Anaerobic transformation of halocarboxylic acids and phenolic compounds by photosynthetic bacteria

Abstract

The ability of photosynthetic bacteria to transform phenolic compounds and halocarboxylic acids under photoheterotrophic growth conditions was assessed and studied. Attempts to isolate strains of phototrophic bacteria capable of degrading phenolic compounds yielded a strain of the purple nonsulfur bacteria species Rhodopseudomonas palustris. The isolated strain showed growth to a high cell density on phenol, although this may have been in conjunction with a sulfate reducing bacteria. Certain type strains of purple nonsulfur bacteria were able to grow on phenol and a small number of substituted phenols. Rhodospirillum rubrum DSM 467 showed growth to a high cell density on the pesticide 2,4- dinitrophenol at a concentration of 1.5 mM. The initial step in the degradation was shown to be a reduction of the ortho-nitro group to an amino group, transforming the compound to 2-amino-4-nitrophenol.

A number of purple nonsulfur bacteria type strains were reported for the first time to utilise halocarboxylic acids for photoheterotrophic growth. Growth rates and optimum growth concentrations increased when cells were previously adapted for growth on the halocarboxylic acid substrates. Collectively, the purple nonsulfur bacteria can grow at the expense of brominated, chlorinated, and fluorinated acetic and propionic acids. The mechanism of degradation was shown to be via reductive dehalogenation. The results suggest that the purple nonsulfur bacteria may play a significant role in the transformation of phenolic and halogenated compounds in anaerobic sediments, particularly in cases of heavy contamination where the ability of these bacteria to grow on high concentrations of these compounds could allow them to proliferate.