Hydrogen production in the presence of oxygen by K-12.

is a facultative anaerobe that can grow in a variety of environmental conditions. In the complete absence of O, can perform a mixed-acid fermentation that contains within it an elaborate metabolism of formic acid. In this study, we use cavity-enhanced Raman spectroscopy (CERS), FTIR, liquid Raman spectroscopy, isotopic labelling and molecular genetics to make advances in the understanding of bacterial formate and H metabolism. It is shown that, under anaerobic (anoxic) conditions, formic acid is generated endogenously, excreted briefly from the cell, and then taken up again to be disproportionated to H and CO by formate hydrogenlyase (FHL-1). However, exogenously added D-labelled formate behaves quite differently from the endogenous formate and is taken up immediately, independently, and possibly by a different mechanism, by the cell and converted to H and CO. Our data support an anion-proton symport model for formic acid transport. In addition, when was grown in a micro-aerobic (micro-oxic) environment it was possible to analyse aspects of formate and O respiration occurring alongside anaerobic metabolism. While cells growing under micro-aerobic conditions generated endogenous formic acid, no H was produced. However, addition of exogenous formate at the outset of cell growth did induce FHL-1 biosynthesis and resulted in formate-dependent H production in the presence of O.