Several yeast water preparations and commercial yeast extracts varied in their toxicity to two strains of Rhizobium trifolii. Strains of R. japonicum and R. leguminosarum were also susceptible to yeast extract, while strains of R. meliloti were resistant.
An interaction between glycine and monovalent cations was the main cause of yeast extract toxicity. Divalent cations, notably Ca2+, added to inhibitory media prevented the toxicity and enhanced growth with increased concentrations of yeast extract.
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