Fig 6. High intracellular Mn triggers a toxic dysfunction of QoxABCD.

A schematic depiction of cellular responses to high Mn for cells growing in MM-malate (green arrow and shading) or MM-glucose (pink arrow and shading). Intracellular Mn (silver circles) is regulated by both import (MntH and MntABC, left) and efflux (MneP and MneS, upper left and lower right). In the absence of efflux (PS mutant), RRS accumulate, as detected by reaction with DCF. On MM-glucose, loss of pyruvate kinase (Pyk) or a Mg efflux pump (MpfA) is beneficial. On MM-malate, Mn toxicity is suppressed by loss of QoxA (qoxA::mTn), derepression of the MhqR regulon, a mutation of ctaA that converts QoxABCD into a bo₃-type oxidase, or expression of CydABCD bd-type oxidases (rex mutation or ectopic induction).