Improved H +/O ratio and cell yield of Escherichia coli with genetically altered terminal quinol oxidases

Abstract

Escherichia coli wild-type cells, containing both cytochrome bo- and bd-type terminal oxidases, pumped protons with a H +/O ratio of 4.5–4.9 upon an oxygen pulse, while mutant cells, deprived of either cytochrome bo (Δ cyo) or bd (Δ cyd), showed values of 3.5–4.1 or 4.8–5.6, respectively. The cell yield of the cyo-less mutant was about 15% lower than that of the wild-type strain, while that of the cyd-less strain which over-produced cytochrome bo was about 10% higher than that of the wild-type. The simple cyd-less strain without over-production of cytochrome bo showed a high H +/O ratio, but its cell yield was low and variable from culture to culture. The growth inhibition and accelerated H + permeability of the cell membrane of the latter strain seems due to the deletion of cytochrome bd (CydAB), the terminal oxidase having a very low K m for O 2, which may result in severe stress on the cell. Over-production of cytochrome bo by as much as 0.4 nmol/mg membrane protein could compensate for this defect.