Morphological Variation in Ferrobacillus Ferrooxidans related to the Rate of Iron Oxidation

WHILE investigating the removal of pyritic sulphur from coal by a microbiological method, we propagated large numbers of the chemoautotrophic iron-oxidizing bacterium Ferrobacillus ferrooxidans . During mass culture of the bacterium in an inorganic iron salts medium (9 K ) 1 , it was observed that alterations in cellular morphology occurred in response to excessively vigorous aeration. Normal cells measure 1.0–1.7µ by 0.5µ (Fig. 1 A ), while the abnormal (morphologically altered) cells differed by having a diameter of 1.0µ, so that many enlarged, coccoidal forms were present (Fig. 1 B ). The abnormal strain, on large-scale sub-culture using less vigorous aeration, or in shake-culture flasks, showed virtually complete reversion to the normal morphology after the second transfer (Fig. 1 C , D ).