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