Acidicapsa ferrireducens sp. nov., Acidicapsa acidiphila sp. nov., and Granulicella acidiphila sp. nov.: novel acidobacteria isolated from metal-rich acidic waters.

Four novel strains of Acidobacteria were isolated from water samples taken from pit lakes at two abandoned metal mines in the Iberian Pyrite Belt mining district, south-west Spain. Three of the isolates belong to the genus Acidicapsa (MCF9, MCF10, and MCF14) and one of them to the genus Granulicella (MCF40). All isolates are moderately acidophilic (pH growth optimum 3.8-4.1) and mesophilic (temperature growth optima 30-32 °C). Isolates MCF10 and MCF40 grew at pH lower (<3.0) than previously reported for all other acidobacteria. All four strains are obligate heterotrophs and metabolised a wide range of sugars. While all four isolates are obligate aerobes, MCF9, MCF10, and MCF14 catalysed the reductive dissolution of the ferric iron mineral schwertmannite when incubated under micro-aerobic conditions. Isolates MCF9 and MCF14 shared 99.5% similarity of their 16 S rRNA genes, and were considered to be strains of the same species. The major quinone of strains MCF10, MCF9, and MCF40 is MK-8, and their DNA G + C contents are 60.0, 59.7, and 62.1 mol%, respectively. Based on phylogenetic and phenotypic data, three novel species, Acidicapsa ferrireducens strain MCF9 (=DSM 28997 = NCCB 100575), Acidicapsa acidiphila strain MCF10 (=DSM 29819 = NCCB 100576), and Granulicella acidiphila strain MCF40 (DSM 28996 = NCCB 100577), are proposed.