Comparative Genome Analysis Provides Insights into Both the Lifestyle of Strain CF27 and the Chimeric Nature of the Iron-Oxidizing Acidithiobacilli Genomes.

The iron-oxidizing species is one of few acidophiles able to oxidize ferrous iron and reduced inorganic sulfur compounds at low temperatures (<10°C). To complete the genome of strain CF27, new sequences were generated, and an update assembly and functional annotation were undertaken, followed by a comparative analysis with other species whose genomes are publically available. The CF27 genome comprises a 3,409,655 bp chromosome and a 46,453 bp plasmid. CF27 possesses genes allowing its adaptation to cold, metal(loid)-rich environments, as well as others that enable it to sense environmental changes, allowing CF27 to escape hostile conditions and to move toward favorable locations. Interestingly, the genome of CF27 exhibits a large number of genomic islands (mostly containing genes of unknown function), suggesting that a large number of genes has been acquired by horizontal gene transfer over time. Furthermore, several genes specific to CF27 have been identified that could be responsible for the phenotypic differences of this strain compared to other species. Most genes located inside CF27-specific gene clusters which have been analyzed were expressed by both ferrous iron-grown and sulfur-attached cells, indicating that they are not pseudogenes and may play a role in both situations. Analysis of the taxonomic composition of genomes of the Acidithiobacillia infers that they are chimeric in nature, supporting the premise that they belong to a particular taxonomic class, distinct to other proteobacterial subgroups.