220 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



hydrogen sulfide or sulfur, (3) formation of nitrate, 

 (4) assimilation of ammonia, or (5) the liberation 

 of phosphate from organic compounds are micro- 

 bial processes that tend to decrease the pH of 

 their environment. Reactions ranging from pH 

 6.8 to 8.7 in Gulf coast sediments are believed to 

 be attributable, at least in part, to microbial 

 activities. Similarly, bacteria and allied micro- 

 organisms are believed to be the principal dynamic 

 agencies that create conditions in marine sediments 

 sometimes as reducing as En— 460 millivolts 

 (ZoBe.U 1946b). 



The general tendency is for micro-organisms to 

 mineralize the organic remains of plants and ani- 

 mals in marine sediments. In highly reducing 

 environments, however, the microbial decomposi- 

 tion of organic matter may result in residues 

 relatively richer in hydrogen and correspondingly 

 poorer in oxygen, nitrogen, sulfur, and phosphorus. 

 This results in the accumulation of organic com- 

 plexes that are more petroleum-like than then- 

 predecessors (ZoBell 1950b). The microbial for- 

 mation of methane is a common property of recent 

 marine sediments, and there is pretty good evi- 

 dence that bacteria also produce higher hydro- 

 carbons. Wliile there is no reason to believe that 

 bacteria produce petroleum, they may contribute 

 in many ways to its formation. The high organic 

 productivity and rapid rate of sedimentation in 

 Gulf coast waters suggest this region as a potential 

 source bed of petroleum. 



Petroleum hydrocarbons may be modified in 

 recent sediments by micro-organisms. Both aero- 

 bic and anaerobic bacteria which attack petroleum 

 hydrocarbons were detected in nearly all 1-gram 

 samples of surface mud collected from shallow 

 water along the coasts of Louisiana and Texas. 

 From hundreds to millions of such micro-organisms 

 per gram of mud were demonstrated by the 

 minimum dilution method. 



Sulfate-reducing bacteria were also found in 

 abundance, some at core depths exceeding a 

 hundred feet. Sulfate reducers form hydrogen 

 sulfide, and they may account for the formation 

 of sulfur. The recovery of sulfate reducers liaving 

 unique tolerance for temperature, salinity, and 

 hydrostatic pressure from oil and sulfur wells 

 suggests that they may be indigenous species in 

 ancient marine sediments (ZoBell and Rittenberg 

 1948). A large percentage of the sulfate reducers 



isolated from Gulf coast sediments can utilize 

 molecular hydrogen (Sisler and ZoBell 1950). 



Several other physiological types of bacteria, 

 that may function as geochemical agents, have 

 been found in marine sediments, but their impor- 

 tance can be assessed only after they have been 

 more thoroughly studied. 



Marine fungi, including yeasts and molds, are 

 found almost exclusively in water and the topmost 

 layers of sediment. Being heterotrophs, such 

 fungi are closely associated with organic sub- 

 stances. Both yeasts and molds commonly occur 

 growing either saprophytically or parasitically on 

 marine plants and animals. According to Sparrow 

 (1936), who isolated 18 new species of mold fungi 

 from the Woods Hole region, marine fungi have 

 been even less completely studied than marine 

 bacteria. Barghoorn and Linder (1944) were 

 impressed by the diversity of fungi found in the 

 sea. A good many of the fungi species isolated 

 from the sea are quite unlike any known terrestrial 

 species. They grew better in sea water than in 

 corresponding fresh water media, and some 

 species developed in media containing three times 

 as much salt as normal sea water. 



LITERATURE CITED 



Atkins, W. R. G., and Warken, F. J. 



1941. The preservation of fishing nets, trawl twines, and 

 fiber ropes for use in sea water. Jour. Mar. Biol. 

 A.SS0C. 25: 97-107. 

 Baier, C. R. 



1935. Studien zur Hydrobakteriologie stehender Binnen- 

 gewasser. Arch. f. Hydrobiol. 29: 183-264. 

 Barghoorn, E. S., and Linder, D. H. 



1944. Marine fungi: their taxonomy and biology. 

 Farlowia 1 : 395-467. 

 Bavendamm, W. 



1932. Die mikrobiologische Kalkfallung in der tropis- 

 chen See. Arch. f. Mikrobiol. 3: 205-27G. 



Beneckb, W. 



1933. Bakteriologie des Meeres. Abderhalden's Hand, 

 d. biol. Arbeitsmethoden, IX Abt. 5: 717-854. 



Berkeley, C. 



1919. A study of marine bacteria. Straits of Georgia, 



B. C. Trans. Roy. Soc. Canada, Ser. 3, Sec. 5, 13: 



15-43. 

 Burke, V. 



1934. The interchange of bacteria between fresh water 

 and the sea. Jour. Bact. 27: 201-205. 



Burke, V., and Baird, L. A. 



1931. Fate of fresh-water bacteria in the sea. Jour. 

 Bact. 21: 287-298. 

 Campbell, L. L., and Williams, O. B. 



1951. A study of chitin-decomposing micro-organisms 

 of marine origin. Jour. Gen. Microbiol. 5: 894-905. 



