide number of bacterial genes have been found to be transferred by these methods, including genes that control a bacterium’s ability to cause disease, to produce toxins, and to develop resistance to antibiotics and other drugs as well as genes that control a number of other characteristics.

The purpose of these mechanisms, as far as the bacteria are concerned, is to enable the bacteria to adapt to changing environmental conditions so that their survival is ensured. Scientists, however, have found ways to adapt some of these mechanisms for human benefit.

Scientists have used the mechanisms of genetic transfer along with new technology from DNA research to perform genetic engineering on bacteria. They can use genes and specially engineered plasmids, called plasmid vectors, to make recombinant DNA in the laboratory.

Recombinant plasmids can then be used to transform bacteria such as Escherichia coli (E. coli). The bacteria will treat these recombinant plasmids just like ordinary plasmids, replicating them and, for expression vectors, expressing any genes included in them.

In this manner, bacteria can be used to produce a wide variety of products for medicine, agriculture, and industry. Genetic engineering and the products that result from it would not be possible without the knowledge of genetic transfer gained from studies of bacterial conjugation, transduction, and transformation.
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4:08 PM
Biofertilizers
Biofertilizers
The use of biofertilizers, biological systems that supply plant nutrients such as nitrogen to agricultural crops, could reduce agriculture’s dependency on chemical fertilizers, which are often detrimental to the environment.

Plants require an adequate supply of the thirteen mineral nutrients necessary for normal growth and reproduction. These nutrients, which must be supplied by the soil, include both macronutrients (nutrients required in large quantities) and micronutrients (nutrients required in smaller quantities). As plants grow and develop, they remove these essential mineral nutrients from the soil.

Because normal crop production usually requires the removal of plants or plant parts, the nutrients are continuously removed from the soil. Therefore, the long-term agricultural utilization of any soil requires periodic fertilization to replace lost nutrients.

Nitrogen is the plant nutrient that is most often depleted in agricultural soils, and most crops respond to the addition of nitrogen fertilizer by increasing their growth and yield. Therefore, more nitrogen is applied to cropland than any other fertilizer component.


In the past, nitrogen fertilizers have been limited to either manures, which have low levels of nitrogen, or chemical fertilizers, which usually have high levels of nitrogen. However, the excess nitrogen in chemical fertilizers often runs off into nearby waterways, causing a variety of environmental problems.

Less Harmful Alternatives

Biofertilizers offer a potential alternative: They supply sufficient amounts of nitrogen for maximum yields yet have a positive impact on the environment. Biofertilizers generally consist of either naturally occurring or genetically modified microorganisms that improve the physical condition of soil, aid plant growth, or increase crop yield.

Biofertilizers provide an environmentally friendly way to increase plant health and yields with reduced input costs, new products and additional revenues for the agricultural biotechnology industry, and cheaper products for consumers.

Nitrogen Fixing

Nitrogen Fixing
Nitrogen Fixing
While biofertilizers could potentially be used to supply a number of different nutrients, most of the interest is focused on nitrogen. The relatively small amounts of nitrogen found in soil come from a variety of sources.

Some nitrogen is present in all organic matter in soil; as this organic matter is degraded by microorganisms, it can be used by plants. A second source of nitrogen is nitrogen fixation, the chemical or biological process of taking nitrogen from the atmosphere and converting it to a form that can be used by plants.

Bacteria such as members of Rhizobium can live symbiotically in the roots of certain plants, such as legumes. Rhizobia and plant root tissue form root nodules, which house the nitrogen-fixing bacteria; once inside the nodules, the bacteria use energy supplied by the plant to convert atmospheric nitrogen to ammonia, which nourishes the plant.

Natural nitrogen can also be supplied by free-living microorganisms, which can fix nitrogen without forming a symbiotic relationship with plants. The primary objective of biofertilizers is to enhance any one or all of these processes.

One of the major goals for the genetic engineering of biofertilizers is to transfer the ability to form nodules and establish effective symbiosis to non-legume plants. The formation of nodules in which the Rhizobia live requires plant cells to synthesize many new proteins, and many of the genes required for the expression of these proteins are not found in the root cells of plants outside the legume family (Fabaceae). If transfer of the appropriate genes could be accomplished, Rhizobia could be used as a biofertilizer for a variety of plants.

