Aerobic anoxygenic photosynthetic bacteria are an important component of marine microbial communities. They produce energy in light using bacteriochlorophyll a containing photosystems. This extra energy provides an advantage over purely heterotrophic bacteria. One of the most intensively studied AAP bacteria is Dinoroseobacter shibae, a member of the environmentally important Roseobacter clade. Light stimulates its growth and metabolism, but the effect of light intensity remains unclear. Here, we show that an increase in biomass along an irradiance gradient followed the exponential rise to the maximum curve, with saturation at about 300 µmol photons m-2 s-1 , without any inhibition at light intensities up to 600 µmol photons m-2 s-1 . The cells adapted to higher irradiance by reducing pigmentation and increasing the electron transfer rate. This additional energy allowed D. shibae to redirect the metabolism of organic carbon sources such as glucose, leucine, glutamate, acetate and pyruvate toward anabolism, resulting in a twofold increase of their assimilation rates. We provide equations that can be feasibly incorporated into the existing model of D. shibae metabolism to further advance our understanding of the role of photoheterotrophy in the ocean.
- MeSH
- bakteriochlorofyl A metabolismus MeSH
- biomasa MeSH
- energetický metabolismus fyziologie MeSH
- fotosyntéza fyziologie MeSH
- organické látky metabolismus MeSH
- Roseobacter metabolismus MeSH
- světlo MeSH
- transport elektronů fyziologie MeSH
- vodní organismy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The Roseobacter clade represents one of the most important bacterial groups in marine environments. While some of its members are heterotrophs, many Roseobacter clade members contain bacterial photosynthetic reaction centers. We investigated the phylogeny of pufL and pufM genes encoding the L and M subunits of reaction centers using available genomic data and our own cultured species. Interestingly, phylogeny of pufL and pufM genes largely deviated from 16S rRNA-based phylogeny. The sequences split into two clearly distinct clades. While most of the studied species contained pufL and pufM sequences related to those found in Roseobacter litoralis, some of the marine species contained sequences related to the freshwater Rhodobacter species. In addition, genomic data documents that Roseobacter-type centers contain cytochrome c subunits (pufC gene product), whereas Rhodobacter-type centers incorporate PufX proteins. This indicates that the two forms of the reaction centers are not only distinct phylogenetically, but also structurally. The large deviation of pufL and pufM phylogeny from 16S phylogeny indicates multiple horizontal transfers of the puf operon among members of the order Rhodobacterales.
