ANOXYGENIC PHOTOSYNTHESIS IN THE BLACK SEA: DISTRIBUTION PATTERNS OF GREEN SULFUR BACTERIA USING PIGMENT-BASED APPROACHES

Date

2025-8

Author

Gülmez, Zeray Ayral

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Anoxygenic photosynthesis is an ancient biogeochemical pathway and a still potentially significant mechanism in some of the anoxic-sulfidic (euxinic) marine and lake ecosystems. A representative of this metabolism thrives in the Black Sea, the largest euxinic basin in the world. This study focuses on the distribution of an anoxygenic photosynthetic bacterium; Prosthecochloris sp. BS1, a green sulfur bacterium (GSB) strain with characteristically low light and metabolic requirements, inhabiting sulfidic depths. Detection, identification and comparative quantification of the bacterium were performed by pigment specific HPLC analysis that focused on the Bacteriochlorophyll e (BChl e) pigment. The only known carrier of the BChl e in the Black Sea is the Ptc. phaeobacteroides BS1 as supported by the genetic studies in the existing literature. Supported by the oceanographic and biogeochemical data retrieved during the R/V Bilim-2’s Black Sea Cruises in 2023 and 2024, this thesis researches the spatial and vertical distribution of the BChl e, and so, the Ptc. sp. BS1. A total of 125 samples were analyzed from 14 stations and the vertical distribution of the Bacteriochlorophyll e pigment homologues were obtained. A deeper peak was observed at the widely studied western basin, compared to previous studies. In the Eastern basin the population seems to be located at denser layers compared to Western basin. Especially inside the Batumi eddy, the deepest accumulation to be measured in the literature of the BChl e pigment was detected at 210 m. Overall, the findings support both active populations and also the persistence of the metabolically inactive population of BS1. Considering this primitive metabolism’s importance in understanding evolution of photosynthesis and past anoxic events, in addition to ongoing climate and habitability research in planetary sciences, it is believed that tracking this population’s distribution in the Black Sea will provide valuable insights for future specialized studies.

Subject Keywords

Black Sea, Green Sulfur Bacteria, Extreme Environment, Anoxygenic Photosynthesis, HPLC Pigment Analysis

URI

https://hdl.handle.net/11511/117406

Collections

Graduate School of Marine Sciences, Thesis