Introduction

Abstract

Carbon monoxide (CO) is an atmospheric trace gas. Its concentration in the Earth’s atmosphere ranged between 0.06 and 0.15 ppm (IPCC in Climate Change 2001; the scientific basis; Cambridge University Press, New York, 2001). CO is a potent electron donor (E^o′−524 to 558 mV for the CO/CO₂ couple) (Grahame and DeMoll in Biochemistry 34:4617–4624, 1995), and although it may be inhibitory to iron proteins of both aerobes and anaerobes (Adam in Biochim Biophys Acta 1020:115–145, 1990), CO is utilized by many microorganisms. CO-oxidizing microorganisms or simply carboxydotrophs are taxonomically diverse group of microorganisms and represent a type of chemolithoautotrophic metabolism capable of catalyzing the oxidation of CO to CO₂. The term carboxydotrophs was originally coined for microbes with aerobic, respiratory, chemolithoautotrophic utilization of CO as a sole source of carbon and energy (Meyer and Schlegel in Annu Rev Microbiol 37:277–310, 1983).