ZoBell — 160 — Marine Microbiology 



and fatty acids. Besides playing the key role in the sulfur cycle in the sea, 

 sulfate reducers play an important role in the transformation of organic 

 matter. At least certain strains can utilize elementary hydrogen (see 

 page 109). In marine bottoms the hydrogen for this reaction probably 

 results from the anaerobic decomposition of organic matter. Issatchenko 

 (1914) noted the widespread occurrence of Desulfovihrio aestuarii in Arctic 

 Sea bottoms where he believed it was an important biochemical agent. 



The abihty of sulfate reducers to produce (Jankowski and ZoBell, 

 1944) and transform hydrocarbons (Tausson and Alioschina, 1932), the 

 almost universal presence of such bacteria in marine sediments both recent 

 and ancient (Bastin, 1926), their ability to function over a wide range of 

 environmental conditions, and the decreased sulfate content of oil-well 

 brines strongly suggest that sulfate-reducing bacteria are intimately asso- 

 ciated with petroleum genesis. Such bacteria are credited with being re- 

 sponsible for the formation of sulfur of the gypsum type (page 112). The 

 effect of sulfate reducers on iron corrosion is discussed by Starkey and 

 Wight (1943). 



Bavendamm (1932) noted the presence of large numbers of sulfate 

 reducers in calcareous mud around the Bahama Islands where he believed 

 they were instrumental in the precipitation of CaCOs under certain 

 conditions : 



CaSOl -I- 8 H -I- CO2 = CaCOs + 3 H2O -f- H2S 



In this reaction, organic matter serves as the hydrogen donor. Baven- 

 damm failed to take into account the acid that may result from the oxida- 

 tion of the organic matter, and that H2S itself is weakly acidic. 



The activities of sulfate-reducing bacteria are largely responsible for 

 the occurrence of H2S in stagnant bodies of water. The Black Sea is a 

 classical example of a large body of water in which few if any forms of 

 life except bacterial are possible at depths exceeding a few hundred meters 

 owing to the high concentration of H2S. Free oxygen is absent at depths 

 exceeding 200 meters (Sverdrup et al., 1942). Issatchenko (1924) found 

 vigorous sulfate-reducing bacteria in bottom samples from the Black Sea, 

 as did Ravich-Sherbo (1930). Similar conditions occur in Norwegian 

 fjords (Str9^m, 1939), the Caspian Sea (Butkevich, 1938), mud lakes or 

 limans of Odessa (Bunker, 1936), Lake Ritom in Switzerland (DtJGGELi, 

 1924), and many other bodies of water, both salt and fresh, having poor 

 vertical circulation. 



Copenhagen (1934) described an area approximately 25 by 200 miles 

 in the Atlantic Ocean off Walvis Bay, South Africa, where II2S is periodi- 

 cally liberated from bottom mud in quantities sufficient to be lethal to 

 flora and fauna in the overlying water. Sulfate-reducing bacteria were 

 isolated from the black mud. Incidentally, the mud contained no car- 

 bonate, thereby suggesting that in this area sulfate reduction promotes 

 the dissolution rather than the precipitation of CaCOs. The black mud 

 was rich in ferrous sulfide. 



Bunker (1936) attributed the blackening of mud and sand in certain 

 marine and lacustrine localities entirely to the action of sulfate-reducing 

 bacteria. According to Bunker, Issatchenko has reported the seasonal 

 production of H2S in the Sea of Azov in sufficient intensity to destroy 

 large numbers of fish and other aquatic animals. 



Whether sulfate reduction is a property of only one specific group of 

 bacteria or whether there are several types of organisms endowed with 



