Role of Carboxydobacteria in Consumption of Atmospheric Carbon Monoxide by Soil

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Abstract
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 μl liter−1) 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 Km values for CO of the carboxydobacteria (Km = 465 to 1,110 μl of CO liter−1) were much higher than those of the natural soils (Km = 5 to 8 μl of CO liter−1). Considering the difference of the Km values and the observed Vmax values, carboxydobacteria cannot contribute significantly to the consumption of atmospheric CO.