ZoBell — 166 — Marine Microbiology 



water sulfureta are all very much alike. Sulfur bacteria appear to be 

 independent of salinity over a range of 0.05 to 7.5 per cent NaCl. The 

 purple forms prefer diffuse or subdued sunlight and a low oxygen tension. 

 They require H2S which, in sulfureta, is provided largely by sulfate re- 

 ducers. 



Baas Becking (1925) described a sulfur etum as a natural ecological 

 community of bacteria operative in the sulfur cycle. It is a biocoenosis 

 of sulfate-reducing bacteria and H2S-oxidizing bacteria of various kinds 

 along with several other kinds of microorganisms. In the fresh water, 

 brine, and brackish water which he studied, Chromatium and Beggiatoa 

 were commonest, followed by Lamprocystis, Amoebohacter , Thiothrix, Thi- 

 opedia, Thiopolycoccus, and Thio spirillum. Protozoans feeding on sulfur 

 bacteria were common. Euglena and Phacus of various types, Oscilla- 

 toria, Phormidium, and many diatoms were usually present. The green 

 algae were represented by a Protococcus-\ike form. Nematodes and a 

 large Spirochaete were observed. Baas Becking found green bacteria in 

 brackish water but not in brine. 



Chlorobacteria, or green sulfur bacteria, have been found in the sea, 

 especially in brackish water. Although reference has been made to them 

 for more than half a century, agreement concerning their physiology and 

 taxonomic position is still lacking. According to van Niel (1931), Chloro- 

 biuni li?nicola is the only strain which has been obtained in pure culture, 

 although Chlorobacterium, Cyanodictyon, Pelodictyon, and possibly other 

 genera have been named. 



Nadson (191 2) described Chlorobium limicola which he found in brack- 

 ish water and bottom mud in the Baltic, Black, and Caspian seas, as well 

 as in the salt Lake Weissowo. He thought they were minute algae. 

 Benecke (1933), who found green bacteria in the Baltic Sea, relates that 

 Pascher designated them as small Protococcales. However, as van Niel 

 (193 1) pointed out, bacteriochlorin, the green pigment of Chlorobium 

 limicola, differs from the chlorophyll of algae. Moreover, these bacteria 

 assimilate H2S in subdued sunlight and deposit sulfur extracellularly, 

 therein resembling the purple Athiorhodaceae : 



2 H2S + CO2 = (CH2O) -f H2O -I- 2 S 



Transformation of selenium compounds : — The close analogy between 

 the chemical behavior of sulfur and selenium provided the incentive for 

 Brenner (191 6) to investigate the effect of bacteria upon selenium com- 

 pounds. He isolated an organism. Micrococcus selenicuSy from marine 

 mud at Kiel which autotrophically oxidized selenide: 



2 HaSe -I- 5 O2 = 2 Se04— + 2 H2O 



It also oxidized selenite to selenate. When organic matter was added to 

 the medium and oxygen excluded. Micrococcus selenicus reduced selenite 

 and selenate as well as thiosulfate. Thiobacillus thioparus, which Bren- 

 ner isolated from the mud, failed to utilize selenium compounds. 



Neither selenate nor tellurate was reduced by Desulfovibrio aestuarii 

 studied by Rittenberg (1941). 



