Some Metabolic, Diversity and Toxicity Aspects of Bacterial Communities Life in Aquatic Sediments

Sediment is a special realm in aquatic environments and has high microbial diversity. Addition of organic electron donors to sediments stimulated heterotrophic activity. Bacteria utilize the more available fractions of the organic detritus in their own metabolism, leaving indigestible residues known as marine humus. Input of nitrogen and carbon from vegetated regions into freshwater sediments also stimulate aerobic, anaerobic and chemolithotrophic sediment microbes. Because bacteria respond dramatically to changes in their chemical environment, can be predicted rapid responses by the aquatic sediment microbial community to any change in plant species that affects sediment porewater chemistry. Temperature and rainfall can affect the some microorganisms growth and permanence such as E. coli and Enterococcus spp. The increase of pollutants load (e.g. Pb and Zn) in water can be expected with the reduction of flow, whereby the decrease of pathogens concentration can be due to high concentrations of metals (e.g. Hg and Pb) discharges in rivers. The enrichment of metals and nutrients concentration in sediments, especially in those with the fine texture, highlights that the adsorption process is the prevailing self-purification mechanism. Investigations of short-term variations of microbiological and chemical parameters in the water column have implied that, despite seasonal and daily variations, microbial standing stock biomass and activity in one and the same body of water do not change drastically from one day to the other. Marine sediments contain as much as 18 per cent organic matter and bacteria in bottom deposits may grow and multiply. Enteric bacteria may be concentrated in bottom sediments of rivers as a result of sedimentation of bacteria-bound particles. Although it has been demonstrated that microbial communities can affect chemical pollutants, the presence of toxicants can also affect microbial community structure.