Chapter XII — 159 — Sulfur Bacteria 



Little is known concerning the bacterial decomposition of organic 

 sulfates, sulfonates, and related compounds. Under aerobic conditions 

 the sulfur is probably liberated as suUite or sulfate. 



Sulfate reduction : — Bacteria which reduce sulfate are abundantly 

 and widely distributed in the sea. ZoBell (1938a) demonstrated from 

 1000 to 10,000 sulfate reducers per gram of marine mud. Rittenberg 

 (1941) found sulfate reducers in each of several hundred samples collected 

 at various stations off the coast of California and in the Gulf of California. 

 They were found at all water depths and core depths from which samples 

 were taken. Sulfate reducers were only rarely present in sea water except 

 near the bottom. 



Although earlier workers had postulated that the bacterial reduction of 

 sulfate is responsible for the accumulation of sulfide in marine bottoms, 

 Zelinski (1893) was the first to claim the isolation of sulfate-reducing 

 bacteria. From Black Sea mud he isolated organisms which he designated 

 Vibrio hydrosulfureus and Bacterium hydrosulfureum ponticum which re- 

 duced sulfate, sulfite, and thiosulfate to H2S. His descriptions of the or- 

 ganisms suggest that he was working with mixed cultures. Actually it is 

 rather diflicult to obtain pure cultures of sulfate reducers. 



Beijerinck (1895) carefully described Spirillum desulfuricans, sl sul- 

 fate reducer which he isolated from Delft ditch water. He predicted the 

 absence or paucity of sulfate in the deeper layers of soil in Holland due to 

 the activity of the sulfate reducer. A similar organism named Spirillum 

 aestuarii was isolated from North Sea coast water and mud by van Del- 

 den (1904). Sp. aestuarii required sea water or 3 per cent NaCl for its 

 growth, whereas Sp. desulfuricans was not active in 3 per cent NaCl 

 media. 



After finding that these two organisms, as well as Elion's Spirillum 

 thermodesulfuricans, could be acclimatized to tolerate different salinities 

 and temperatures, Baars (1930) regarded all three organisms as strains 

 of a single species which he called Vibrio desulfuricans. However, Ritten- 

 berg (1941) was unable to adapt the strain which he isolated from the sea 

 to grow in fresh water or to grow at temperatures exceeding 40° to 45° C. 

 (The optimum temperature for growth of Sp. thermodesulfuricans is 55° 

 C). Likewise the marine sulfate reducer could not be induced to form 

 spores, unlike the organism studied by Starkey (1938), and no sporoge- 

 nous marine sulfate reducers have been found. 



Starkey (1938) isolated a sporogenous sulfate reducer from soil which 

 was indistinguishable from Vibrio desulfuricans. He induced an asporo- 

 genous strain of the latter to form spores and acclimatized it to grow at 

 from 50° to 55° C, whereupon he proposed Sporovibrio as the generic name 

 of the sulfate reducers. In the absence of adequate confirmation of 

 Starkey's observation and since spore formation does not seem to be a 

 primary or constant characteristic of sulfate reducers, the generic name 

 Desulfovibrio is provisionally applied to previously described species of 

 sulfate reducers in the sixth edition of the Bergey (1946) Manual. Un- 

 questionably there are sporogenous sulfate reducers, but it has not been 

 established that all sulfate reducers form spores. 



The absence of free o.xygen, the presence of sulfate, and the presence of 

 organic matter are the chief requirements for the activity of sulfate-reduc- 

 ing bacteria, x^pparently there are strains which utilize nearly any kind 

 of organic matter including proteins, sugars, starches, hydrocarbons, fats, 



