Effect of CO and light on ammonium and nitrite oxidation by chemolithotrophic bacteria

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Abstract
The effects of CO and light on the ammonium oxidizing bacterium Nitrosomonas cryotolerans and the nitrite oxidizing bacterium Nitrobacter sp. Nb297 were investigated. Ammonium oxidation was inhibited by CO concentrations ranging from 2 nM to 11.4 .mu.M. CO inhibition was cell density dependent and increased if the cells had been either previously starved or deprived of iron. Ammonium oxidation was inhibited by 63% at intensities as low as 5 W m-2 of artificial light. Nitrobacter sp. Nb297, on the other hand, was able to tolerate CO concentrations as high as 400 .mu.M. Artificial lights (25 W m-2) slightly reduced nitrite oxidation while sunlight (628 W m-2) decreased activity to ca 20% of its original value. In addition, CO and CH4 oxidation by N. cryotolerans and natural assemblages of bacteria were inhibited by light. It is apparent from these studies that the mechanisms of light and CO inhibition are different for the NH4+ and NO2-oxidizers examined. Characterization of light and CO responses by marine nitrifying bacteria is critical in any attempt to explain the formation of the subsurface primary nitrite maximum.