Supplementary Material for: Comparative Genomic Analysis Reveals Novel Facts about <b><i>Leptospirillum</i></b> spp. Cytochromes

Chemolithoautotrophic acidophilic bacteria, which belong to the genus <i>Leptospirillum</i>, can only grow with Fe(II) as electron donor and oxygen as an electron acceptor. Members of this genus play an important role in bioleaching sulfide ores. We used nearly complete genome sequences of <i>Leptospirillum ferrooxidans</i> (group I), <i>Leptospirillum rubarum, Leptospirillum</i> ‘5-way CG’ (group II) and <i>Leptospirillum ferrodia</i><i>zotrophum</i> (group III) to identify cytochromes that are likely involved in electron transfer chain(s). The results show the presence of genes encoding a number of <i>c</i>-type cytochromes (18–20 genes were identified in each species), as well as <i>bd</i> and <i>cbb</i><sub><i>3</i></sub> oxidases. Genes encoding <i>cbb</i><sub><i>3</i></sub> oxidase are clustered, with predicted genes involved in <i>cbb</i><sub><i>3</i></sub> maturation proteins. Duplication of <i>cbb</i><sub><i>3</i></sub> encoding genes (<i>ccoNO)</i> was detected in all four genomes. Interestingly, these micro-organisms also contain genes that potentially encode <i>bc</i><sub><i>1 </i></sub><i>and b</i><sub><i>6</i></sub><i>f-like</i> complexes organized into two putative operon structures. To date, the <i>Leptospirillum </i>genus includes the only organisms reported to have genes coding for two different <i>bc </i>complexes. This study provides detailed insights into the components of electron transfer chains of <i>Leptospirillum</i> spp., revealing their conservation among leptospirilla groups and suggesting that there may be a single common pathway for electron transport between Fe(II) and oxygen.