| In this introductory article we will briefly define | | | | acid (see Lactobacillus), as well as fermenting |
| bacteria, outline the history of bacteriology, examine | | | | complex undigestible carbohydrates. The presence |
| some of their interactions with other organisms | | | | of this gut flora also inhibits the growth of potentially |
| before discussing the significance of bacteria in | | | | pathogenic bacteria (usually through competitive |
| technology and industry | | | | exclusion) and these beneficial bacteria are |
| What are bacteria ? | | | | consequently sold as probiotic dietary supplements. |
| Bacteria are a large group of | | | | Pathogens |
| unicellular, prokaryote, microorganisms. Typically a | | | | If bacteria form a parasitic association with other |
| few micrometres in length, bacteria have a wide | | | | organisms, they are classed as pathogens. |
| range of shapes, ranging from spheres to rods and | | | | Pathogenic bacteria are a major cause of human |
| spirals. Bacteria are ubiquitous in every habitat on | | | | death and disease and cause infections such |
| Earth, growing in soil, acidic hot springs, radioactive | | | | as tetanus, typhoid |
| waste (see below), water, and deep in the Earth's | | | | fever, diphtheria, syphilis, cholera, foodborne |
| crust, as well as in organic matter and the live bodies | | | | illness, leprosy and tuberculosis. A pathogenic cause |
| of plants and animals. There are typically 40 million | | | | for a known medical disease may only be discovered |
| bacterial cells in a gram of soil and a million bacterial | | | | many years after, as was the case withHelicobacter |
| cells in a millilitre of fresh water; in all, there are | | | | pylori and peptic ulcer disease. Bacterial diseases are |
| approximately five nonillion (5×1030) bacteria on | | | | also important in agriculture, with bacteria |
| Earth, forming much of the world's biomass | | | | causing leaf spot, fire blight and wilts in plants, as |
| according to an article by Whitman WB, Coleman DC, | | | | well as Johne's |
| Wiebe WJ (June 1998). "Prokaryotes: the unseen | | | | disease, mastitis, salmonella and anthrax in farm |
| majority" . | | | | animals. |
| Bacteria are vital in recycling nutrients, with many | | | | Each species of pathogen has a characteristic |
| steps in nutrient cycles depending on these | | | | spectrum of interactions with its human hosts. Some |
| organisms, such as the fixation of nitrogen from | | | | organisms, such as Staphylococcus orStreptococcus, |
| the atmosphere and putrefaction. However, most | | | | can cause skin infections, pneumonia, meningitis and |
| bacteria have not been characterized, and only about | | | | even overwhelming sepsis, a systemic inflammatory |
| half of the phyla of bacteria have species that can | | | | responseproducing shock, massive vasodilation and |
| be grown in the laboratory. The study of bacteria | | | | death. Yet these organisms are also part of the |
| is known as bacteriology, a branch of microbiology. | | | | normal human flora and usually exist on the skin or in |
| There are approximately ten times as many bacterial | | | | the nose without causing any disease at all. Other |
| cells in the human flora of bacteria as there are | | | | organisms invariably cause disease in humans, such as |
| human cells in the body, with large numbers of | | | | the Rickettsia, which are obligate intracellular |
| bacteria on the skin and as gut flora. The vast | | | | parasites able to grow and reproduce only within the |
| majority of the bacteria in the body are rendered | | | | cells of other organisms. One species of Rickettsia |
| harmless by the protective effects of the immune | | | | causestyphus, while another causes Rocky Mountain |
| system, and a few are beneficial. However, a few | | | | spotted fever. Chlamydia, another phylum of obligate |
| species of bacteria are pathogenic and | | | | intracellular parasites, contains species that can cause |
| cause infectious diseases, including cholera, | | | | pneumonia, or urinary tract infection and may be |
| syphilis, anthrax, leprosy and bubonic plague. The | | | | involved in coronary heart disease. |
| most common fatal bacterial diseases are respiratory | | | | Significance of bacteria in technology and industry |
