A homologue of
Sinorhizobium meliloti bacA was isolated from Mesorhizobium huakuii 7653R, which is capable of fixing atmospheric
nitrogen in symbiotic association with leguminous
Astragalus sinicus (Chinese
milk vetch). Inactivation of the bacA gene abolished the ability of M. huakuii 7653R to establish a successful symbiosis with its host plant. Simultaneously, compared with
wild-type M. huakuii 7653R, the bacA
mutant was more sensitive to cell envelope-disrupting agents (acidic
solution,
ethanol, SDS, and
crystal violet).
Mass spectrometry analysis revealed that the very-long-chain
fatty acid (27-OHC-28:0 and 29-OHC-30:0) contents of
lipid A was reduced in the M. huakuii 7653R bacA
mutant. Taken together, our data suggest that the
cell envelope was altered in the M. huakuii 7653R bacA
mutant, which might deteriorate
bacterial adaption to acute
environmental changes encountered in
host cells and ultimately result in the failure of Mesorhizobium-legume symbiosis.
