Insights into the biology of acidophilic members of the Acidiferrobacteraceae family derived from comparative genomic analyses

The family Acidiferrobacteraceae (order Acidiferrobacterales) currently contains Gram negative, neutrophilic sulfur oxidizers such as Sulfuricaulis and Sulfurifustis, as well as acidophilic iron and sulfur oxidizers belonging to the Acidiferrobacter genus. The diversity and taxonomy of the genus Acidiferrobacter has remained poorly explored. Although several metagenome and bioleaching studies have identified its presence worldwide, only two strains, namely Acidiferrobacter thiooxydans DSM 2932^T, and Acidiferrobacter spp. SP3/III have been isolated and made publically available.Using 16S rRNA sequence data publically available for the Acidiferrobacteraceae, we herein shed light into the molecular taxonomy of this family. Results obtained support the presence of three clades Acidiferrobacter, Sulfuricaulis and Sulfurifustis. Genomic analyses of the genome sequences of A. thiooxydans^T and Acidiferrobacter spp. SP3/III indicate that ANI relatedness between the SPIII/3 strain and A. thiooxydans^T is below 95–96%, supporting the classification of strain SP3/III as a new species within this genus. In addition, approximately 70% of Acidiferrobacter sp. SPIII/3 predicted genes have a conserved ortholog in A. thiooxydans strains. A comparative analysis of iron, sulfur oxidation pathways, genome plasticity and cell-cell communication mechanisms of Acidiferrobacter spp. are also discussed.