450 Marine Microbiology 



concentration, require some nucleotides (AMP, ATP, APS, etc) 

 and amino acids (all or some of the following: arginine, lysine, 

 phenylalanine, serine, threonine, leucine, isoleucine, valine, glu- 

 tamic acid, aspartic acid, alanine, cystine, glycine, histidine, 

 methionine, proline, tryptophane, and tyrosine) for the normal 

 or nearly normal growth. These substances seem to be required 

 by these organisms as growth-stimulating factors rather than 

 essential growth factors in the strict sense of the word. 



The high activity of nucleotides as growth-stimulating factors 

 in the present case may principally be due to the extraordinarily 

 great need for ATP by these microorganisms in the energy-yield- 

 ing reactions indispensable for the multiplication of the cells; it 

 was recently found by Peck (15) and Ishimoto (8, 9) that ATP 

 participated in the energy-yielding reaction which was linked to 

 the reduction of sulfate to sulfide ion through the following path- 

 ways when sulfate was present: 



S02-4 + ATP = APS + PP 

 APS + H. = S02-3 + AMP 

 S02-3 + 3H2 = S2- + 3H.O 



Accordingly, the amount of ATP required for the growth (es- 

 pecially, for the initiation of growth) by these microorganisms 

 is expected to be considerably larger than that in the cases of 

 usual microorganisms; the amounts of AMP, ATP and APS in- 

 itially present in the inoculum of ordinary size are thought to be 

 too small for supporting the normal multiplication of the cells 

 of these microorganisms. Although purines and nucleosides appear 

 to be hardly available for the synthesis of ATP or APS in the 

 cells, AMP and adenosine-3'-monophosphate seem to be relatively 

 easily transformed by the cells to APS via ATP in the presence of 

 sulfate, and subsequently be used for the sulfate reduction. 



The previously reported facts that these bacteria were able 

 to be grown in the media without any natural substance of in- 

 definite composition only (1) when an inoculum of abnormally 

 large size was employed; (2) or when certain other microorgan- 

 isms coexisted in the culture, may reasonably be explained by the 

 above described findings. 



