In this article we will discuss about the important microorganisms that occur in varying water habitats.
The type of microbial populations differ in different type of water habitats such as unpolluted, polluted, and marine waters.
Table 31.1 represents the important microorganisms occurring in varying water habitats:
Microorganisms in Unpolluted Water:
In unpolluted water of mountain lake or stream there are usually low organic nutrients. The number of bacteria is very much limited, a few thousand per ml. Actinomycetes are typical. Autotrophic bacteria are common along-with free-living protozoans as Euglena, Paramecium and various amoebae. Other, organisms shown in Table 31.1 are also present.
Microorganisms in Polluted Water:
In polluted waters, there are large amounts of organic matter from sewage, faces and industrial complex. The microbes are usually heterotrophic. The digestion of organic matter by these organisms is incomplete, due to which there accumulate acids, bases, alcohols, and various gases.
The major type of bacteria are coliform bacteria, the gram-negative non-spore-forming bacilli usually found in the intestine. This group includes E. coli and species of Enterobacter. They ferment lactose to acid and gas. Non-conform bacteria such as Streptococcus, Proteus, and Pseudomonas are also present.
Under certain conditions, the polluting organisms multiply rapidly and consume most of the available oxygen. For convenience, nutrients enter the river from sources like sewage treatment plants or urban/suburban runoff. Thus river suddenly develops a high nutrient content. Under these conditions algae may bloom rapidly.
This leads to depletion of oxygen in water. There is very little oxygen available to the protozoa, small animals, fish and plants. Due to this non-availability of oxygen, a layer of dead organisms, mud and silt accumulate at the bottom, and anaerobic species of Clostridium, Desulfovibrio, etc. will flourish.
They produce gases. One gas, H2S, combines with lead or iron to give a precipitate which makes the mud black and the water poisonous.
Due to complete depletion of oxygen, the suspended bacteria die in their own waste products. There is hardly any life in water at this stage. The gas bubbles from .the anaerobes in the mud break the surface. Such processes lead to death of a river.
Microorganisms in Marine Water:
The marine water is high in salt and only halophilic organisms survive. Since temperature is very low, most of them are psychrophilic. Diatoms and protozoa as dinoflagellates are important components in food chain. In the offshore oceanic zone, photosynthetic organisms are present. These are diatoms and dinoflagellates.
Most marine microbes are found along the shoreline or littoral zone where nutrients are in abundance. Some unusual types are also present on the ocean floor in the benthic zone and even at the bottom of several miles-deep trenches, the abyssal zone.
In addition to the microorganisms inhabiting the different types of water, there are many pathogenic protozoa, bacteria, and fungi that are transmitted through water and cause serious diseases of humans and animals. However, pathogenic some important water-transmitted pathogenic microorganisms are given in Table 31.2.