engleski

Contribution of green and purple sulfur bacteria to total inorganic carbon fixation in a sulfidic seawater lake

A clonal population of halotolerant purple sulfur bacteria (PSB) affiliated with the genus Halochromatium and an assemblage of Prosthecochloris-like green sulfur bacteria (GSB) are co-occurring in Lake Rogoznica, a holomictic, sulfidic seawater lake at the Adriatic coast. The GSB are the dominant microbial population (up to 89% of all cells) at the chemocline and in the hypolimnion. Despite being relatively rare (1-3%), the large Halochromatium–affiliated PSB can dominate the microbial biovolume, in particular at the chemocline depth. In this study, we used fluorescence-activated cell sorting (FACS) and scintillation counting to determine the relative contributions of GSB and PSB to total inorganic carbon fixation. We performed in situ 14C-bicarbonate incorporation experiments and determined 14C-uptake for GSB and PSB by combining autofluorescence and size-based FACS. In the April 2015, a PSB population was only detectable at the chemocline (9 m) and contributed little to total inorganic carbon fixation. GSB populations were similarly abundant both at the chemocline and in the hypolimnion (10 m). The GSB population sorted from chemocline samples corresponded to 18.4±1.4% of all cells and was responsible for almost the entire measurable inorganic carbon fixation in this water layer. In contrast, the GSB population sorted from the hypolimnion (19.7±6.4%) displayed no significant inorganic carbon assimilation. In conclusion, inorganic carbon fixation by anoxygenic photosynthesis in Lake Rogoznica seems to be almost exclusively linked to chemocline dwelling GSB.

GSB; PSB; carbon fixation

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