Peculiarities of Water as an Environmental Habitat for Microorganisms

Abstract

As a habitat for the existence of microorganisms, water has properties not found in other natural microbial habitats such as soil, and plant and animal bodies; indigenous aquatic microorganisms are adapted to these conditions. Natural waters are generally low in nutrient content (i.e., they are oligotrophic); what nutrients there are, are homogeneously distributed in the water. The movement of water freely transports microorganisms; to counter this and offer themselves some protection, many aquatic organisms are either stalked or arranged in colonies immersed in gelatinous materials. To enable free movement in water, many aquatic microorganisms and/or their gametes have locomotory structures such as flagella. Microorganisms are often adapted to, and occupy particular habitats in the water body; some occupy the air–water interphase (neuston), while others live in the sediment of water bodies (benthic). The conditions which affect aquatic microorganisms are temperature, nutrient, light, salinity turbidity, water movement. The methods for the quantitative study of aquatic microorganisms are cultural methods (plate count and MPN), direct methods (micro­scopy and flow cytometry), and the determination of microbial mass. The microscopy methods are light (optical), epi-flourescence, confocal laser scanning microscopy, transmission electron microscopy, and scanning electron microscopy. Microbial mass may be direct (weight after oven-drying) or indirect (turbidity, CO₂ release, etc).