Metabolism of acetylene and acetaldehyde by Rhodococcus rhodochrous

We studied the ability of a soil bacterium, identified as Rhodococcus rhodochrous, to grow on acetylene and to accumulate acetaldehyde. Its maximum growth rate on acetylene was obtained at about 30 degrees C (mu = 0.11 h-1) and was independent of the concentration of this gas in air from 0.14 to 16% (v/v). During growth, acetylene was quantitatively transformed to acetaldehyde, ethanol, acetate, CO2, and biomass in proportions which varied with culture age and temperature. Growth was completely inhibited by acetaldehyde at a concentration of 10 mM. The inhibitory effect was relieved by addition of acetate. Growth on ethanol up to 140 mM did not result in acetaldehyde accumulation. Acetylene consumption was constitutive with apparent Km and Vmax equal to 250 microM and 800 nmol.min-1.(mg protein)-1, respectively. In resting cell suspensions, acetylene consumption rates decreased more rapidly under air than under nitrogen. The inhibitory effect of acetaldehyde was enhanced in the presence of oxygen. Acetaldehyde accumulation in aerobic resting cell conditions did not exceed 10 mM (440 mg/L), but under anaerobic conditions it attained more than 70 mM (3.08 g/L).