A BRIEF SURVEY OF MICROBES AS FRIENDS AND FOES

INTRODUCTION

Microorganisms occur in large numbers of most natural environments and bring about many changes. Some are desirable and others are undesirable. Microorganisms affect the well being of people in many ways. Many are beneficial to man and can be called ‘friends’ while some are harmful and can be regarded as ‘foes’ to man. The beneficial impact of microorganisms ranges from the production of goods and pharmaceutical products, to enhancement of soil fertility, environmental cleanup while their harmful effect can be seen in their ability to cause disease in man, animals and plants as well as their usage in biological warfare. However, there are more species of microorganisms that perform friendly and beneficial functions than those that harm other living organisms. This unit gives us a brief survey of microorganisms as friends and foes.

Microorganisms as Friends

Microorganisms have found application in various aspects of life. They are useful in food industries to produce many food substances, in medicine to produce vaccines and antibiotics, in environmental protection, and in agriculture, to optimise yield.

Microorganisms and Food Production

  1. Many microorganisms are used to produce many of the foods and beverages we consume. Microbially-produced food products have properties that are very different from those of the starting materials. Most of these food products are produced by fermentation.
  2. Fermentation is the chemical transformation of organic compounds carried out by microorganisms and their enzymes. In industrial fermentation, raw materials (substrate) are converted by microorganisms in a controlled favourable environment (created in a fermentor) to form a desired end product substance.
  3. The accumulation of fermentation products such as ethanol and lactic acid produces characteristic flavours and other desirable properties in food substances.
  4. Pickles and some sausages are also produced by fermentation processes.
  5. Microorganisms are used to produce fermented dairy products such as cheese, yoghurt and acidophilus milk.
  6. They are also used to produce alcoholic beverages such as beer by conversion of sugar to alcohol and carbon dioxide.
  7. Wine fermented from fruits using yeast strains Saccharomyces cerevisiae and bread is also produced by using yeasts.
  8. Microorganisms can also be used as direct source of food known as single cell protein. Various species of yeasts, algae are grown as single cell protein and use as animal feeds thus helping to meet the world food needs.

 Production of Pharmaceuticals

Microorganisms are used to produce different pharmaceuticals such as antibiotics, steroids vitamins, hormones, etc. Antibiotics are microbially produced substances or substances synthetically derived from natural sources that inhibit or kill microorganisms, Steroids regulate various aspects of human metabolisms and are produced by organisms such Rhizopus nigricans.

Vaccines are produced using microorganisms with the antigenic properties to elicit a primary immune response; they are used to prevent many once deadly diseases such as polio, small pox, tuberculosis, measles, diphtheria and whooping cough.

Vitamins

Vitamins are essential animal nutritional factors; some vitamins are produced by microbial fermentation, e.g. Vitamin B12 by Streptomyces, B12 by Pseudomonas denitrificans and Propionibacterium shermanni. Riboflavin produced by various species of Clostridium and Ashbya gossypii. Human insulin and human growth hormone are produced by genetically engineered bacteria.

Production of Organic Acids

Various organic acids are produced by microorganisms examples are:

  1. Gluconic acid: used as a pharmaceutical to supply calcium to the body by several fungi including Penicillium and Aspergillus species. Citric acid produced by Aspergillus niger and used as a food additive especially in the production of soft drinks.
  2. Gibberellic acid: a plant hormone is formed by the fungus. Gibberella fujikuroi. It is used as growth promoting substances to stimulate plant growth flowering and seed germination.
  3. Lactic acid by different lactic acid bacteria for example, Lactobacillus delbrueckii, lactic and is used in foods as preservatives, in leather production for deliming hides and in the textile industry for fabric treatment, plastics making in baking powders

Hygiene

  1. Hygiene is the avoidance of infection and food spoilage by eliminating microorganisms from the surrounding.
  2. Our knowledge of how disease causing microorganisms spread has permitted us to reduce the incidence of many diseases. Also improved sanitation practices have helped to reduce the incidence of diseases.
  3.  Microorganisms from the surroundings can be totally removed by methods such as sterilization or reduced to acceptable levels using methods such as disinfection and antisepsis. In food preparation, microbes are reduced to acceptable levels using methods such as pasteurization, addition of vinegar. While complete sterility is achieved by autoclaving or irradiation.

Energy Production

Microorganisms play major roles in energy production. Microbes are used in fermentation to produce ethanol and in biogas reactions to produce methane using various forms of agricultural and urban wastes. Microbial production of synthetic fuels acts as an alternative fuel resources to petroleum.
The microbial production of ethanol from sugarcane or cornstarch has become an important source of a valuable fuel, particularly in areas of the world that have abundant supplies of plant residues such as Brazil and is becoming popular in the United States.

The bacteria Zymomonas mobilis and Thermoanaerobacter ethanolicus and different yeast strains are used for product of ethanol. Methane (natural gas) is produced by methanogenic bacteria is another important natural renewable energy sources.
Methane can be used for the generation of mechanical, electrical and heat energy.

 Useful in the Study of Science

Microbes are essential tools in biotechnology, biochemistry, genetics molecular biology and genomics. Examples are the yeasts (Saccharomyces cerevisiae) and fission yeast (Shizosaccharomyces pombe) which are model organisms in science. They can easily be grown rapidly in large quantities and are easily manipulated. Biotechnology uses genetic engineering which is the artificial manipulation of genes and gene products. Genes from any source can be manipulated and modified using microorganisms and their enzymes as molecular tools, e.g. human insulin, a hormone which is very low in people with diabetes is produced by genetically engineered bacteria into which human genes have been inserted.

 Recovery of Metals from their Ores

Microorganisms are used to recover metals from their ores by the process of bioleaching. Bioleaching uses microorganisms to alter the physical or chemical properties of a metallic ore so that the metal can be extracted. The bacteria Thiobacillus feroxidans recover copper and uranium from their ores.

Microorganisms and Agriculture

  1. Agriculture depends in many ways on the activities of microorganisms. Microorganisms help in nitrogen fixation used by plants for growth.
  2. In terrestrial habitats, the microbial fixation of atmospheric nitrogen is carried out by free living bacteria such as Rhizobium and Bradyrhizobium living in symbiotic association with plants. · Legumes live in close association with bacteria that form structures called nodules on their roots.
  3. These bacteria in the root nodules of the legumes, convert atmospheric N fixed into Nitrogen (NH) that plants use for growth and eradicates the need for chemical fertilizers.
  4. Microorganisms in the rumen of ruminant animals such as cattle and sheep also help in the digestion of cellulose present in grasses on which they feed on.

Microorganisms and the Environment

  1. Microorganisms can be used to clean up pollution created by human activities in a process called bioremediation.
  2. Pollutants such as pesticides, spilled oil solvents which could pose human health hazard are degraded to nontoxic substances by microorganisms.
  3. Microorganisms are used to degrade wastes and pollutants so as to maintain and restore environmental quality.

Sewage Treatment

Microorganisms are also used in sewage treatment. Specially cultured microbes are used in the biological treatment of sewage and industrial waste effluent in a process known as bioaugmentation. These microbes help to get rid of waste materials which could have accumulated in the environment.

GENERAL MICROBIOLOGY

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