FIG. 3.

Schematic representation of hydrogenase and photosynthesis gene clusters in H. modesticaldum. Arrows represent individual genes and indicate the direction of transcription. (A) Putative [FeFe] hydrogenase genes in H. modesticaldum and the close phylogenetic relative P. thermopropionicum SI. As in Heliobacillus mobilis, nuoE and nuoF are fused in H. modesticaldum, suggesting that this feature may be universal in heliobacteria. Colors indicate the following: gold, NADH dehydrogenase subunits; orange, [FeFe] hydrogenase structural genes. (B) Uptake [NiFe] hydrogenase genes in related Firmicutes. The genes are located in a single operon in H. modesticaldum, whereas they are dispersed in different regions of the D. hafniense Y51 chromosome. Colors indicate the following: blue, [NiFe] hydrogenase structural genes; purple, hydrogenase expression/formation; red, hydrogenase assembly/maturation. (C) Photosynthesis gene clusters from H. modesticaldum and the purple bacterium R. capsulatus. Shared genes are outlined with bold lines. Lines indicate gene synteny, as follows: black lines, single gene rearrangements; red lines, inverted genes; blue lines, inverted genes with a gene insertion. Dashed boxes indicate R. capsulatus photosynthesis genes absent from H. modesticaldum. The colors of the arrows indicate the following: green, Bchl biosynthesis (bch); orange, carotenoid biosynthesis (crt); pink, proteobacterial reaction centers (puf) and light harvesting complexes (puh); olive, heliobacterial reaction center (psh); teal, regulatory proteins; light green, electron transport (pet); red, cofactor biosynthesis; purple, cell division and sporulation; light blue, nitrogen fixation; gray, transcription; light gray, other nonphotosynthetic genes; white, uncharacterized genes.