MICROBIOLOGY Study Guide - 2012

CHAPTER 10. MICROBIAL ECOLOGY

Microbial Ecology (from the Greek oicos meaning house or dwelling) examines the development and functioning of individual microbial species and their communities (microbiocenoses) in natural environments. Microorganisms are present in all biospheric ecosystems, including soil, Water, and air. They inhabit plants as well as the bodies of humans, animals, birds, and insects.

10.1. SOIL MICROFLORA

Soil is densely populated with microorganisms, harboring every form of microbial life found on Earth: Bacteria, Viruses, actinomycetes, Yeasts, Fungi, and Protozoa. Soil microorganisms play a vital role in pedogenesis (soil formation), self-purification, and the global biogeochemical cycles of nitrogen, carbon, and other elements. As a habitat, soil is highly heterogeneous. The species composition of soil microflora depends on its type and condition, chemical composition, The ratio of specific components, Temperature, moisture, and other factors. Microbial Abundance varies across different soil layers. The total count of microorganisms in 1 g of soil ranges from 10⁹ to 10¹⁰ CFU. In the uppermost layer (0,5 cm), the microbial population is very sparse due to the detrimental effects of UV radiation, desiccation, and other adverse factors. At depths ranging from 1—5 cm to 30—40 cm, microbial numbers peak, averaging 10—50 million per gram. Below 30—40 cm, microbial density declines, remaining sparse in deeper strata.

The soil hosts nitrogen-fixing (Azotobacter; Azomonas), nitrifying (Nitrobacter, Nitrosomonas), denitrifying, and butyric acid bacteria. Among putrefactive bacteria, the most frequently detected are aerobic bacilli such as Bacillus subtilis, В. mycoides, В. megatherium, anaerobic clostridia including Clostridium sporogenes, С. perfringens, С. putrificum, and non-spore-forming rods of the genera Pseu-domonas and Proteus.

Actinomycetes and numerous fungal representatives are permanent residents of the soil, although the abundance of fungi is relatively low (accounting for about 1% of the total microflora).

Soil also contains microorganisms introduced from water, air, animals, and plants. Pathogenic and opportunistic microorganisms enter the soil via wastewater. The survival time of pathogens in the soil depends on the microbial species, environmental conditions, and the intensity of self-purification processes.

Soil can serve as a transmission vehicle for the causative agents of numerous infectious diseases, such as anthrax, gas gangrene, and tetanus. When soil is contaminated with feces from individuals suffering from intestinal infections, plant-derived products can become contaminated with pathogens responsible for dysentery, cholera, typhoid fever, salmonellosis, and enteroviruses. A direct correlation has been established between the incidence of intestinal infections in humans and animals and the poor sanitary condition of the soil.

Sanitary and MICROBIOLOGICAL ANALYSIS OF soil involves determining the total microbial count and the presence of sanitary-indicator microorganisms (SIM), such as coliform bacteria, Clostridium perfringens, and Enterococcus faecalis. The microbial count reflects the degree of organic pollution in the soil, while the presence of SIM indicates fecal contamination.