Photoinhibition and recovery of NH4+-oxidizing bacteria and NO2--oxidizing bacteria.

Abstract

The effects of illumination on nitrifying bacteria were investigated with and without substrate. NH4+-oxidizing bacteria (strain H-1, probably Nitrosospira sp.) and NO2--oxidizing bacteria (strain O-1, probably Nitrobacter sp.), isolated from Lake Kizaki, were inhibited by light (about 75μEinsteins/m2/sec, 12-hr light: 12-hr dark). Photoinhibited H-1 and O-1 cells recovered after several to tens of days under dark conditions. However, H-1 cells, illuminated for 7 to 10 days in the absence of NH4+, did not produce NO2- significantly for 120 to 350 days in a medium containing 50uM NH4+. The substrate (NH4+) was found to protect H-1 from photoinhibition, while such an effect of NO2- on O-1 was not so clear. O-1 was more sensitive to light than H-1 in the short illumination period. However, the inhibitory effect of prolonged illumination was greater on H-1 than on O-1. It was indicated from growth kinetic analysis that the photoinhibitory effects on both NH4+-oxidizing bacteria and NO2--oxidizing bacteria were not only lethal but also bacteriostatic.