Carbon monoxide production is not enhanced by nitrogenase activity

fA diverse group of nitrogen-fixing bacteria and two heme degraders were gr own with and without fixed nitrogen sources under oxic and suboxic conditio ns, with and without addition of heme-containing compounds. Several of the strains produced carbon monoxide (CO) under one or more of these conditions , but nitrogenase activity did not stimulate rates of production relative t o controls. Although nitrogenase can reduce CO2 to CO in vitro in the absen ce of N-2, this process likely contributes minimally to CO production in so ils under in situ conditions. In contrast, myoglobin or hematin addition un der oxic conditions significantly stimulated CO production by the heme degr aders. However, estimates of CO production from microbial heme turnover sug gest that this too is likely to be only a small source of CO in soils in si tu. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.