218 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Quantitative data on the relative amounts of 

 organic matter synthesized by autotrophic bacteria 

 are not available, but judging from the abundance 

 of such bacteria and the quantities of ammonia, 

 hydrogen, methane, or other substance believed 

 to be oxidized, organic production from this source 

 may be appreciable. 



The chief fimction, however, of bacteria in the 

 marine environment is in the mineralization or 

 modification of organic matter (Waksman 1934). 

 Among the organic materials found to be attacked 

 by marine micro-organisms are sugars, starches, 

 celluloses (Bavendamm 1932; Waksman et al., 

 1933), pectins, glucosides, fatty acids (Thayer 

 1931), triglycerides, alcohols, sterols, proteins, 

 amino acids, chitins (Hock 1940), lignins, agar 

 (Stanier 1941; Humm 1946), and hydrocarbons 

 (ZoBell 1950a). These organic substances are 

 attacked by both aerobic and anaerobic bacteria. 



From Gulf of Mexico mud, Campbell and 

 Williams (1951) isolated 20 strains of aerobic 

 chitin-decomposing bacteria, including species of 

 Achromobacter, Flavobacterimn, Micrococcus, and 

 Pseudomonas. Several of the cultures were 

 actively proteolytic and/or lipolytic. 



Mixed cultures from marine mud tend to de- 

 compose the organic remains of plants and animals 

 (Waksman 1934) in aerobic environments with 

 the formation of carbon dioxide, ammonia, sulfate, 

 phosphate, and other oxidation products at a 

 rate which is primarily a function of the tem- 

 perature. In the absence of free oxj-gen the rate 

 at which organic matter is modified by bacteria 

 may be much slower, and, while there may be 

 much mineralization of organic substances, in 

 anaerobic environments certain constituents may 

 be reduced or hydrogenated to form the mother 

 substance of petroleum (ZoBell 1950b). 



The action of heterotrophic bacteria is not 

 confined to the decomposition of particulate or- 

 ganic materials. Dissolved organic matter is 

 also utilized, it having been shown by ZoBell and 

 Grant (1943) that under static conditions bacteria 

 may reduce the organic content of sea water to 

 less than 0.1 mgm./L. According to Waksman 

 and Carey (1935), roughly 60 percent of the organic 

 carbon is oxidized by aerobes to carbon dioxide 

 and the remaining 40 percent is assimilated for 

 conversion into bacterial protoplasm. The latter, 

 being particulate, becomes available as a source 



of food for protozoa, copepods, filter feeders, 

 detritus feeders, and grazing animals in general. 



Ki-izencky and Podhradsky (1927) regard the 

 conversion of dissolved organic matter into par- 

 ticulate matter utilizable by animals as one of 

 the most important functions of bacteria in aquatic 

 environments. The importance of bacteria as 

 food for animals has been emphasized by the work 

 of Baier (1935), MacGinitie (1935), Voroschilova 

 and Dianova (1937), Mare (1942), and ZoBell 

 and Feltham (1938). The latter workers (1942) 

 estimated that around 10 grams (dry weight) of 

 bacterial organic matter is produced per day per 

 cubic foot of mud in a shallow marine mud flat. 

 In summarizing the ecological function of bacteria 

 on sand beaches, Pearse et al. (1942) point out 

 that besides serving as food for small animals, 

 bacteria are important scavengers, and they pro- 

 duce plant nutrients, including ammonia, nitrite, 

 nitrate, and phosphate. From thousands to 

 millions of living bacteria were found in beach 

 sands at Beaufort, North Carolina. 



Large numbers of bacteria were found by 

 Williams et al. (1952), to be associated with 

 the bay shrimp, Penaeus setiferus, taken from 

 Aransas Bay and from the Gulf in the region of 

 Galveston. Species of Achromobacter, Bacillus, 

 Micrococcus, Pseudomonas, Alcaligenes, and Flavo- 

 bacterium predominated in the order named. 

 Most of the attached bacteria were carried by 

 the cephlothorax portion of the shrimp. The 

 optimum temperature for the growth of the 

 bacteria was around 25° C, but most of the 1,200 

 cultures examined grew slowly at 4° C. Neither 

 coliforms nor enterococci were detected by 

 Williams and Rees (1952) in the intestinal tract 

 of shrimp, suggesting that such bacteria have 

 sanitary significance. 



Another important function of bacteria is as 

 sjonbionts in the alimentary canal of most marine 

 animals where they aid m the digestion of chitin, 

 cellulose, pectin, lignin, and other organic com- 

 plexes. Similarly, certain shipworms and wood 

 borers are believed to depend upon commensal 

 bacteria which help to digest cellulose and lignin. 



On the other hand, a small percentage of the 

 microbial flora is pathogenic for plants or animals. 

 Fish, Crustacea, shellfish, and other marine ani- 

 mals in nearly all stages of development may be 

 susceptible to microbial infections; the pertinent 