| infections, with tuberculosis alone killing about 2 | | | | Bacteria, often lactic acid bacteria such |
| million people a year, mostly in sub-Saharan Africa. | | | | as Lactobacillus and Lactococcus, in combination |
| .In developed countries, antibiotics are used to | | | | with yeasts and molds, have been used for |
| treat bacterial infections and in agriculture, | | | | thousands of years in the preparation |
| so antibiotic resistance is becoming common. In | | | | of fermented foods such as cheese, pickles, soy |
| industry, bacteria are important in sewage | | | | sauce,sauerkraut, vinegar, wine and yoghurt. |
| treatment, the production of cheese and | | | | The ability of bacteria to degrade a variety of |
| yoghurt through fermentation, as well as | | | | organic compounds is remarkable and has been used |
| in biotechnology, and the manufacture of antibiotics | | | | in waste processing and bioremediation. Bacteria |
| and other chemicals. | | | | capable of digesting |
| Once regarded as plants constituting the class | | | | the hydrocarbons in petroleum are often used to |
| Schizomycetes, bacteria are now classified | | | | clean up oil spills. For example in a recent article by |
| as prokaryotes. Unlike cells of animals and | | | | Marcela Valente entitled " Bacteria eat up oil in |
| othereukaryotes, bacterial cells do not contain | | | | Antarctica" we know that Argentine scientists are |
| a nucleus and rarely | | | | developing a biological process for combating oil spills |
| harbour membrane-bound organelles. Although the | | | | in the extremely cold temperatures of the immense |
| term bacteria traditionally included all prokaryotes, | | | | ice-covered continent. Here is an extract from that |
| the scientific classification changed after the | | | | article: |
| discovery in the 1990s that prokaryotes consist of | | | | "BUENOS AIRES - For the past 25 years it has been |
| two very different groups of organisms | | | | known that certain bacteria are useful for cleaning up |
| that evolved independently from an ancient | | | | oil spills in warmer climates, where the microorganisms |
| common ancestor. These evolutionary domains are | | | | easily reproduce and decompose contaminants. This |
| called Bacteria and Archaea. | | | | technique might now be used in Antarctica, thanks to |
| History of bacteriology | | | | the discoveries of two Argentine scientists. Biologist |
| Bacteria were first observed by Antonie van | | | | Walter MacCormack, of the Argentine Antarctic |
| Leeuwenhoek in 1676, using a | | | | Institute, and biochemist Lucas Ruberto, of the |
| single-lens microscope of his own design. He called | | | | University of Buenos Aires, set out to find an |
| them "animalcules" and published his observations in a | | | | efficient "biological remediation process" for |
| series of letters to the Royal Society. The | | | | extremely cold conditions, like those in Antarctica, |
| name bacterium was introduced much later, | | | | where the average temperature is below |
| by Christian Gottfried Ehrenberg in 1838. | | | | freezing. Such processes, using microorganisms to |
| Louis Pasteur demonstrated in 1859 that | | | | clean up soil contaminated by fossil fuels or heavy |
| the fermentation process is caused by the growth | | | | metals, have an established history. But "the bacteria |
| of microorganisms, and that this growth is not due | | | | that break down fossil fuels tend to reproduce at |
| to spontaneous generation. (Yeasts and molds, | | | | temperatures between 20 and 30 degrees Celsius," |
| commonly associated with fermentation, are not | | | | MacCormack told Tierramérica. "At four degrees, |
| bacteria, but rather fungi.) For more information | | | | they do not grow, and the (decontamination) |
| please see our series on eminent anatomists and | | | | processes were not successful or were too slow to |
| physiologists. | | | | be considered efficient," he added. And there was |
| Along with his contemporary, Robert Koch, Pasteur | | | | another problem. The Madrid Protocol, which |
| was an early advocate of the germ theory of | | | | establishes environmental protection standards for |
| disease. Robert Koch was a pioneer in medical | | | | Antarctica, prohibits the introduction of viruses, |
