ISSN:
1572-8773
Keywords:
Bradyrhizobium japonicum
;
divalent cations
;
hydrogenase
;
metal accumulation
;
metal transport
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Hydrogenase-constitutive (Hupc) mutants of Bradyrhizobium japonicum were previously shown to accumulate more nickel than the wild-type strain. In a 2 h period Hupc strains JH101 and JH103 also accumulated 2- to 3-fold more Mg2+, Zn2+ and Cu2+, and about 4-fold more Co2+ and Mn2+ than the wild-type strain JH. Init uptake rates (first 10 min) by the Hupc strains were also greater for all the metals. The mutation in the Hupc strains affecting a trans-acting regulator of the hup structural genes appears to have also amplified a metal uptake/accumulation process common to many divalent metal ions. From efflux experiments (suspension of cells in metal-free medium after metal accumulation) to determine the degree of dissociation of each metal with the cells it was concluded that Zn2+, like Ni2+, was rapidly and tightly cell-associated. In contrast, about 50% of the accumulated Cu2+ and about 30% of the Mn2+ was effluxed within 2 h by both the Hupc and wild-type strains. Cobalt was more tightly cell-associated than Mn2+ or Cu2+, as the strains effluxed about 26% of the previously accumulated metal in 2 h. Even after accounting for ‘effluxed metal’, the Hupc strains retained more of each metal than the wild-type. The increased metal accumulation by Hupc strains could not be accounted for solely at the level of transport, as known metabolic inhibitors (carbonyl cyanide m-chlorophenylhydrazone and nigericin) of nickel transport partially inhibited (1 h) accumulation of only some (magnesium, zinc and copper) of the other metals. Hydrogenase-derepressed wild-type cells exhibited slightly higher (22–27% more) 2 h accumulation capacity for some of the metals (nickel, zinc and copper) than did non-derepressed cells, but not to the 2- to 4-fold greater level observed for Hupc strains compared with the wild-type. The Hupc strains JH101 and JH103 do not synthesize more capsular/cell wall carbohydrate than the wild-type strain.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00144122
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