Light-induced absorbance changes associated with photoinhibition and pigments in nitrifying bacteria

Abstract

Spectroscopic analysis of nitrifying bacteria revealed the presence of a porphyrin-like pigment with an absorption maximum at 408 nm. The photoresponsive pigment accumulated during the late exponential phase of growth. The photoreceptor was found at higher concentrations in NH4+ oxidizers than in NO2oxldizers. When absorbance scans and action spectra of the nitrifiers were compared, it was found that the regression between the degree of photoinhibition and higher absorbances at 408 nm was significant (r2 = 0.7). Reversible light-induced absorbance changes were observed in vivo and in vitro. Absorbance changes were maximally elicited by light in the 400 nm region for both types of nitrifiers, but the change was only significant (p < 0.05) for NH,' oxldizers. This spectral sensitivity of the NH,' oxidizing process suggests that the absorbance change observed is related to the blue light sensitivity of NH,+ oxidizers.