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The microbial ecosystem of the meromictic Lake Cadagno Ticino, Swiss Alps has been studied intensively in order to understand structure and functioning of the anoxygenic phototrophic sulfur bacteria community living in the chemocline. With this study, we elucidated for the first time the mode of carbon fixation of str. Cad16 T under micro-oxic conditions with a combination of long-term monitoring of key physicochemical parameters with CTD, 14 C-incorporation experiments and quantitative proteomics using in-situ dialysis bag incubations of str.
Cad16 T cultures. Regular vertical CTD profiling during the study period in summer revealed that the chemocline sank from 12 to 14 m which was accompanied by a bloom of cyanobacteria and the subsequent oxygenation of the deeper water column. Sampling was performed both day and night. CO 2 assimilation rates were higher during the light period compared to those in the dark, both in the chemocline population and in the incubated cultures.
Cad16 T. Oxidative respiration pathways were upregulated at light, whereas stress-related mechanisms prevailed during the night. These results indicate that low light availability and the co-occurring oxygenation of the chemocline induced mixotrophic growth in str.
Our study thereby helps to further understand the consequences micro-oxic conditions for phototrophic sulfur oxidizing bacteria. The complete proteome data have been deposited to the ProteomeXchange database with identifier PXD Keywords: sulfur cycling, carbon fixation, meromixis, Lake Cadagno, mixotrophic growth, purple sulfur batceria.