| microbiology and worked | | | | bacteria or any microorganism from other regions, |
| on cholera, anthrax and tuberculosis. In his | | | | and also bans taking samples from the frozen |
| research into tuberculosis, Koch finally proved the | | | | continent, except for previously authorized scientific |
| germ theory, for which he was awarded a Nobel | | | | purposes." |
| Prize in 1905. In Koch's postulates, he set out | | | | In another case fertilizer was added to some of the |
| criteria to test if an organism is the cause of | | | | beaches in Prince William Sound in an attempt to |
| a disease; these postulates are still used today. | | | | promote the growth of these naturally occurring |
| Though it was known in the nineteenth century that | | | | bacteria after the infamous 1989 Exxon Valdez oil |
| bacteria are the cause of many diseases, no | | | | spill. These efforts were effective on beaches that |
| effective antibacterial treatments were available. In | | | | were not too thickly covered in oil. |
| 1910, Paul Ehrlich developed the first antibiotic, by | | | | Bacteria may also be of use in dealing with |
| changing dyes that selectively stained Treponema | | | | radioactive waste. According to an article by Tom |
| pallidum—thespirochaete that | | | | Paulson in the Seattle Post Scientists studying the soil |
| causes syphilis—into compounds that selectively | | | | beneath a leaking Hanford nuclear waste storage |
| killed the pathogen. Ehrlich had been awarded a 1908 | | | | tank have discovered more than 100 species of |
| Nobel Prize for his work on immunology, and | | | | bacteria living in a toxic, radioactive environment that |
| pioneered the use of stains to detect and identify | | | | most would have thought inhospitable to all forms of |
| bacteria, with his work being the basis of the Gram | | | | life."Even in some of the most contaminated zones, |
| stain and the Ziehl-Neelsen stain. | | | | we found a few living organisms," said Fred |
| A major step forward in the study of bacteria was | | | | Brockman, a microbial ecologist at the Pacific |
| the recognition in 1977 by Carl | | | | Northwest National Laboratory in Richland. The waste |
| Woese that archaea have a separate line of | | | | in the Hanford tanks is made up of highly radioactive |
| evolutionary descent from bacteria. This | | | | cesium, strontium and various other toxic chemicals |
| new phylogenetic taxonomy was based on | | | | left over from the World War II bomb works. About |
| the sequencing of 16S ribosomal RNA, and divided | | | | 53 millions gallons was stored in 177 underground |
| prokaryotes into two evolutionary domains, as part | | | | tanks, some of which have leaked an estimated 1 |
| of the three-domain system. As stated above for | | | | million gallons into the surrounding soil of the Columbia |
| more information please consult our article "Eminent | | | | Basin. "One of the most interesting findings was a |
| Anatomists and Physiologists" in this series. | | | | strain of Deinococcus," Fredrickson said. It's a type of |
| Interactions with other organisms | | | | bacteria that's been found in Antarctica and on |
| Despite their apparent simplicity, bacteria can form | | | | irradiated meat, he said, but never at Hanford before. |
| complex associations with other organisms. | | | | Brockman said they didn't discover any new species |
| These symbiotic associations can be divided | | | | of bug -- based on the standard method for |
| into parasitism, mutualism andcommensalism. Due | | | | identifying species -- but genetic analysis of the |
| to their small size, commensal bacteria are ubiquitous | | | | Hanford versions of these bacteria indicate they may |
| and grow on animals and plants exactly as they will | | | | have at least found some unique new strains. |
| grow on any other surface. However, their growth | | | | Bacteria are also used for the bioremediation of |
| can be increased by warmth and sweat, and large | | | | industrial toxic wastes. In the chemical industry, |
| populations of these organisms in humans are the | | | | bacteria are most important in the production |
| cause of body odor. | | | | of enantiomerically pure chemicals for use |
| Predators | | | | as pharmaceuticals or agrichemicals. |
