Acidocella aromatica sp. nov.: an acidophilic heterotrophic alphaproteobacterium with unusual phenotypic traits

Three obligately heterotrophic bacterial isolates were identified as strains of a proposed novel species of extremely acidophilic, mesophilic Alphaproteobacteria, Acidocella aromatica. They utilized a restricted range of organic substrates, which included fructose (but none of the other monosaccharides tested), acetate and several aromatic compounds (benzoate, benzyl alcohol and phenol). No growth was obtained on complex organic substrates, such as yeast extract and tryptone. Tolerance of the proposed type strain of the species (PFBC) to acetic acid was much greater than that typically reported for acidophiles. The bacteria grew aerobically, and catalyzed the dissimilatory reductive dissolution of the ferric iron mineral schwertmannite under both micro-aerobic and anaerobic conditions. Strain PFBC did not grow anaerobically via ferric iron respiration, though it has been reported to grow in co-culture with acid-tolerant sulfidogenic bacteria under strictly anoxic conditions. Tolerance of strains of Acidocella aromatica to nickel were about two orders of magnitude greater than those of other Acidocella spp., though similar levels of tolerance to other metals tested was observed. The use of this novel acidophile in solid media designed to promote the isolation and growth of other (aerobic and anaerobic) acidophilic heterotrophs is discussed.