Aquatic microbiology

Aquatic microbiology is the study of microorganisms and there activities in fresh, estuarine, and marine water, including springs, lacks, rivers, bays, and seas. It may also be added that it is the study of the microorganisms – viruses, bacteria, algae, protozoa, and microscopic fungus which inhabit that natural waters.

Natural Water

A process known as the water cycle or hydrologic cycle maintain the earth’s moisture in continuous circulation. It has been estimated that about 80,000 cubic miles of water from ocean and 15,000 cubic miles from lacks and land surface evaporate annually. Total evaporation is equaled by the total precipitation. Of which around 24,000 cubic miles fall on land surface. 

Microorganisms of various kinds are present at different stages of this cyclic process – in atmospheric water, surface water, and ground water.

Atmospheric Water

The moisture contained in clouds and precipitated as snow, sleet, hail, and rain constitutes atmospheric water. The microbial flora of this water is contributed by the air. In effect, the air is washed by atmospheric water, which carries with it the particles of dust to which microorganisms are attached. Most of the microorganisms are removed from the air at the early stages of precipitation.

Surface Water

Bodies of water such as lakes, streams, river, and oceans represent surface water. To a greater or lesser degree, these water are susceptible to contamination with microorganisms from atmospheric water (precipitation), the surface runoff from soil, and any wastes deliberately dumped into them. Microbial population vary in both number and kind with the source of water, with composition of the water in terms of microbial nutrients, and with geographical, biological, and climatic conditions.

Ground Water

Ground water is a subterranean water, occurs where all pores in the soil or rock containing materials are saturated. Bacteria as well as suspended particles are removed by filtration, in varying degrees, depending upon permeability of the soil and depth to which the water penetrates.

The Aquatic Environment

The microbial population in a body of natural water is, to a large extent, determined by the physical and chemical conditions which prevail in that habitat. Some of these conditions are discussed here.


The temperature of surface water varies from 0°C in polar reason to 30 to 40°C in equatorial regions. More then 90% of the marine environment is below 5°C, a condition favorable for the growth of psychrophilic microorganisms. Microorganisms are also found in natural hot water springs where temperature as high as 75 to 80°C. 

Recently microbiologists has reported extreme thermiophilic microorganisms associated with geothermal vents in the pacific ocean floor. These unusual microorganisms are capable of growing at 250°C and 265 atm of pressure.

Hydrostatic Pressure

Hydrostatic pressure differ in surface water and of the water in oceanic depths. Hydrostatic pressure affects chemical equilibrium, solubility of nutrients such as bicarbonate. Hydrostatic pressure also increases the boiling point of water, thereby maintaining water in its liquid state at high temperature and pressure.

By definition hydrostatic pressure increases with depth at the rate of 1 atm per 10 meter. 

Barophilic microorganisms, organisms those cannot grow on normal atmospheric pressure, have been isolated from pacific trenches (depth 1000 to 10,000 m), where enormous hydrostatic pressures exist (> 100 atm).


Most form of aquatic life depends, directly or indirectly, upon the metabolic products of photosynthetic organisms. In most aquatic habitats these primary products are algae, and their growth is restricted to the upper layers of water through which light can penetrate.The depth of photic zone varies depending on such local conditions as latitude, season, and particularly the turbidity of the water.

Generally phototrophic activity is recorded from 50 to 125 m.

Carbon dioxide is available largely form HCO3, although some gaseous CO2 is also available.

Reference: Microbiology by Pelczar

Gaurav Singh

Editor in Chief Medical Microbiology & RDT Labs - RDT Labs Magazine | BSc Medical Microbiology | MSc Microbiology

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