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Dependence of PRoteorhodopsin-phototrophy on specific dissolved Organic Matter compounds and their link to bacterial carbon cycling in the ocean (PROM)

Final Report Summary - PROM (Dependence of PRoteorhodopsin-phototrophy on specific dissolved Organic Matter compounds and their link to bacterial carbon cycling in the ocean (PROM))

Dependence of PRoteorhodopsin-phototrophy on specific dissolved Organic Matter compounds and their link to bacterial carbon cycling in the ocean (PROM)

Description of results obtained

The researcher has worked in collaboration with her supervisor at the host institution in order to assess the ecophysiological functions of proteorhodopsin (PR) phototrophy in bacteria with different life strategies under different specific substrate availability conditions.

1- Results from experiments with mono-specific cultures.
Results revealed light exposure could provide short-term beneficial effects for MED134. It was observed that PR phototrophy, depending on the physiological stage of the bacteria, could either result in increased growth or promote survival. The results also indicated that the benefit of PR phototrophy was greater when promoting survival than when increasing growth. MED134 did not show any substrate preferences between amino acids and glucose, but grew to higher abundance in the presence of both compared to either substrate alone or the control.

2- Experiments with natural bacterial assemblages.
Natural assemblages from the Baltic Sea were shown to positively respond in the short-term to organic carbon amedments (glucose) in the presence of nitrogen (ammonium) and phosphorus (phosphate)

3- Field studies.
Results from this study have shown a seasonal cycle on bacterial community composition and functioning in the two compartments studied (i.e. particle attached and free-living bacteria). Particle attached bacteria were more abundant and active coinciding with phytoplankton blooms periods and they were in general more efficient when processing organic matter than free-living bacteria.Transcriptomic analysis will help unravel the role of PR-phototrophy in these two compartments and relate it with substrate availability throughout the seasonal cycle. The reseracher is also collaborating as coauthor in the analysis of a large dataset recovered during the last years in the host group that will help understanding bacteria functioning in the Baltic sea throught the different seasons and that will set an exceptional background for her own work.

Potential impact and use
As explained above, the work preformed in this project aimed at exploring the tremendously important role that marine bacteria play in the biogeochemical cycling of essential elements and fluxes of energy. Dissolved organic carbon (DOC) derived from phytoplankton photosynthesis represents the main biologically available organic carbon pool in the ocean. Current estimates indicate that marine phytoplankton carry out half of the Earth’s photosynthesis, and around 50% of the organic carbon produced is channelled through bacteria. Bacteria play a key role in the turnover of DOC since they are the predominant organisms that readily assimilate or transform this source of reduced carbon in the sea. Consequently, marine bacteria play a central part in the global biogeochemical cycling of carbon, and are included in regional and global models to predict how carbon fluxes will respond to global change. In such models, bacteria are included as heterotrophic organisms (i.e. only as consumers of DOC) Considering the great scientific importance and broad-spectrum interest in understanding the role of light-harvesting molecules in the world’s biosphere, we believe that findings from this project are extremely relevant for the present scenario in the research field. We have gained understanding on the mechanisms of action of proteorhodpsin (PR) in marine bacteria and their efficiency, what can ultimately lead to models that can be used to predict or understand the effect of climate change and human actions on the marine carbon cycle and the productivity of the sea. Further, our results provide means to appreciate the sizeable biodiversity found among planktonic bacteria and how this biodiversity reflect different evolutionary adaptations to the natural environment. In addition, studies of the genetic basis for bacterial ecosystem function and microbial interactions have a substantial potential to identify novel enzymes, small molecules and proteins of importance to chemical industry, agriculture and medicine. Results from this project will unravel molecular mechanisms involved in carbon cycling, in general, and the interdependence of PR phototrophy and metabolism of key carbon compounds in marine bacteria, in particular. Specifically, to analyze and compare the PR- mediated metabolisms in bacteria that benefit differently from PR phototrophy is an extremely timely and relevant topic that promotes significant progress in the field.