Qualitative Studies of Soil Microorganisms: Xiv. Specific Vitamin Requirements of the Predominant Bacterial Flora

A relatively high proportion of the indigenous bacteria of a field soil (27.1%, corresponding to 14.1 millions/g.) required one or more vitamins for growth. The vitamins found to be essential, either alone or with others, were, in order of frequency, thiamine, biotin, vitamin B 12 , pantothenic acid, folic acid, nicotinic acid, and riboflavin. In all, 16 different 'patterns' were noted for vitamin requirements, the number of vitamins needed by individual strains ranging from one to five. The findings point to the soil as an important habitat of vitamin-requiring bacteria, many of which show potentiality as assay organisms. Their occurrence in the numbers found indicates that growth-factors should receive equal emphasis with antibiotics in problems involving the microbial equilibrium in soil and interrelationships between the normal soil microflora, soil-borne disease organisms, and growing plants.