The Origin of Nitrogen Fixation Genes in Cyanobacterium Acaryochloris marina

Biological nitrogen (N) fixation involves the reduction of atmospheric N2 to biologically available ammonia (NH3) and is performed by a wide variety of prokaryotic microorganisms. Fixed N is often the limiting nutrient in ecosystems; therefore, microorganisms that can fix N2, such as some cyanobacteria, are an important source of biologically available N in N-limited habitats. Acaryochloris marina is a Chlorophyll d-producing cyanobacterium that lives attached to red algae or colonial ascidians along the intertidal zone of marine environments. Through comparative genomics, we recently found that an A. marina clade consisting of three strains – GR1, MU08, and MU09 – possesses the ~20 nif genes required to perform N fixation, while all other A. marina strains lack these genes; they appear to have been acquired by horizontal transfer. Here, I performed phylogenetic analyses on these A. marina nif genes as well as those of related organisms to identify the potential donor(s). My study informs our understanding of the horizontal transfer of genes responsible for an important biological process

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