Non-enzymic copper reduction by menaquinone enhances copper toxicity in Lactococcus lactis IL1403
Abicht, Helge K. and Gonskikh, Yulia and Gerber, Simon D. and Solioz, Marc,, 159, 1190-1197 (2013),
doi = https://doi.org/10.1099/mic.0.066928-0,
publicationName = Microbiology Society,
issn = 1350-0872,
abstract= Lactococcus lactis possesses a pronounced extracellular Cu2+-reduction activity which leads to the accumulation of Cu+ in the medium. The kinetics of this reaction were not saturable by increasing copper concentrations, suggesting a non-enzymic reaction. A copper-reductase-deficient mutant, isolated by random transposon mutagenesis, had an insertion in the menE gene, which encodes O-succinylbenzoic acid CoA ligase. This is a key enzyme in menaquinone biosynthesis. The ΔmenE mutant was deficient in short-chain menaquinones, and exogenously added menaquinone complemented the copper-reductase-deficient phenotype. Haem-induced respiration of wild-type L. lactis efficiently suppressed copper reduction, presumably by competition by the bd-type quinol oxidase for menaquinone. As expected, the ΔmenE mutant was respiration-deficient, but could be made respiration-proficient by supplementation with menaquinone. Growth of wild-type cells was more copper-sensitive than that of the ΔmenE mutant, due to the production of Cu+ ions by the wild-type. This growth inhibition of the wild-type was strongly attenuated if Cu+ was scavenged with the Cu(I) chelator bicinchoninic acid. These findings support a model whereby copper is non-enzymically reduced at the membrane by menaquinones. Respiration effectively competes for reduced quinones, which suppresses copper reduction. These findings highlight novel links between copper reduction, respiration and Cu+ toxicity in L. lactis.,
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