Figure 4

Comparison of the sulfur oxidation genes between the S. velum symbiont and other SOB. (a) Presence of genes involved in chemotrophic sulfur oxidation in the symbionts of S. velum, other sulfur-oxidizing bacteria and archaea, and sulfate reduction in D. autotrophicum, which is included for comparison. Genes encoding pathways for reverse-acting dissimilatory sulfur-oxidation (rDsr) (Drs in D. autotrophicum) and periplasmic sulfur-oxidation (Sox), as well as auxiliary proteins, are listed. Numbers of gene homologs in each organism are designated with color. Presence of extra- or intracellular sulfur deposits, i.e., globules, in each organism, as obtained from literature, is indicated with hollow circles. The abbreviations used, the respective full gene product names, and the corresponding NCBI protein ID references in the genome of the S. velum symbiont are listed in Additional file 3: Table S3. (b) Presence of signal sequences and transmembrane domains in the sulfur-oxidations genes of the S. velum symbiont, followed by the list of organisms with the closest known homologs to those genes and their respective BLASTP % identities (Avi - Allochromatium vinosum, Sup05 - uncultivated oxygen minimum zone microbe [42], Sli - Sideroxydans lithotrophicus, and Thia - Thiocapsa marina, Uncul - uncultured organism, Tsul - Thioalkalivibrio sulfidiphilus, Eper - R. pachyptila endosymbiont).