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.
Keywords: Acidobacteria; Acidophile; Iron reduction; Metal-tolerance; Pit lakes.