UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



colloidal sulphur in the form of droplets and as a reserve material in 

 their cells, and which had long been known to naturalists, there exists 

 another large group of small bacteria that, though producing sulphur 

 extra-cellularly when grown in sulphide media, yet must be reckoned 

 as belonging to the physiological group of sulphur bacteria on account 

 of their metabolic behaviour which is similar to that of Beggiatoa. 

 These bacteria, discovered by Nathansohn, but studied more particul- 

 arly by Beijerinck, Lieske [1912], and Jacobsen [1912, 1914], have 

 recently been much discussed in America, and permit me to give you 

 another striking example of the chemical proficiency of the microbes. 

 In a series of papers the American microbiologist, Waksman [1922], 

 has reported on the astounding properties of an organism, designated 

 as Thiobacillus thiooxidans, that can also oxidize sulphur powder to sul- 

 phuric acid, and get along with carbon dioxide as the sole carbon source. 

 It differs from Thiobacillus thioparus, earlier described by Beijerinck and 

 by Jacobsen, especially by its insensitivity to acid which is so pro- 

 nounced that in certain media the pH reaches 0.6. Nay, J. G. Lipman, 

 the well-known editor-in-chief of 'Soil Science', has communicated 

 in a recent paper that T. thiooxidans can still effect a perceptible sul- 

 phur oxidation in solutions containing 5 per cent sulphuric acid. 



It should not surprise you that this powerful ability to produce 

 sulphuric acid has been exploited in different directions in the U.S.A. 

 I shall mention but one example because, in a sense, it implies an 

 attack on one of the branches of chemical industry. Lipman and 

 Waksman have already carried out experiments on a rather extensive 

 scale to test the possibility of circumventing the commercial manufac- 

 ture of superphosphate by fertilizing the soil with a mixture of natural 

 phosphate and free sulphur, and thus causing the localized formation 

 of sulphuric acid, hence also of superphosphate, through the activity 

 of T. thiooxidans. In certain soils this treatment appears to have given 

 fully satisfactory results. 



As far as an impressive chemical performance is concerned the last- 

 mentioned bacterium is still exceeded, however, by Beijerinck's T. 

 denitrificans which can grow in the complete absence of oxygen and 

 gaseous carbon dioxide in a medium containing sulphur, potassium 

 nitrate, chalk, and a small amount of phosphate ; thus it should be 

 able to produce organic matter from these compounds in deeper soil 

 layers. 



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