Escherichia coli Uses a Dedicated Importer and Desulfidase To Ferment Cysteine
Yidan Zhou, James A. Imlay
Abstract
operon of Escherichia coli serves to detoxify cysteine by degrading it. The present study indicates, however, that the natural purpose of that operon is to provide a concise route of cysteine fermentation. CyuP is the first dedicated cysteine importer to be functionally validated among the bacteria, and CyuA constitutes a cysteine desulfidase. Intriguingly, the CyuA iron-sulfur cofactor is inactivated by oxygen so that cysteine is, uniquely, a carbon source that is usable only in anoxic environments. Presumably, this constraint is tolerable because cysteine is scarce in oxic habitats. It also avoids sulfide release, which could interfere with aerobic respiration. Cysteine joins just serine and threonine as amino acids that E. coli is known to ferment, underscoring that this facultative bacterium is oriented toward the fermentation of carbohydrates.