Analysis of the Complete Genome of the Alkaliphilic and Phototrophic Firmicute Strain HH.

Despite significant interest and past work to elucidate the phylogeny and photochemistry of species of the , genomic analyses of heliobacteria to date have been limited to just one published genome, that of the thermophilic species (.) str. Ice1. Here we present an analysis of the complete genome of a second heliobacterium, () str. HH, an alkaliphilic, mesophilic, and morphologically distinct heliobacterium isolated from an Egyptian soda lake. The genome of is a single circular chromosome of 3.22 Mb with a GC content of 43.1% and 3263 protein-encoding genes. In addition to culture-based observations and insights gleaned from the genome an analysis of enzyme-encoding genes from key metabolic pathways supports an obligately photoheterotrophic lifestyle for . A complete set of genes encoding enzymes for propionate and butyrate catabolism and the absence of a gene encoding lactate dehydrogenase distinguishes the carbon metabolism of from its close relatives. Comparative analyses of key proteins in , including cytochrome and the F alpha subunit of ATP synthase, with those of related species reveal variations in specific amino acid residues that likely contribute to the success of in its highly alkaline environment.