714 Marine Microbiology 



bacteria, by destroying protein combinations, contribute to the re- 

 lease of various forms of nitrogen while sulphur bacteria are able 

 to transfer various reduced sulphur combinations into oxidized 

 ones containing ions of So"4. 



A similar type of the upper sediment layer is found in the 

 Azov Sea. In 1923, Isachenko, and then in 1937 a group of micro- 

 biologists under Butkevich, found denitrating, desulphurating 

 and thiobacteria in the Azov Sea upper sediment layer. 



Almost all of the enumerated physiological groups of micro- 

 organisms that were found in the upper sediment layer of the 

 North Caspian and Azov Seas belong to the group of autotrophic 

 microorganisms which do not need organic substance for their 

 development. Autotrophic microorganisms, however, constitute 

 only a small percentage of the total number of bacteria in water 

 basin sediments (8, 13). Therefore while considering the ques- 

 tion of transformation of organic substance, one should not con- 

 fine oneself to consideration of only those groups that "complete" 

 the processes of decomposition (by transforming CH^, H2, HjS, 

 CO2). 



To get an idea of the intensity of bacterial biochemical ac- 

 tivities on the surface of sediments one should be aware not only 

 of the qualitative composition of separate groups but also of the 

 total number of microorganisms inhabiting sediments and their 

 weight, i.e., biomass. 



The number of bacteria in sediments is great: in the Azov 

 Sea in July it fluctuated from 6.3 x 10^ to 17.2 x 10^ cells per g 

 of natural silt; the biomass varied from 17 to 57 g/m^/cm layer 

 (16). 



In July of 1951 and 1952, high concentrations of microor- 

 ganisms in silts were also observed in the North Caspian Sea. In 

 the area of the approaches to the Volga river delta the number 

 of microorganisms was found to have reached 12 x 10^ per gm 

 of natural silts soon after the highflood. The biomass changed at 

 this time from 2-6 g/m^ to 50-52 g/m^/cm layer ( 15 ) . 



According to the data found in literature, a bacterial cell 

 expends for the fomiation of its body, an amount of organic sub- 

 stance exceeding its own weight by three fold. Consequently, 

 three times as much organic substance was consumed in the for- 



