598 KAPLAN AND RITTENBERG [CHAP. 23 



Furtlier, a smaller number of molecules are susceptible to attack under anaerobic 

 conditions. 



Complex carbohydrates, lipids and proteins, which may be either totally 

 insoluble or only minutely so, are degraded. For example, agar, cellulose, long- 

 chain fatty acids and gelatin are readily solubilized under both aerobic and 

 anaerobic conditions. More stable substances, such as keratin and lignin, 

 appear to require aerobic conditions and only select flora will attack them. 

 The lignins appear to be the most stable of the common organic polymers 

 (Wallentyne, 1957; ZoBell, 1946). This is seen from the fact that marine humus 

 may contain from three to four times as much lignin as the phytoplankton 

 (W'aksman, 1933), and lignin accumulated in fresh water is considered as the 

 source material for coal. 



It must be understood that the marine environment, like the lacustrine 

 environment and soils, has a tremendously adaptable and interdependent 

 microbial flora, each preparing the environment for their associates. Thus, one 

 particular set of organisms may be capable of hydrolyzing the bonds of a 

 complex molecule, such as cellulose, and breaking it down to the individual 

 sugars. Others may convert the sugars to carboxylic acid, which may in turn be 

 ultimately oxidized to CO 2 or reduced to methane and hydrogen. In turn auto- 

 trophic bacteria may assimilate the end products of heterotrophic catabolism 

 and either convert them back to complex organic matter or use them for their 

 own energy -generating processes. The associations may extend to higher forms : 

 thus vitamins essential to animals may be generated by bacterial metabolism. 



b. Types and numbers 



The types of bacteria present in marine sediments are essentially the same in 

 terms of biochemical potential at least as those found in lake muds or soils. 

 Very often the establishment of the presence of a particular organism is directly 

 proportional to the effort undertaken in finding it. 



It is recognized that the mud-water interface is the richest zone for microbial 

 proliferation; it is here that a continual supply of nutrients, organic matter, 

 oxygen, etc. is being provided and toxic end products removed. Bacterial 

 coimts range from 10^ to lO^/ml on an average for the bottom water and surface 

 sediment as compared with 10^ to 10^ for the photosynthetic zone (ZoBell, 

 1959). 



The bacterial coinit in the sediments drops rapidly in the first 10 to 20 cm 

 from the surface and more slowly thereafter. The bacterial counts vary greatly 

 according to the environment. In the North Pacific Ocean, lO^/g of sediment 

 have been reported (Kriss and Rukina, 1952); comparable populations have 

 been detected by Rittenberg (1940) and by Emery and Rittenberg (1952) in 

 sediments in the southern California basins. Actually, it is the sediment type 

 rather than geographical location that determines nmnbers. 



It is often assumed that stagnant waters and underlying sediments contain a 

 restricted and impoverished microbial flora. However, Kriss (1959) reported 



