Mixotrophic Growth Under Micro-Oxic Conditions in the Purple Sulfur Bacterium “Thiodictyon syntrophicum”

Abstract

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. It has been found that the purple sulfur bacterium “Thiodictyon syntrophicum” strain Cad16T, belonging to the Chromatiaceae, fixes around 26% of all bulk inorganic carbon in the chemocline, both during day and night. With this study, we elucidated for the first time the mode of carbon fixation of str. Cad16T under micro-oxic conditions with a combination of long-term monitoring of key physicochemical parameters with CTD, 14C-incorporation experiments and quantitative proteomics using in-situ dialysis bag incubations of str. Cad16T cultures. Regular vertical CTD profiling during the study period in summer 2017 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. CO2 assimilation rates were higher during the light period compared to those in the dark, both in the chemocline population and in the incubated cultures. The relative change in the proteome between day and night (663 quantified proteins) comprised only 1% of all proteins encoded in str. Cad16T. 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. Cad16T. 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 PXD010641.

Microbial loop of a Proterozoic ocean analogue

“…6 C-E). Previous studies reported a cyanobacterial bloom (28 August, 12 September 2017) at the oxic-anoxic transition directly above the phototrophic sulfur bacteria 36,37 ; however, cyanobacteria (Cyanobium, Gastranaerophilales, Pseudanabaena) were rare in this study.…”

“…6 C-E). Previous studies also reported cyanobacterial bloom (28 August, 12 September 2017) at the oxic-anoxic transition directly above the phototrophic sulfur bacteria 39,40 , however, cyanobacteria (Cyanobium, Gastranaerophilales, Pseudanabaena) were rare in this report. Furthermore, the shift 341 of oxygenic to anoxygenic photosynthesis is coincident with a decreasing efficiency of oxygenic 342 photosynthetic microbes (Fv/Fm), increasing concentrations of hydrogen sulfide, and a shift in bacterial abundance and beta-diversity (Fig.…”

Vertical structure of the bacterial diversity in meromictic Fayetteville Green Lake

“…The PSB sequences identified in FGL are affiliated with OTUs in the Chromatium , Thiodictyon , Thiocystis , and Lamprocystis genera (Figure 3a). PSB such as C. okenii , Thiocystis , and Thiodictyon syntrophicum all show some degree of tolerance to micro‐oxic conditions (Berg et al, 2019; Kampf & Pfennig, 1980; Luedin, Storelli, et al, 2019). The ability to tolerate and grow in micro‐oxic conditions may provide an advantage to the PSB in the shallower depths, which may be intermittently oxygenated, a condition that GSB are much less likely to tolerate.…”

Bacterial, phytoplankton, and viral dynamics of meromictic Lake Cadagno offer insights into the Proterozoic ocean microbial loop

“…The processes of the major microbial oxygenic and anoxygenic guilds have been reported to contribute almost equally to organic matter production in the Lake Cadagno chemocline (16), as they may have in ancient ocean chemoclines. Oxygenic (chlorophytes, diatoms, cyanobacteria) and anoxygenic phototrophs (PSB and GSB) coexisted in the Lake Cadagno chemocline (Figure 6C-E rectly above the phototrophic sulfur bacteria (33,34); however, cyanobacteria (Cyanobium, Gastranaerophilales, Pseudanabaena) were rare in this study. Furthermore, the shift of oxygenic to anoxygenic photosynthesis is coincident with a decreasing efficiency of oxygenic photosynthetic microbes (Fv/Fm), increasing concentrations of hydrogen sulfide, and a shift in bacterial abundance and beta-diversity (Figure 6F).…”