Requirement for Riboflavin for Effective Symbiosis on Clover by an Auxotrophic Mutant Strain of Rhizobium Trifolii

A symbiotically ineffective auxotroph, Tl/D-hisr -15, derived from an effective strain (Tl) of R. trifolii, had a specific requirement for riboflavin in culture and produced an effective response on Trifolium pratense (red clover) only when riboflavin was added to the plant growth medium at c. 6 p.g/ml. Addition of flavin mononucleotide to the plant medium produced a similar response but the requirement in symbiosis was only partly satisfied by flavin adenine dinucleotide.