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J. Bacteriol., Jan 1997, 209-216, Vol 179, No. 1
A Ichige and GC Walker
The Rhizobium meliloti bacA gene encodes a function that is essential for
bacterial differentiation into bacteroids within plant cells in the
symbiosis between R. meliloti and alfalfa. An Escherichia coli homolog of
BacA, SbmA, is implicated in the uptake of microcin B17, microcin J25
(formerly microcin 25), and bleomycin. When expressed in E. coli with the
lacZ promoter, the R. meliloti bacA gene was found to suppress all the
known defects of E. coli sbmA mutants, namely, increased resistance to
microcin B17, microcin J25, and bleomycin, demonstrating the functional
similarity between the two proteins. The R. meliloti bacA386::Tn(pho)A
mutant, as well as a newly constructed bacA deletion mutant, was found to
show increased resistance to bleomycin. However, it also showed increased
resistance to certain aminoglycosides and increased sensitivity to ethanol
and detergents, suggesting that the loss of bacA function causes some
defect in membrane integrity. The E. coli sbmA gene suppressed all these
bacA mutant phenotypes as well as the Fix- phenotype when placed under
control of the bacA promoter. Taken together, these results strongly
suggest that the BacA and SbmA proteins are functionally similar and thus
provide support for our previous hypothesis that BacA may be required for
uptake of some compound that plays an important role in bacteroid
development. However, the additional phenotypes of bacA mutants identified
in this study suggest the alternative possibility that BacA may be needed
for membrane integrity, which is likely to be critically important during
the early stages of bacterial differentiation within plant cells.
Copyright © 1997, American Society for Microbiology
Genetic analysis of the Rhizobium meliloti bacA gene: functional interchangeability with the Escherichia coli sbmA gene and phenotypes of mutants
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
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