LIGHT-INDUCED ABSORBENCY CHANGES ASSOCIATED WITH PHOTOINHIBITION AND PIGMENTS IN NITRIFYING BACTERIA

Spectroscopic analysis of nitrifying bacteria revealed the presence of a porphyrin-like pigment with an absorption maximum at 408 nm. The ph otoresponsive pigment accumulated during the late exponential phase of growth. The photoreceptor was found at higher concentrations in NH4oxidizers than in NO2- oxidizers. When absorbance scans and action spe ctra of the nitrifiers were compared, it was found that the regression between the degree of photoinhibition and higher absorbances at 408 n m was significant (r(2) = 0.7). Reversible light-induced absorbance ch anges were observed in vivo and in vitro. Absorbance changes were maxi mally elicited by light in the 400 nm region for both types of nitrifi ers, but the change was only significant (p < 0.05] for NH4+ oxidizers . This spectral sensitivity of the NH4+ oxidizing process suggests tha t the absorbance change observed is related to the blue light sensitiv ity of NH4+ oxidizers.