KLUYVER S CONTRIBUTIONS TO MICROBIOLOGY AND BIOCHEMISTRY 



rather a modified form of the mesophilic V. desulfuricans. By using 

 large inocula of a pure culture of the latter, and incubating transfers 

 at increasingly elevated temperatures, it proved indeed possible to 

 effect a change in the properties of the organism which appeared to 

 involve a gradual shift in the entire temperature range within which 

 the strain could develop. In like manner the reverse was also accom- 

 plished, and a thermophilic culture changed into a mesophilic one. 



These experimentally induced modifications strongly supported the 

 view that V. desulfuricans and V. thermo desulfuricans represented more 

 or less stabilized races of one and the same organism rather than dis- 

 tinct and separate species. This further led to experiments designed to 

 determine whether V. desulfuricans and V. aestuarii might be similarly 

 related. Hitherto these species had been distinguished solely because 

 the former can develop normally in media with 0-1.5 P er cent sodium 

 chloride, but is inhibited by higher concentrations, and unable to 

 grow with more than 2.5 per cent, whereas the latter grows equally 

 rapidly in media with 1-3 per cent, and not at all with less than 0.5 

 per cent salt. By transferring cultures to media with different salt 

 content it was found that the range of salt concentrations at which un- 

 inhibited growth can occur is just as little fixed as is the temperature 

 range, and that these two types can also be gradually interconverted. 

 Consequently it was proposed to recognize only V. desulfuricans as a 

 taxonomically sound species; the others were graphically designated 

 as 'physiological artefacts' [Kluyver and Baars, 1932; Baars, 1930Tb]. 



The thermophilic nature of Elion's isolate could be more easily 

 understood when Starkey [1938], working in Kluyver's laboratory, dis- 

 covered that sulphate reduction at elevated temperatures is caused by a 

 sporeforming bacterium. At the time this was considered to be ident- 

 ical with the 'adapted' mesophilic cultures of Baars, and designated 

 as Sporovibrio. But recent studies have shown that the experimental 

 results of Kluyver and Baars are not reproducible. Eventually this 

 situation has led Campbell et al [1957] to identify Starkey's Sporovibrio 

 as Clostridium nigrificans, a sporeforming anaerobe that had long been 

 known as the causative agent of hydrogen sulphide production in cer- 

 tain canned products. This conclusion has lately been corroborated in 

 Kluyver's laboratory as well as by Starkey. It therefore seems probable 

 that the earlier results must be attributed to the use of impure cultures. 



Interconversion of freshwater and marine strains of Desulfovibrio 



147 



