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 (MCF9T , MCF10T , and MCF14) and one of them to the genus Granulicella (MCF40T ). All isolates are moderately acidophilic (pH growth optimum 3.8-4.1) and mesophilic (temperature growth optima 30-32 °C). Isolates MCF10T and MCF40T 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, MCF9T , MCF10T , and MCF14 catalysed the reductive dissolution of the ferric iron mineral schwertmannite when incubated under micro-aerobic conditions. Isolates MCF9T 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 MCF10T , MCF9T , and MCF40T 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 MCF9T (=DSM 28997T  = NCCB 100575T ), Acidicapsa acidiphila strain MCF10T (=DSM 29819T  = NCCB 100576T ), and Granulicella acidiphila strain MCF40T (DSM 28996T  = NCCB 100577T ), are proposed.