ENVIRONMENTAL AND INDUSTRIAL MICROBIOLOGY

Environmental microbiology pertains to the study of microbiology of soil, microbiology of aquatic systems, microbiology of domestic water and wastewater and also microbiology of foods.

This study at different source levels provides an insight into life under extreme conditions, i.e. harsh environmental conditions. For example, surface water of the ocean contains many microorganisms, and it has long been thought that relatively a few bacteria exist on the deep ocean floor because of low temperature of the water, scarcity of nutrients and absence of light to support the growth of phototrophic organisms, and the enormous hydrostatic pressure due to the great depth of overlying water column.

This is true for most regions of the ocean floor, but a startling exception was found somewhere in the 1970s during the exploration of deep sea hydrothermal vents (hot submarine springs) located along submarine tectonic rifts and ridges of the ocean floor at a depth of 2500–2600 metres. In the areas surrounding these vents, living organisms were discovered in abundance right from bacteria to invertebrates. Life exist here because these hot springs

can produce geothermally hydrogen sulphide and other reduced inorganic compounds and release into the surrounding water, which can be a source of carbon and energy.

1.7.1 Microbiology of Soil

Seemingly the earth looks dead, but a paragraph in the article “A Microbiologist Digs in the Soil” by Charles Thom reveals some interesting facts:

Bacillus tetanus, amoebic dysentery, thermophilic spoilage, Actinomycosis and Botulism today are much spoken of. This is because the soil harbors millions of organisms and can be taken as “Lilliputian zoo” which infest in wound, clothing and food. Directly or indirectly the wastes of humans and other animals, their bodies and tissues of plants are dumped or buried in the soil. They all disappear somehow; transform into the substances that make up the soil.

It is the microbes that bring the transformations—the conversion of organic matter into simple inorganic substances that provide the nutrient material for the plant world.

The transformations are brought by the following cycles: carbon cycle, nitrogen cycle, sulphur cycle, etc. The microbial flora of the soil consists of bacteria, fungi, algae, protozoa, viruses, rhizospheres etc.

The biodegradation of herbicides, pesticides, etc. is also brought about by the microorganisms and the process can be called soil/land reclamation.

1.7.2 Aquatic Microbiology

Aquatic microbiology is the study of microorganisms and their activities in the fresh, estuarine, and marine waters, including the springs, lakes, rivers, bays and the seas. It is the study of microorganisms like viruses, bacteria, algae, protozoa and fungi which inhabit these natural waters.

Some microorganisms are indigenous to the natural bodies of water, others are transient, entering water from air, soil, or from industrial or domestic wastes. Wastewaters usually contain microorganisms which influence the activities of microorganisms already present in the receiving waters.

Aquatic microorganisms and their activities are of great importance. They affect the health of humans and other animal life. Occupy a key position in the food chain by providing the rich nourishment for the next higher level of aquatic life. They are instrumental in the chain of biochemical reactions which accomplish recycling of the elements, for example, in the process of mineralization. The aquatic environment is influenced by the following factors. They are temperature, hydrostatic pressure, light, salinity, turbidity, pH, inorganic and organic constituents.

The temperature of surface waters is 0°C in the polar regions and 30–40°C in the equatorial regions. More than 90% of the marine environment

is below 5°C, a condition favourable for psychrophillic microorganisms. Some microorganisms occur in the natural hot springs where temperature is as high as 75–80°C and these microorganisms are called Thermus aquaticus.

Recently microbiologists have reported extreme thermophilic micro- organisms associated with the geothermal vents in the Pacific Ocean floor and they can grow at a temperature as high as 250°C and at a pressure of 265 atmospheres. The hydrostatic pressure affects the chemical equilibrium, which results in lowering the pH of sea water, resulting in a change in the solubility of nutrients such as bicarbonates, HCO3–, etc.

It also increases the boiling point of water, thereby, maintaining water in its liquid state at high temperatures and pressures.

Salinity ranges from zero of fresh water to saturation in salt lakes. The concentration of dissolved salts ranges from 33–37 grams per kilogram of water. The pH value of sea water is generally between 7.5 and 8.5, and the microorganisms can grow at a pH of 6.5 to 8.5.

1.7.3 Domestic Water and Wastewater Microbiology

The sources of domestic water are rivers, streams, lakes, etc. Rivers and streams get polluted particularly with the domestic and the industrial wastes and become the carrier of pathogenic microorganisms that cause diseases like infection of the intestinal tract, typhoid, dysentery (bacillary and amoebic) and enteric fever. The causative organisms of these diseases are present in the faeces or urine of an infected person, and when discharged may gain entrance into a body of water that ultimately serves as a source of drinking water. Wastewater treatment procedures, both natural and artificial, are largely dependent upon microbial activity to eliminate or greatly reduce the develop- ment of hazardous or objectionable situations. Activated sludge processes, trickling filters, oxidation ponds, etc. are some of the processes used to treat the wastewaters from the industry.

Note: Elementary concepts on the above are discussed in Appendix C.

1.7.4 Microbiology of Foods

Microorganisms are also associated in several ways with all the food we eat. They influence the quality, availability, and the quantity of our food. One of the activities of microorganisms upon food is food spoilage. To avoid food spoilage, some preservation techniques are used. They are aseptic handling, high temperature, canning, pasteurization, sterilization, aseptic processing, and freezing. Lyophilization also known as freeze drying is done to remove moisture content of foodstuffs so that they can be safely stored for a longer period of time.