SIOGRAPIIICAL MEMORANDA 



members of the group of aerobic sporeforming bacteria; this applies, 

 for instance, to the species, Schizosaccharomyces hominis, [Dorrepaal, 

 1930], and to the genus, Schizotorulopsis [Verkaik, 193 1]. 



Besides these contributions should be noted the monographs dealing 

 with the yeast genus, Brettanomyces [Custers, 1940Tb], and with the 

 species, Candida pulcherrima [van der Walt, 1952Tb]. The latter con- 

 tains the fascinating observations on the pigments produced by this 

 yeast in the presence of various heavy metals. This study eventually 

 led Kluyver and co-workers [1953] to the isolation and characteri- 

 zation of pulcherrimin, surely one of the most interesting chelating 

 agents known to-day. 



VARIABILITY OF MICRO-ORGANISMS 



From the preceding section it will be clear that Kluyver knew micro- 

 organisms as more than entities performing special biochemical trans- 

 formations, which implies that he was also familiar with that bane of 

 the systematist that can conveniently be described by the collective 

 term, 'variability'. 



Variability expresses itself in physiological as well as morphological 

 respects. Both of these have been studied in Kluyver's institute, and 

 some of the contributions to this aspect of microbial behaviour will 

 here be briefly reviewed. 



In 1925 Elion [1925] had there discovered a bacterial sulphate re- 

 duction at temperatures as high as 65°C; the causative agent had been 

 isolated and described as Vibrio thermode sulfuric ans ; it was the third spe- 

 cies of sulphate-reducing bacteria, the previously known ones being the 

 mesophilic freshwater V. desulfuricans and the marine V. aestuarii. The 

 isolation of V. thermo desulfuricans, unable to grow at temperatures be- 

 low 30°C, presented a curious problem, however. The cultures had 

 been started with an inoculum of mud taken from a ditch below a 

 heavy layer of ice, and it seemed most improbable that even during 

 warm seasons the temperature of the mud in this ditch would ever 

 reach the minimum temperature required for growth of the new 

 species. This raised the question how its apparently regular occurrence 

 in this environment could be explained. 



Some years later this situation led Kluyver and Baars to the idea 

 that V. thermodesulfuricans might not be an autonomous species, but 



146 



