Bacterial isoprenoid quinones were used as tools for studying the bacterial community structure and population dynamics in photosynthetic sludge in a full-scale plant and a laboratory batch reactor. Both ubiquinones and menaquinones were detected from all sludge samples, at concentrations of 428 to 886 and 170 to 456 nmol/g (dry weight) of sludge, respectively. Smaller amounts of rhodo-quinones were also found in all sludges. Either ubiquinone-10 (Q-10) or Q-8 was the predominant ubiquinone in the main treatment zones of the plant, while Q-10 predominated in the laboratory sludge. The menaquinone composition of the sludges was more complicated than the ubiquinone profiles recorded. The plant and laboratory sludges contained menaquinone-9 (MK-9) and MK-10, respectively, as the major menaquinone. Bacteriological examination revealed the occurrence of high numbers of the purple nonsulfur bacteria in the photosynthetic sludge reactors. All strains of the phototrophic bacteria isolated from the sludges contained Q-10 as the sole quinone. These results suggest that Q-10 may be used as a biomarker of the phototrophic bacterial population, while other ubiquinones, menaquinones, and rhodoquinones may be useful for monitoring the population dynamics of co-existent chemoheterotrophic bacteria in the photosynthetic sludge process.

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