Effect of genomic rearrangement on heavy metal tolerance in the plant-growth-promoting rhizobacterium <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp245 |
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Authors: | Andrei V Shelud’ko Olga E Varshalomidze Lilia P Petrova Elena I Katsy |
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Institution: | (1) Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, 13 Prospekt Entuziastov, 410049 Saratov, Russia; |
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Abstract: | A derivative of Azospirillum brasilense Sp245, Sp245.5, which spontaneously lost 85 and 120 MDa replicons upon the formation of a new megaplasmid, has been shown
to produce a novel lipopolysaccharide and to lose Calcofluor-binding polysaccharides. As compared to Sp245, the derivative
displays notably increased heavy metal tolerance. The phenotypes of Sp245 and Sp245.5 are characterized by the following minimal
inhibitory concentrations (MICs) of heavy metals: 0.5 and 0.9 μmol l−1 of Ag+, 0.4 and 0.7 mmol l−1 of Co2+, 0.9 and 4.7 mmol l−1 of Cu2+, and 3.1 and 11.5 mmol l−1 of Zn2+, respectively. In Sp245, in the presence of a nonlethal concentration (0.625 μmol l−1) of the efflux pump inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP), the MIC of cobalt, copper, and zinc drop 1.3- to 1.6-fold, but the low tolerance to silver
is unaffected. In Sp245.5, CCCP does not affect cobalt tolerance, suppresses tolerance to copper and silver to the wild-type
levels, and causes a 1.4-fold decrease in resistance to zinc. Therefore, significant elevation of heavy metal tolerance in
Sp245.5 seems caused by the induction/overexpression of the proton-dependent efflux of certain metal ions. The novel cell
surface and other unknown factors could also be responsible for the increased tolerance of A. brasilense Sp245.5 to heavy metals. |
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