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A Biotin-Regulated Locus, bioS, in a Possible Survival Operon of Rhizobium meliloti

A novel biotin-inducible DNA locus, bioS, was found in Rhizobium meliloti 1021 by mutation with a transposable promoter probe. The promoterless nptII reporter responded to 40 nM biotin with a sixfold increase in NPTII protein. Stationary-phase mutant cells accumulated 50% more ¹⁴C-biotin than corresponding wild-type cells. The prototrophic mutant competed equally with the wild type in biotin-free medium but poorly when 40 nM biotin was present. The 588-bp bioS is located among three genes showing homology to survival operons of other bacteria, and it may be part of a system that R. meliloti uses to respond to plant biotin signals.