Carbon monoxide oxidation by bacteria associated with the roots of freshwater macrophytes

The potential rates and control of aerobic root-associated carbon monoxide (CO) consumption were assessed by using excised plant roots from five commo n freshwater macrophytes. Kinetic analyses indicated that the maximum poten tial uptake velocities for CO consumption ranged from 0.4 to 2.7 mu mol of CO g (dry weight)(-1) h(-1) for the five species. The observed rates were c omparable to previously reported rates of root-associated methane uptake. T he apparent half-saturation constants for CO consumption ranged from 50 to 370 nM CO; these values are considerably lower than the values obtained for methane uptake. The CO consumption rates reached maximum values at tempera tures between 27 and 32 degrees C, and there was a transition to CO product ion at greater than or equal to 44 degrees C, most likely as a result of th ermochemical organic matter decomposition. Incubation of roots with organic substrates (e.g., 5 mM syringic acid, glucose, alanine, and acetate) drama tically reduced the rate of CO consumption, perhaps reflecting a shift in m etabolism by facultative CO oxidizers. Based on responses to a suite of ant ibiotics, most of the CO consumption (about 90%) was due to eubacteria rath er than fungi or other eucaryotes, Based on the results of acetylene inhibi tion experiments, methanotrophs and ammonia oxidizers were not active CO co nsumers.