THREE DECADES PROGRESS IN MICROBIOLOGY 



A survey of thirty years progress in microbiological metabolism would 

 be very incomplete, if not due attention was given to the enormous 

 amount of very successful work which has been performed on the sub- 

 ject of growth factors, leading to the discovery of the rather common 

 occurrence amongst micro-organisms of a phenomenon that later has 

 been termed auxo-heterotrophy by Schopfer. As is well-known the 

 first observations regarding this phenomenon date back to 1900 when 

 Wildiers demonstrated that a certain strain of yeast would only prolif- 

 erate in a medium containing sugar and the necessary quantities of in- 

 organic nutrilites, if a small quantity of yeast extract or some other 

 vegetable extract was added to the medium. For the growth-promo- 

 ting principle present in these extracts Wildiers coined the term bios. 

 The development in this field is too generally known to be in need of 

 further documentation, yet it seems worth while to devote a few re- 

 marks to the general aspects which have resulted from these studies. 



In the first place it has been definitely proved that the various 

 growth factors which have appeared to be essential - often in surpris- 

 ingly small quantities - for the development of certain micro-organ- 

 isms are nearly all known to act also as accessory food factors in animal 

 metabolism. Wildiers' bios has been shown to be composed of various 

 factors which could be identified as biotin, thiamine, pyridoxine, in- 

 ositol, pantothenic acid, nicotinic acid and p.aminobenzoic acid, and 

 for all these compounds it has now definitely been established that 

 they are indispensable food constituents for special types of test ani- 

 mals, on the understanding that their absence in the food either in- 

 hibits growth or leads to certain other defects. 



A second important viewpoint is that already much light has been 

 thrown on the way in which these mysterious growth factors exert their 

 beneficial action on the cell, apparently many of them, if not all, are 

 essential components of certain enzyme systems. So for instance thi- 

 amine has been found to be the active group of the cocarboxylase, 

 the enzyme which decarboxylates pyruvic acid, nicotinic acid is the 

 active group of the dehydrogenase-system, riboflavin is part of one of 

 the respiratory enzymes, and recently it has been proved that a pyri- 

 doxine derivative is the active principle in the decarboxylation of 

 amino acids. 



An at first sight disturbing factor is that a phylogenetic study of the 

 distribution of the property of auxo-heterotrophy has learnt that on 



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