Spectroscopic Study of Green Sulfur Bacteria in Stratified Water Bodies of the Kandalaksha Gulf of the White Sea

Resumo

Optical characteristics of water in stratified lakes of the White Sea are of particular interest in connection with the observation of thin colored layers resulting from massive development of anoxygenic phototrophic bacteria around the chemocline. While optical properties of chlorophyll are widely used in remote sensing, spectral characteristics of bacteriochlorophylls (BChl) for natural microbial communities have been little studied. In this work, spectral study of green sulfur bacteria of four water bodies of the Kandalaksha Gulf of the White Sea was carried out. Absorption and fluorescence spectra were measured for water samples taken in March 2017 from different depths and compared with spectra of monocultures isolated from the same water bodies earlier. It has been shown that the BChl fluorescence in the living cells of green sulfur bacteria has two overlapping emission bands: in the region of 740–770 nm (BChl d and e) and at 815 nm (BChl a). The wavelength of the maximum of the first band depends on the ratio of the concentrations of green- and brown-colored forms of bacteria containing different types of BChl. A new method for separating the contributions of two types of bacteria is proposed, based on the deconvolution of the BChl fluorescence spectrum into three bands whose parameters are determined from the spectra of monocultures. The BChl content at various water depths has been estimated and the percentage ratio of different types of phototrophic bacteria has been determined.