The reaction center-light harvesting 1 (RC-LH1) complex converts solar energy into electrical energy, driving the initiation of photosynthesis. The authors present a cryo-electron microscopy structure of the RC-LH1 isolated from a marine photoheterotrophic bacterium Dinoroseobacter shibae. The RC comprises four subunits, including a three-heme cytochrome (Cyt) c protein, and is surrounded by a closed LH ring composed of 17 pairs of antenna subunits. Notably, a novel subunit with an N-terminal "helix-turn-helix" motif embedded in the gap between the RC and the LH ring is identified. The purified RC-LH1 complex exhibits high stability in solutions containing Mg2+ or Ca2+. The periplasmic Cyt c2 is predicted to bind at the junction between the Cyt subunit and the membrane plane, enabling electron transfer from Cyt c2 to the proximal heme of the tri-heme Cyt, and subsequently to the special pair of bacteriochlorophylls. These findings provide structural insights into the efficient energy and electron transfer processes within a distinct type of RC-LH1, and shed light on evolutionary adaptations of photosynthesis.

• Klíčová slova
• energy transfer, photoheterotrophic bacteria, photosynthesis, reaction center, structure,
• MeSH
• bakteriální proteiny metabolismus   chemie   MeSH
• elektronová kryomikroskopie metody   MeSH
• fotosyntéza fyziologie   MeSH
• hem metabolismus   chemie   MeSH
• světlosběrné proteinové komplexy * metabolismus   ultrastruktura   chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• hem MeSH
• světlosběrné proteinové komplexy * MeSH

The model organism Dinoroseobacter shibae and many other marine Rhodobacterales (Roseobacteraceae, Alphaproteobacteria) are characterized by a multipartite genome organization. Here, we show that the original isolate (Dshi-6) contained six extrachromosomal replicons (ECRs), whereas the strain deposited at the DSMZ (Dshi-5) lacked a 102-kb plasmid. To determine the role of the sixth plasmid, we investigated the genomic and physiological differences between the two strains. Therefore, both genomes were (re)sequenced, and gene expression, growth, and substrate utilization were examined. For comparison, we included additional plasmid-cured strains in the analysis. In the Dshi-6 population, the conjugative 102-kb RepABC-9 plasmid was present in only about 50% of the cells, irrespective of its experimentally validated stability. In the presence of the sixth plasmid, copy number changes of other ECRs, in particular, a decrease of the 86-kb plasmid, were observed. The most conspicuous finding was the strong influence of plasmids on chromosomal gene expression, especially the repression of the CtrA regulon and the activation of the denitrification gene cluster. Expression is inversely controlled by either the presence of the 102-kb plasmid or the absence of the 86-kb plasmid. We identified regulatory genes on both plasmids, i.e., a sigma 70 factor and a quorum sensing synthase, that might be responsible for these major changes. The tremendous effects that were probably even underestimated challenge the current understanding of the relevance of volatile plasmids not only for the original host but also for new recipients after conjugation. IMPORTANCE Plasmids are small DNA molecules that replicate independently of the bacterial chromosome. The common view of the role of plasmids is dominated by the accumulation of resistance genes, which is responsible for the antibiotic crisis in health care and livestock breeding. Beyond rapid adaptations to a changing environment, no general relevance for the host cell's regulome was attributed to these volatile ECRs. The current study shows for the model organism D. shibae that its chromosomal gene expression is strongly influenced by two plasmids. We provide evidence that the gain or loss of plasmids not only results in minor alterations of the genetic repertoire but also can have tremendous effects on bacterial physiology. The central role of some plasmids in the regulatory network of the host could also explain their persistence despite fitness costs, which has been described as the "plasmid paradox."

• Klíčová slova
• CtrA regulon, Roseobacteraceae, denitrification, heavy metal resistance, plasmid stability, transcriptomics,
• MeSH
• exprese genu MeSH
• plazmidy genetika   MeSH
• replikon genetika   MeSH
• Rhodobacteraceae * genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The roseobacter group of marine bacteria is characterized by a mosaic distribution of ecologically important phenotypes. These are often encoded on mobile extrachromosomal replicons. So far, conjugation had only been experimentally proven between the two model organisms Phaeobacter inhibens and Dinoroseobacter shibae. Here, we show that two large natural RepABC-type plasmids from D. shibae can be transferred into representatives of all known major Rhodobacterales lineages. Complete genome sequencing of the newly established Phaeobacter inhibens transconjugants confirmed their genomic integrity. The conjugated plasmids were stably maintained as single copy number replicons in the genuine as well as the new host. Co-cultivation of Phaeobacter inhibens and the transconjugants with the dinoflagellate Prorocentrum minimum demonstrated that Phaeobacter inhibens is a probiotic strain that improves the yield and stability of the dinoflagellate culture. The transconjugant carrying the 191 kb plasmid, but not the 126 kb sister plasmid, killed the dinoflagellate in co-culture.

• Klíčová slova
• Roseobacter, bacteria–algae interaction, conjugation, horizontal gene transfer,
• MeSH
• Dinoflagellata * genetika   MeSH
• plazmidy genetika   MeSH
• replikon MeSH
• Rhodobacteraceae MeSH
• Roseobacter * genetika   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.

• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• fototrofní procesy MeSH
• fylogeneze MeSH
• molekulární sekvence - údaje MeSH
• operon * MeSH
• přenos genů horizontální * MeSH
• Roseobacter klasifikace   genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH