Bacteria in bottom sediments

The previous section dealt with the role of bacteria as producers of biomass in the open water. In this section the use of organic substrates in bottom sediments is also considered. 

Fenchel and Jorgensen (1977) considered a hypothetical detritus feeder which ingests detrital particles as large as about 200 ixm. This detritus feeder will ingest about 4 mg of bacteria, 5 mg of flagellates, 0.5 mg of ciliates and some other protozoans per gram of consumed detritus. This means that not 

Bacteria only assimilate dissolved substrates solid substrates are first hydrolysed by extracellular enzymes before being assimilated. Degradation of detritus starts with hydrolytic cleavage of the particulate material into small molecules which can be assimilated by the bacteria. The end-products of extracellular hydrolysis are most amino acids, mono- and disaccharides, and long-chain fatty acids. In aerobic environments these are taken up directly by heterotrophic bacteria, and further metabolism is intracellular. A variable fraction of the detritus in marine ecosystems is never completely remineralised, but accumulates mainly within the anoxic environment, and is gradually transformed into organic complexes refractory to microbial attack (Fenchel and Jorgensen, 1977). 

Recently the ATP method has been employed to determine the total biomass of bacteria, micro- and meiofauna and microphytes in sediments. In 

In contrast to the results obtained from bacteria and small algae, Karl et al. (1978) found that the C/ATP ratios in multicellular organisms (copepods, isopods and worms) were less than 100, as compared with a ratio of 250 commonly found in microorganisms. 

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Cappenberg, T.E., 1974b. The interrelations between sulfate-reducing and methane-producing bacteria in bottom sediments of a fresh water lake. II. Inhibition experiments. Antonie van Leeuwenhoek J. Microbiol. Serol., 40 297—306. 

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