136 



obtaining of pure cultures, as will easily be understood by those bac- 

 teriologists who have worked with strictly anaerobic, non-spore- 

 forming bacteria i). However, finally Beijerinck was successful. 



A careful pure-culture study of the exceptional metabolic activities 

 of Vibrio desulfuricans was only performed eight years later in colla- 

 boration with van Delden 2). This investigator was also able to 

 prove that the sulphate reduction which takes place so profusely in 

 brackish water at various spots along the Dutch coast is caused by a 

 bacterium which has again a spirillum or comma shape and which 

 apparently is very closely related to Vibrio desulfuricans. 



It is noteworthy that from time to time publications appear in 

 which authors claim that organisms which are evidently widely differ- 

 ent from Vibrio desulfuricans also possess the ability to reduce sul- 

 phates. Baars' monograph on the subject makes it clear that these 

 claims have never been substantiated ^) . In this connection it is also 

 most significant that the study made by Elion 4) on sulphate reduct- 

 ion under thermophilic conditions led to the conclusion that here too 

 the reduction proceeded under the influence of a vibrio-shaped bac- 

 terium, closely related to Vibrio desulfuricans. The mass of evidence 

 now available is, therefore, in favour of the view that biological 

 sulphate reduction, the practical importance of which is becoming 

 more manifest every day 5) , is exclusively due to the activity of one of 

 the varieties of a bacterium which was for the first time observed, 

 isolated, and described by Beijerinck. 



m. 071 denitrification. 



As has been observed in the preceding section, Beijerinck's con- 

 tributions to our knowledge of the process of nitrate reduction do 

 not have the same fundamental character as his studies devoted to the 

 process of sulphate reduction. This does not diminish the value of 

 some very remarkable observations made by him upon special featu- 

 res of the denitrification process. 



It is greatly to the credit of the French investigators Gayon and 

 Dupetit to have shown, so early as 1886, that the reduction of nitra- 

 tes under the influence of a special bacterium led to the formation of 

 nitrous oxide as well as of f ree nitrogen. This observation had not 

 given rise to any further work till Beijerinck took up the question 



1) Only recently Starkey, working in the Delft microbiological laboratory, has 

 made the startling observation that under certain conditions Vibrio desulfuricans is 

 able to form true endospores. Cf. R. L. Starkey, Archiv f. Mikrobiol. 9, 26^, 1938. 



2) Arch. d. Sciences exactes et naturelles Sér. II, 9, 131, 1904. A more detailed 

 publication of van Delden had appeared a year before. Cf. A. H. van Delden, Central- 

 bl. f. Bakt. u. Parasitenk. II, 11, 81 und 113, 1903. 



3) J. K. Baars, Over sulfaatreductie door bacteriën. Delft, 1930. 

 ") L. Elion, Centralbl. f. Bakt. u. Parasitenk. II, 63, 58, 1924. 



5) Cf. C. A. H. VON WoLZOGEN KÜHR and L. S. van der V^lugt, The graphitiza- 

 tibn of cast iron as an electro-biochemical process in soils. The Hague, 1934. 



