ZoBell — 162 — Marine Microbiology 



oxidize sulfur or its compounds in the sea. In order to facilitate an under- 

 standing of the confusing terminology in the literature, an attempt is made 

 to combine the essential features of various classifications proposed by 



WiNOGRADSKY, MOLISCH, OrLA-JeNSEN, BuCHANAN, BaVENDAMM, ElLIS, 



VAN NiEL, and others. 



Achromic sulfur bacteria : — Bacteria of the Thiobacillus group oxidize 

 sulfide, elementary sulfur, thiosulfate, or tetrathionate. Some of those 

 which oxidize H2S or other sulfides often deposit sulfur extracellularly, 

 although sulfate is generally the end product of their oxidative metabo- 

 lism. Several strains of Thiobacillus have been found in water. 



Nathansohn (1902) isolated Thiobacillus thioparus from sea water. 

 It grew in sea water enriched with either potassium sulfide or sodium 

 thiosulfate without a source of organic carbon. A little organic matter 

 did not inhibit its development. It failed to grow in the absence of CO2 

 and carbonate. In the presence of an abundance of sulfide, the latter was 

 oxidized to sulfur and deposited extracellularly. Though able to oxidize 

 elementary sulfur, it prefers sulfide, thiosulfate, or tetrathionate. The 

 form of sulfur oxidized and the end products of oxidation depend upon the 

 concentration of reactants and certain environmental conditions includ- 

 ing the ^H and Eh. Thiobacillus thioparus appears to be widely distrib- 

 uted in coastal waters, marine mud, fresh water, and soil (Bunker, 1936). 



Beijerinck (1904), who found Thiobacillus thioparus in the sea off the 

 Dutch coast, reported that it oxidizes thiosulfate to sulfate and desposits 

 sulfur : 



2 SaOa— -F O2 = 2 SO4— + 2 S 



Tetrathionate was oxidized less readily to sulfate and free sulfur: 



S4O6— + O2 = 2 S04~ -1- 2 S 



Ravich-Sherbo (1930) ascribed the absence of H2S in certain zones in 

 the Black Sea to the activities of Thiobacillus thioparus: 



2 H2S + 5 O2 = 2 S04~ -I- 2 H2O 



Large numbers of Thiobacillus thioparus were noted in poorly oxygenated 

 laminae or zones of the Black Sea which received H2S produced by sul- 

 fate-reducing bacteria. 



Thiobacillus denitrificans is often found in mud, water, and soil. Is- 

 SATCHENKO (1914) noted its occurrence in Arctic Seas along the Murman 

 coast of northern Russia. It is an anaerobe which utilizes nitrate as hy- 

 drogen acceptor while oxidizing sulfide or elementary sulfur : 



S H2S -h 2 HNO3 = 5 S -I- N2 -F 6 H2O 



Thiobacillus thiooxidans oxidizes elementary sulfur to sulfate : 



S + 2 O2 = SO4 — 



Conditions in the sea do not seem to be conducive to the growth of this 

 organism, although Saslawsky (1927) isolated obligately halophilic 

 strains from Russian mud lakes. 



According to Ellis (1932), Thiobacillus thiogenes (Molisch) and 

 Thiobacillus bovisla (Molisch) are exclusively marine species. The latter 

 probably belongs to another genus, since its cells contain sulfur granules. 



The Achromatiaceae and Beggiatoaceae have been called Leucothio- 