There is also much interest in using the free-living, soil-borne organisms that fix atmospheric nitrogen as biofertilizers. These organisms, including types bacteria and algae, live in the rhizosphere (the region of soil in immediate contact with plant roots) or thrive on the surface of the soil.

Because the exudates from these microorganisms contain nitrogen that can be used by plants, increasing their abundance in the soil could reduce the dependency on chemical fertilizers. Numerous research efforts have been designed to identify and enhance the abundance of nitrogen-fixing bacteria in the rhizosphere.

Soil microorganisms primarily depend on soluble root exudates and decomposed organic matter to supply the energy necessary for fixing nitrogen. Hence, there is also an interest in enhancing the biodegradation of organic matter in the soil.

This research has primarily centered on inoculating the soil with cellulose-degrading fungi and nitrogen fixing bacteria or applying organic matter, such as straw that has been treated with a combination of the fungi and bacteria to the soil.
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9:46 PM
Biopesticides
Biopesticides
Biopesticides are biological agents, such as viruses, bacteria, fungi, mites, and other organisms used to control insect and weed pests in an environmentally and ecologically friendly manner.

Biopesticides allow biologically based, rather than chemically based, control of pests. A pest is any unwanted animal, plant, or microorganism. When the environment provides no natural resistance to a pest and when no natural antagonists are present, pests can run rampant.

For example, spread of the fungus Endothia parasitica, which entered New York in 1904, caused the nearly complete destruction of the American chestnut tree because no natural control was present. Viruses, bacteria, fungi, protozoa, mites, insects, and flowers have all been used as biopesticides.

Advantages of Biopesticides

Many plants and animals are protected from pests by passive means. For example, plant rotation is a traditional method of insect and disease protection that is achieved by removing the host plant long enough to reduce a region’s pathogen and pest populations.


Biopesticides have several significant advantages over commercial pesticides. They appear to be ecologically safer than commercial pesticides because they do not accumulate in the food chain.

Some biopesticides provide persistent control, as more than a single mutation is required to adapt to them and because they can become an integral part of a pest’s life cycle. In addition, biopesticides have slight effects on ecological balances because they do not affect nontarget species. Finally, biopesticides are compatible with other control agents.

The major drawbacks to using biopesticides are the time required for them to kill their targets and the inefficiency with which they work; also, if the organism being used as a biopesticide is a nonnative species, it may cause unforeseen damage to the local ecosystem.

Viruses and Bacteria

Viruses and Bacteria
Viruses and Bacteria
Viruses have been developed against insect pests such as Lepidoptera (butterflies and moths), Hymenoptera (bees, wasps, and ants), and Dipterans (flies).Gypsymoths and tent caterpillars, for example, periodically suffer fromepidemic virus infestations, which could be exploited and encouraged.

Many commensal microorganisms (microorganisms that live on or in other organisms causing no direct benefit or harm) that occur on plant roots and leaves can passively protect plants against microbial pests by competitive exclusion (that is, simply crowding them out). Bacillus cereus has been used as an inoculumon soybean seeds to prevent infection by fungal pathogens in the genus Cercospora.

Some microorganisms used as biopesticides produce antibiotics, but the major mechanism in most cases seems to be competitive exclusion. For example, Agrobacterium radiobacter antagonizes Agrobacterium tumefaciens, which causes the disease crown gall.

Species of two bacterial genera—Bacillus and Streptomyces—when added as biopesticides to soil help control the damping-off disease of cucumbers, peas, and lettuce caused by Rhizoctonia solani. Bacillus subtilis added to plant tissue also controls stem rot and wilt rot caused by species of the fungus Fusarium.

Mycobacteria species produce cellulose degrading enzymes, and their addition to young seedlings helps control fungal infection by species of Pythium,Rhizoctonia, and Fusarium. Species of Bacillus and Pseudomonas produce enzymes that dissolve fungal cell walls.

Bacillus thuringiensis Toxins

The best examples of microbial insecticides are Bacillus thuringiensis (B.t.) toxins, which were first used in 1901. They have had widespread commercial production and use since the 1960’s and have been successfully tested on 140 insects, including mosquitoes.

Insecticidal endotoxins are produced by B.t. during sporulation, and exotoxins are contained in crystalline parasporal protein bodies. These protein crystals are insoluble in water but readily dissolve in an insect’s gut.

Once dissolved, the proteolytic enzymes paralyze the gut. Spores that have been consumed germinate and kill the insect. Bacillus popilliae is a related bacterium that produces an insecticidal spore that has been used to control Japanese beetles, a corn pest.

