Quantification of Chlorosomal Bacteriochlorophylls Using Absorption Spectra of Green Sulfur Bacteria in Natural Water

A non-extraction method for determining the concentration of chlorosomal bacteriochlorophylls (Bchl), photosynthetic pigments of green sulfur bacteria has been developed and tested. The method is based on the measurement of optical density spectra of microorganisms directly in natural water and is aimed at simplifying Bchl concentration measurements, reducing the measurement time and eliminating toxic solvents from the experiments. Comparison of the results of Bchl concentration determination by the traditional method based on the measurement of absorption spectra of pigment extracts and the new method that is based on the measurement of long wavelength absorption band of Bchl in bacterial cells in natural water showed a high correlation coefficient from 0.9866 to 0.9991 for different series of samples. The depth distribution profiles of Bchl concentration obtained from the absorption spectra of natural water in some meromictic reservoirs of the White Sea region in September 2019 and Lake Mogilnoye (Barents Sea) in June 2019 are presented.