| Some species of bacteria kill and then consume other | | | | Bacteria can also be used in the place |
| microorganisms, these species called predatory | | | | of pesticides in the biological pest control. This |
| bacteria.These include organisms such | | | | commonly involves Bacillus thuringiensis (also called |
| as Myxococcus xanthus, which forms swarms of | | | | BT), a Gram-positive, soil dwelling bacterium. |
| cells that kill and digest any bacteria they encounter. | | | | Subspecies of this bacteria are used as |
| Other bacterial predators either attach to their prey | | | | a Lepidopteran-specific insecticides under trade |
| in order to digest them and absorb nutrients, such | | | | names such as Dipel and Thuricide. Because of their |
| asVampirococcus, or invade another cell and multiply | | | | specificity, these pesticides are regarded |
| inside the cytosol, such as DaptobacterThese | | | | as environmentally friendly, with little or no effect on |
| predatory bacteria are thought to have evolved | | | | humans, wildlife, pollinators and most |
| from saprophages that consumed dead | | | | other beneficial insects according to an article by |
| microorganisms, through adaptations that allowed | | | | Chattopadhyay A, Bhatnagar N, Bhatnagar R (2004). |
| them to entrap and kill other organisms. | | | | "Bacterial insecticidal toxins". Crit Rev Microbiol. |
| Mutualists | | | | Because of their ability to quickly grow and the |
| Certain bacteria form close spatial associations that | | | | relative ease with which they can be manipulated, |
| are essential for their survival. One such mutualistic | | | | bacteria are the workhorses for the fields |
| association, called interspecies hydrogen transfer, | | | | of molecular biology, genetics and biochemistry. By |
| occurs between clusters of anaerobic bacteria that | | | | making mutations in bacterial DNA and examining the |
| consume organic acids such as butyric | | | | resulting phenotypes, scientists can determine the |
| acid or propionic acid and produce hydrogen, | | | | function of genes, enzymes and metabolic |
| and methanogenic Archaea that consume | | | | pathways in bacteria, then apply this knowledge to |
| hydrogen. The bacteria in this association are unable | | | | more complex organisms. This aim of understanding |
| to consume the organic acids as this reaction | | | | the biochemistry of a cell reaches its most complex |
| produces hydrogen that accumulates in their | | | | expression in the synthesis of huge amounts |
| surroundings. Only the intimate association with the | | | | of enzyme kinetic and gene expression data |
| hydrogen-consuming Archaea keeps the hydrogen | | | | into mathematical models of entire organisms. This |
| concentration low enough to allow the bacteria to | | | | is achievable in some well-studied bacteria, with |
| grow. | | | | models of Escherichia coli metabolism now being |
| In soil, microorganisms which reside in | | | | produced and tested. This understanding of bacterial |
| the rhizosphere (a zone that includes | | | | metabolism and genetics allows the use |
| the root surface and the soil that adheres to the | | | | of biotechnology to bioengineer bacteria for the |
| root after gentle shaking) carry out nitrogen fixation, | | | | production of therapeutic proteins, such |
| converting nitrogen gas to nitrogenous | | | | as insulin, growth factors, or antibodies. |
| compounds. This serves to provide an easily | | | | In conclusion our knowledge and understanding of |
| absorbable form of nitrogen for many plants, which | | | | bacteria is only just beginning especially when we |
| cannot fix nitrogen themselves. Many other bacteria | | | | consider the exciting developments in studies |
| are found as symbionts in humans and other | | | | involving extremophile bacteria that tolerate extreme |
| organisms. For example, the presence of over 1,000 | | | | cold, pressure, acidity, alkaline environments or |
| bacterial species in the normal human gut flora of | | | | combinations of these in addition to radiation. The |
| the intestines can contribute to gut immunity, | | | | uses of bacteria even extend beyond our world into |
| synthesise vitamins such as folic acid, vitamin | | | | the potential of astrobiology. |
| K and biotin, convert milk protein to lactic | | | | |