The gene for the B.t. toxin has also been inserted into the genomes of cotton and corn, producing genetically modified, or GM, plants that produce their own B.t. toxin. GM cotton and B.t. corn both express the gene in their roots, which provides them with protection from root worms.

Ecologists and environmentalists have expressed concern that constantly exposing pests to B.t. will cause insects to develop resistance to the toxin. In such a scenario, the effectiveness of traditionally applied B.t.would decrease.

Fungi and Protozoa

Saprophytic fungi can compete with pathogenic fungi. There are several examples of fungi used as biopesticides, such as Gliocladium virens, Trichoderma hamatum, Trichoderma harzianum, Trichoderma viride, and Talaromyces flavus. For example, Trichoderma species compete with pathogenic species of Verticillium and Fusarium.

Peniophora gigantea antagonizes the pine pathogen Heterobasidion annosum by three mechanisms: It prevents the pathogen from colonizing stumps and traveling down into the root zone, it prevents the pathogen from traveling between infected and uninfected trees along interconnected roots, and it prevents the pathogen from growing up to stump surfaces and sporulating.

Nematodes are pests that interfere with commercial button mushroom (Agaricus bisporus) production. Several types of nematode-trapping fungi can be used as biopesticides to trap, kill, and digest the nematode pests.

The fungi produce constricting and nonconstricting rings, sticky appendages, and spores, which attach to the nematodes. The most common nematode-trapping fungi are Arthrobotrys oligospora, Arthrobotrys conoides, Dactylaria candida, and Meria coniospora.

Protozoa have occasionally been used as biopesticide agents, but their use has suffered because of slow growth and the complex culture conditions associated with their commercial production.

Mites, Insects, and Flowers

Well-known “terminator” bugs include praying mantis and ladybugs as well as decollate snails, which eat the common brown garden snail. Fleas, grubs, beetles, and grasshoppers often have natural nematode species that prey on them, which can be used as biocontrol agents.

Predaceous mites are used as a biopesticide to protect cotton from other insect pests such as the bollwe evil. Parasitic wasps of the genus Encarsia, especially E. formosa, preyon whiteflies, as does Delphastus pusillus, a small, black ladybird beetle.

Dalmatian and Persian insect powders contain pyrethrins, which are a toxic insecticidal compounds produced in Chrysanthemum flowers. Synthetic versions of these naturally occurring compounds are found in products used to control head lice.
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7:44 AM
Biotechnology
Biotechnology
Biotechnology is the use of living organisms, or substances obtained from those organisms, to produce processes or products of value to humanity, such as foods, high-yield crops, and medicines.

Modern biotechnological advances have provided the ability to tap into a natural resource, theworld gene pool,with such great potential that its full magnitude is only beginning to be appreciated.

Theoretically, it should be possible to transfer one or more genes from any organism in the world into any other organism. Because genes ultimately control how any organism functions, gene transfer can have a dramatic impact on agricultural resources and human health in the future.

History of Biotechnology

Although the term “biotechnology” is relatively new, the practice of biotechnology is at least as old as civilization. Civilization did not evolve until humankind learned to produce food crops and domestic livestock through the controlled breeding of selected plants and animals. Eventually humans began to utilize microorganisms in the production of foods such as cheese and alcoholic beverages.


During the twentieth century, the pace of modification of various organisms accelerated. Through carefully controlled breeding programs, plant architecture and fruit characteristics of crops have been modified to facilitate mechanical harvesting. Plants have been developed to produce specific drugs or spices, andmicroorganisms have been selected to produce antibiotics and other medicinal or food products.

Developments in Biotechnology

Since the mid-twentieth century, the ability to utilize artificial media to propagate plants has led to the development of a technology called tissue culture. The earliest formof tissue culture involved using the culture of meristem tissue to produce numerous tiny shoots that can be grown into full-size plants, referred to as clones because each plant is genetically identical.

Developments in Biotechnology
Developments in Biotechnology
More than one thousand plant species have been propagated by tissue culture techniques. Plants have been propagated via the culture of other tissues, including the stems and roots. In some of these techniques, the plant tissue is treated with hormones to produce callus tissue, masses of undifferentiated cells.

The callus tissue can be separated into single cells to establish a cell suspension culture. Callus tissue and cell suspensions can be used to produce specific drugs and other chemicals. Entire plants can also be generated from the callus tissue or from single cells by addition of specific combinations of hormones.

