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

The effects of CO and light on the ammonium oxidizing bacterium Nitrosomonas cryotolerans and the nitrite oxidizing bacterium N~trobacter sp Nb297 were investigated. Ammonium oxldahon was inhibited by C O concentrations ranging from 2 n M to 11.4 FM. 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 a s low a s 5 W m-2 of artificial light. Nitrobactersp. Nb297, on the other hand, was able to tolerate C O concentrations as high as 400 PM. Artificial light (25 W m-*) slightly reduced nitrite oxidation while sunlight (628 W m-') decreased activity to ca 20 % of its original value. In addition, C O and CH, 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 C O inhibition are different for the NH: and NO; oxidizers examined. Characterization of light and C O responses by marine nitrifying bacteria is critical in any attempt to explain the formation of the subsurface primary nitrite maximum.