Metabolic Versatility in Melainabacteria, a Close Relative of Cyanobacteria

A New Member of Melainabacteria, the Closest Relatives of Cyanobacteria Melainabacteria are the recently discovered, closest non-photosynthetic relatives of cyanobacteria, the organisms responsible for the oxygenation of Earth\u27s atmosphere. Previous work has shown that Melainabacteria live in a wide range of environments, including deep groundwater, anoxic sediments, and the digestive tracts of termites and mammals. These bacteria have been suggested to play a significant role in the latter environments and may contribute to neurodegenerative and gastrointestinal disease in human populations. However, our knowledge of Melainabacteria diversity and metabolism is still very limited, principally because no member of this group has been successfully cultured in the laboratory. Recently, DNA sequencing has revealed that a member of the Melainabacteria is growing in co-culture with an established diatom strain at the University of Montana’s Miller lab. In this study, we obtained a nearly complete Melainabacteria genome from metagenomic sequencing data. We then compared this genome to other previously sequenced Melainabacteria genomes to better understand genome architecture and the metabolic capacity of this bacterium. These data will guide further culturing efforts and future experiments. Together, our work will help clarify the functional role(s) of Melainabacteria in its environment and how it “makes a living” energetically. It will also provide new insights regarding the metabolic capabilities of the cyanobacterial ancestor and the origin of oxygenic photosynthesis

Rapid Evolution of the Rhopalodia gibba Mitochondrion in the Presence of an Emerging Nitrogen Fixing Organelle

The evolution of the mitochondrion from an endosymbiotic bacterium was the defining moment in the origin of eukaryotes. This understanding is based on multiple evolutionary studies that show that some organelles, such as mitochondria and chloroplasts, evolved from endosymbionts. Yet, understanding the process of organelle evolution remains one of the grand challenges in biology. Although several host-microbe relationships have been studied as key steps in organelle evolution, these examples typically focus on later stages of this process. The diatoms in the genera Rhopalodia, Epithemia, and Denticula have nitrogen fixing cyanobacterial endosymbionts called spheroid bodies, which are proposed to be emerging organelles. Understanding this diatom-spheroid body relationship provides an important model of that can provide insight into the early stages of how organelles evolve. To understand this system, we obtained genome data for the spheroid body as well as the first genome data for the host, Rhopalodia gibba. We are using these data to investigate evolutionary changes in spheroid body and host genomes during the development of the symbiosis as well as to serve as references for mapping gene expression data. In this study, we compared the genome of the R. gibba organelles to other closely related diatom species that don’t have spheroid bodies. Analyses show that the chloroplast genome is changing at a similar rate compared to related diatoms. However, selection on the R. gibba mitochondrion appears to be relaxed. Translational genes appear to be changing at an increased rate compared to energy production genes. Additionally, horizontal gene transfer also contributes to mitochondrial divergence. This diatom-spheroid body relationship provides a rare opportunity to quantify these benefits and costs and could help elucidate the mechanisms of organelle evolution

Bibliographie zu Informations- und Kommunikationstechnologien

UuStB Koeln=38*-900106688 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Genomic and Functional Variation of the Chlorophyll d-Producing Cyanobacterium Acaryochloris marina

The Chlorophyll d-producing cyanobacterium Acaryochloris marina is widely distributed in marine environments enriched in far-red light, but our understanding of its genomic and functional diversity is limited. Here, we take an integrative approach to investigate A. marina diversity for 37 strains, which includes twelve newly isolated strains from previously unsampled locations in Europe and the Pacific Northwest of North America. A genome-wide phylogeny revealed both that closely related A. marina have migrated within geographic regions and that distantly related A. marina lineages can co-occur. The distribution of traits mapped onto the phylogeny provided evidence of a dynamic evolutionary history of gene gain and loss during A. marina diversification. Ancestral genes that were differentially retained or lost by strains include plasmid-encoded sodium-transporting ATPase and bidirectional NiFe-hydrogenase genes that may be involved in salt tolerance and redox balance under fermentative conditions, respectively. The acquisition of genes by horizontal transfer has also played an important role in the evolution of new functions, such as nitrogen fixation. Together, our results resolve examples in which genome content and ecotypic variation for nutrient metabolism and environmental tolerance have diversified during the evolutionary history of this unusual photosynthetic bacterium