ZoBell — 142 — Marine Microbiology 



rate of utilization was relatively independent of the oxygen tension. After 

 the supply of dissolved oxygen was depleted or was reduced to such a low 

 level that oxygen could not be replaced by diffusion as rapidly as it was 

 consumed by respiring bacteria, the oxidation of lignin was retarded. The 

 rate of oxidation of organic matter in sea water, as indicated by oxygen 

 consumption, was found to be independent of the oxygen tension within 

 the examined range of 0.43 to 17.8 mgm./L. 



Proteinaceous compounds : — As a class, marine bacteria are actively 

 proteolytic. They rapidly decompose most simple proteinaceous com- 

 pounds, and even the most complex compounds are slowly attacked with 

 the liberation of ammonia and CO2. Every one of tiie 60 pure cultures 

 studied by ZoBell and Upham (1944) liberated ammonia from peptone, 

 47 of them liquefied gelatin, and half of them hydrolyzed casein. Mixed 

 cultures from mud or sea water break down peptone, gelatin, and casein 

 with the production of CO2 as well as ammonia. 



According to Trask (1934), amino acids and simple proteins consti- 

 tute a very minor part of the organic content of marine sediments. This 

 is ascribable to the tendency of bacteria to decompose such compounds, 

 which constitute an appreciable part of the protoplasm of plants and an- 

 imals. Complex nitrogenous compounds are more abundant in sediments 

 than are simple proteins, but neither simple nor complex proteins are 

 proportionately as abundant in sediments as in the organic matter of 

 plant and animal tissues. Waksman (1933) believes that lignoproteins 

 and hemicellulose-protein complexes account for about 75 per cent of the 

 organic nitrogen content of sediments. 



Hecht (1934) reports that most simple proteins are completely de- 

 composed in marine sediments even under anaerobic conditions. Decom- 

 position of the bodies of marine invertebrates, birds, and mammals was 

 observed to be most rapid in sea water containing dissolved oxygen. The 

 presence of HoS and reducing conditions inhibited the decomposition of 

 proteins. About 90 per cent of the combined nitrogen content of deeply 

 buried sediments was present in chitin. 



The author is aware of no systematic investigations on marine proteo- 

 lytic bacteria, although many investigators refer to the ability of marine 

 bacteria to liquefy gelatin, utilize peptone, and to decompose fish muscle 

 or the nitrogenous tissues of other marine animals. For example, 

 Schmidt-Nielsen (1901) was impressed by the rapidity with which bac- 

 teria from Oslo Fjord decomposed proteins with the liberation of am- 

 monia. He remarked that, although pouring sea water over boiled 

 shrimps renders them temporarily more attractive in appearance, the 

 shrimps are soon decomposed subsequently by bacteria from the sea 

 water. 



Proteolytic bacteria are primarily responsible for the spoilage of fish, 

 shellfish, crab meat, and other marine food products. Although not based 

 upon quantitative studies, the opinion is rampant that marine fish are 

 more susceptible to spoilage than fresh-water fish. Possibly marine bac- 

 teria may be more actively proteolytic than corresponding fresh-water 

 flora; there may be differences in the composition of fish from different 

 environments; marine bacteria may be active at temperatures somewhat 

 lower than fresh-water bacteria as a group, or there may be other explana- 

 tions to account for this opinion. 



Fish and other marine food products soon show signs of spoilage if 



