Role of carboxydobacteria in consumption of atmospheric carbon monoxide by soil.

The carbon monoxide consumption rates of the carboxydobacteria Pseudomonas (Seliberia) carboxydohydrogena, P. carboxydovorans, and P. carboxydoflava were measured at high (50%) and low (0.5 mul liter) mixing ratios of CO in air. CO was only consumed when the bacteria had been grown under CO-autotrophic conditions. As an exception, P. carboxydoflava consumed CO also after heterotrophic growth on pyruvate. At low cell densities the CO consumption rates measured at low CO mixing ratios were similar in cell suspensions and in mixtures of bacteria in soil. CO consumption observed in natural soil (loess, eolian sand, chernozem) as well as in suspensions or soil mixtures of carboxydobacteria showed Michaelis-Menten kinetics. The K(m) values for CO of the carboxydobacteria (K(m) = 465 to 1,110 mul of CO liter) were much higher than those of the natural soils (K(m) = 5 to 8 mul of CO liter). Considering the difference of the K(m) values and the observed V(max) values, carboxydobacteria cannot contribute significantly to the consumption of atmospheric CO.