428 Marine Microbiology 



bility. These observ^ations afford some reconciliation of tlie find- 

 ings of Baars (2) with those of Rittenberg (21). 



Whetlier or not the name aestuarii is accepted for the com- 

 mon marine type of Desulfovibrio, there is Httle doubt that the 

 types are physiologically and morphologically similar. Both differ 

 substantially from the two sporulating species of sulphate-re- 

 ducing bacteria: the thermophile Clostridium nigrificans (earlier 

 Vibrio, Sporovihrio or Desulfovibrio thermodesulfuricans) and 

 the mesophilic Desulfovibrio orientis. It is a curious fact that, 

 to the authors' knowledge, marine stiains of the two sporulating 

 species have not been reported formally in the scientific litera- 

 ture. One of us in collaboration with Professor C. B. van Niel 

 and the late Miss M. E. Adams sought thermophiles from a 

 marine environment, and indeed obtained enrichments of a con- 

 ventional kind from the bay of Monterey (near Elkhorn Slough) 

 showing blackening at 55° in saline media. Despite many efforts, 

 including micro-manipulation and multiple colony isolations, a 

 pure culture was not obtained; the crude culture contained or- 

 ganisms morphologically similar to CI. nigrificans but since the 

 maximum sulphide content of the cultures was low (c 30 mg. 

 H2S/L) (4) there remained doubt whether an enrichment of sul- 

 phate-reducing thermophiles had been obtained. There seems 

 to be no reason in principle why marine thermophiles should 

 not in fact exist; the authors have "trained" a type strain of CI. 

 nigrificans (Starkey's strain 74T; NCIB 8395) to grow in media 

 containing 2.5% NaCl. The training process was relatively diffi- 

 cult, involving the sequential subcultures recorded in Table 1, 

 but the adapted strain grew well in saline media and was mor- 

 phologically noiTnal. Filamentous growth restricted to the preci- 

 pitate occurred during the training ( in this respect the behaviour 

 of the organism recalled that of fresh-water D. desulfuricans to 

 be described later). D. orientis has only recently been defined 

 as a species, and though it is more ubiquitous than was at first 

 thought (1), the few marine samples that have been examined 

 for this species (three to the authors' knowledge) have not shown 

 it. In this case there is even less reason why marine types sliould 

 not exist; the holotype strain of D. orientis (Singapore; NCIB 

 8382), though obtained from a fresh water environment, grows 



