The Oxidation of Hydrogen Sulfide by Beggiatoa

Knowledge of the conditions in which Beggiatoa is capable of autotrophic nutrition is incomplete. It is not known whether sulfur‐free trichomes from heterotrophic cultures are able to return to the utilization of H 2 S‐oxidation. Devices were developed which permitted the supply of pure cultures of Beggiatoa , previously cultivated heterotrophically, with H 2 S, O 2 , and CO 2 . Development in media devoid of organic nutrients was achieved, and subculturing under autotrophic conditions could be repeated indefinitely. The strains used behaved differently with respect to their tendency to grow autotrophically. The ability to dispense with organic substrates corresponds to the place in the groups to which they had previously been assigned. All the strains multiplied better when, under otherwise equal conditions, the inorganic medium was supplemented with acetate, very low concentrations of which were effective. This result may, however, be due to the selection of varieties by the isolation procedure. The mixotrophic tendency of our strains may not be a general feature of the genus. There are indications that the wider forms of Beggiatoa tend more toward autotrophic growth than the narrower ones.