A large number of microorganisms both saprophytes and pathogens are found in water which fall under the groups bacteria, fungi, algae, protozoa and nematodes. Several animal viruses are also transmitted through water.
The majority of bacteria found in water belongs to groups: fluorescent bacteria (Pseudomonas, Alginomonas ,etc.), chromogenic rods (Xanthomonas, etc.), coliform group (E.coli, Aerobacter, etc.). Proteus group, non-gas forming, non-chromogenic and non-spore forming rods, spore formers of the genus Bacillus, and pigmented and non-pigmented cocci (Micrococcus).
Marine microbiology deals with microorganisms living in sea. About 97% of earth's water is present in sea. Ocean at its depth is slightly more than 11,000 meters deep. Therefore, pressure in the marine environment increases by 1atm/10 meters in depth. The bacteria growing in vertically differentiated marine environment can be categorized in three groups: a. barotolerant (bacteria growing between 0 and 400 atm but best at normal atmospheric pressure), b. moderate barophiles (bacteria growing optimally at 400 atm, but still grow at 1 atm), and c. extreme barophiles (bacteria growing only at higher pressure i.e. 6000 to 11,000 meter depth). The hydrostatic pressure can reach 600 to 1,100 atm in the deep sea, whereas the temperature is about 2 to 3ºC. Increased pressure does not affect the barotolerants. Some bacteria living in gut of deep sea invertebrates ( amphipods and holothurians) and are truly basophilic. These basophilic bacteria play a significant role in nutrient cycling.
In the marine system, the major source of organic matter is from phytoplanktons (phyto, plant and planktons wandering) i.e. free floating plants. A common planktonic alga is Synecococcus which can reach to a density of 104 to 105 cells/ml at the ocean surface. Picocyanobacteria (very small cyanobacteria) may represent 20 to 80% of total phytoplankton biomass. In turn these act as a source of food for marine fish and other animals.
It has been found that about 1/3 of oceanic picoplanktons (cell > 2µm) are archaebacteria( group of bacteria) associated with hostile environment i.e. hot springs, deep marine " black smoker" areas, saline and termoacidophile region).
Lakes and river provide the major fresh water bodies which are used for potable water. However, due to growth of phytoplanktons and decomposition of organic matter nutrient status varies throughout the year. In addition, animal activities (including man) also influence the nutrient level of lakes and rivers. The nutrient-poor lakes are known as oligotrophic lakes, whereas the nutrient rich lakes are called eutrophic lakes. The nutrient rich lakes contain high amount of bottom sediments containing organic matter. Eutrophication (enrichment of lake due to high concenteration of nutrients) of lakes occur by multifarious ways where anthropogenic activities are of much important size. The eutrophic lakes support luxuriant growth of bacteria and algae. Some of the fast growing algae at optimum condition bloom well showing their maximum population. This phenomenon is known as water blooming, and microorganisms associated with it are called water blooms.
The microorganisms growing in lakes are the genera Anabaena, Microcystis, Nostoc, Oscillatoria, Oedogonium, Spirulina, diatoms, protozoa, etc.
The capacity of rivers and streams to process the added organic materials is limited. If too much organic material is added, the water becomes anaerobic. This situation arises in those rivers and lakes which are present near the urban areas. In streams and rivers untreated or inadequately treated municipal wastes and other organic materials are discharged. These organic wastes cause changes in microbial community. Release of organic wastes from known sources is called point source of pollution. When the amount of organic materials added is not too high, it supports the growth of several algae. Algae produce O2 during photosynthesis in day light and evolve CO2 in day and night. This results in diurnal oxygen shifts. The demand of oxygen is expressed in terms of biological oxygen demand (BOD) or the chemical oxygen demand (COD).
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