NUTRITION OF MICRO-ORGANISMS 



Attempts to use C. ulmi for assaying pyridoxine were unsuccessful, 

 however, the growth-response curves being too irregular.^ Both aneur- 

 ine and pyridoxine were essential growth factors for the closely-related 

 micro-organisms, C multiannulata, C. fagi, C. piliferum, C. plurian- 

 nulatum and Ascoidea ruhescens,''* ^ and for Ophiostoma catonianum.^ 



Another mould that required pyridoxine was a mutant of Neuro- 

 spora sitophila, produced by irradiating the normal strain with X-rays. ^^ 

 It is generally referred to as the pyridoxineless mutant as it will not 

 grow on a medium containing ammonium tartrate as the source of 

 of nitrogen unless pyridoxine is added. Growth does occur, however, 

 when other sources of nitrogen are used. Also, pyridoxine can largely 

 be replaced by aneurine, so that when this organism is used for the 

 estimation of pyridoxine (see page 313) care must be taken to eliminate 

 aneurine from the test solutions. 



Another mould that responded to pyridoxine was Penicillium 

 digitatum}'^ P. chrysogenum, however, synthesised pjnridoxine, twice 

 as much being present in the culture fluid as in the basal medium. ^2 



Bacteria 



Incidental reference has already been made (page 312) to several 

 bacteria for which pyridoxine is an essential growth factor ; some of 

 these have been used in assaying pyridoxine and its derivatives. 

 M. Landy and D. M. Dicken ^^ suggested Lactobacillus helveticus as a 

 test organism for the assay of pyridoxine, but it proved to be less 

 satisfactory for this purpose than the pyridoxineless mutant of N. 

 sitophila. It was found that the addition of DL-alanine to the medium 

 of Landy and Dicken greatly increased the response of L. helveticus 

 to pjnridoxine,^* and that the organism could grow without pyridoxine 

 if DL-alanine and an enzymic hydrolysate of vitamin-free casein were 

 added to the medium. ^^ Similarly, 5. faecalis R could grow without 

 pyridoxine when DL-alanine was added. In both instances the effect 

 of DL-alanine was due to the D-isomer, but in the presence of pyri- 

 doxine, the L-isomer also had a growth-promoting effect, which was 

 actually greater than that of D-alanine. This phenomenon has not yet 

 received an adequate explanation, but it seems unlikely that alanine 

 is a precursor of pyridoxine, as suggested by E. E. Snell and B. M. 

 Guirard,^^ since a possible intermediaite, a-formiminopropionic acid : 



00 C 



HO.C HO-C O HO-C C.CH2OH 



I — I II — > I II 



CH3.CH CH3.C CH CH3.C CH 



\ \ / \/ 



NH2. N N 



339 