Afar more complex method of cloning of plants and animals from the deoxyribonucleic acid (DNA) of a single cell is amore recent development. Proponents of this method of producing copies of organisms have suggested that cloning technology might be used to improve agricultural stock and to regenerate endangered species.

These ideas have had their detractors, however, as critics have noted the potential dangers of narrowing a species’ gene pool. The July, 1996, birth in Scotland of Dolly, a sheep cloned and raised to adulthood, demonstrated that the cloning of animals had left the realm of science fiction and become a matter of scientific fact.

Recombinant DNA Technology

In practice, recombinant DNA methodology is complex, but in concept, it is fairly easy to comprehend. The genes in all living cells are composed of the same chemical, DNA. The DNA of all cells, whether from bacteria, plants, or animals including humans, is very similar. When DNA from a foreign species is transferred into a different cell, it functions exactly as the native DNA functions; that is, it "codes" for protein.

The easiestway to manipulate genes is using bacterial cells (most often Escherichia coli) and a vector, an agent that can be used to pass the gene fromone cell to another. Plasmids, small extra circular DNA molecules found in many bacterial cells, are commonly used for this purpose. Plasmids are replicated along with the bacterial cell’s own DNA every time the cell reproduces. Plasmids can be easily isolated from bacterial cells.

Recombinant DNA Technology
Recombinant DNA Technology
When a specific gene has been isolated, it can be fused, using restriction endonucleases, with a plasmid to produce a recombinant plasmid. These recombinant plasmids can then be put into bacterial cells by a process called transformation. Special plasmids called expression vectors allow expression of inserted genes once they are inside a bacterial cell.

Although expressing foreign genes in bacterial cells is relatively simple, inserting theminto plants and getting them expressed is more complicated. The Ti plasmid is a widely used vector that works well in dicots but has never worked for monocots. Consequently, the first successful transgenic plants were dicots, while success with the most important food crops, monocots such as rice and corn, took more time and effort.

Many alternative methods for inserting genes into plant cells have been developed that work on both monocots and dicots. Microinjection can be used to insert a gene into individual cells. A less laborious method is called biolistic, for biological ballistic, where millions of copies of the gene are attached to tiny projectiles that are then fired into groups of plant cells. Using these and other methods, genetic modification of plants is becoming more routine.

Future of Biotechnology in Agriculture

This new technology could have a tremendous impact on agriculture. As the human population grows, biotechnology will most likely play an important role in producing an increase in food production. Such an increase will require developments such as crop plants that will produce higher yields under normal conditions and crops that will produce higher yieldswhen grown inmarginal environments.

Biotechnology provides a means of developing higher-yielding crops in much less time than it takes to develop them though traditional plant-breeding programs. Genes for the desired characteristics can be inserted directly into the plant without having to go through repeated controlled selection and breeding cycles to establish the trait.

There are also economic advantages in diversifying agriculture production in a given area. A producer might wish to grow a particular high-value cash crop in an area where soil or climate conditions would prevent such a crop from thriving. Biotechnology can help solve these types of problems. For example, high value crops can be developed to grow in areas that heretofore would not have supported such crops.

Plants also can be developed to produce new products such as antibiotics, drugs, hormones, and other pharmaceuticals. Crop plants bioengineered to produce novel products mean that pharmaceuticals and other valuable products could be grown in farm environments rather than in laboratories.

While there will be a growing pressure for agriculture to produce more food in the future, there will also be pressure for crop production to be more friendly to the environment. Biotechnology has the potential to play a major role in the development of a long-term, sustainable, environmentally friendly agricultural system. For example, the development of crop varieties with improved resistance to pests will reduce the reliance on pesticides.

Methods of crop production and harvestwith less environmental impact will also have to be developed. Because agriculture will continue to have an impact on the environment, the need to remediate polluting agents will continue to exist. Hence biotechnology will play an important role in the development of bioremediation systems for agriculture as well as other industrial pollutants.

Ownership Issues

There will be many difficult ethical and economic issues surrounding the use of this new biotechnology. One of the major questions concerns ownership. Patent laws in the United States read that ownership over an organism can be granted if the organism has been intentionally genetically modified through the use of recombinant DNA techniques.

In addition, processes that utilize genetically modified organisms can be patented. Therefore one biotechnology firm may own the patent to an engineered organism, but another firm may own the rights to the process used to produce it.
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