FEMS Microbiology Letters 81 (1991) 89-94 © 1991 Federation of European Microbiological Societies 0378-1097/91/$03.50 Published by Elsevier ADONIS 037810979100294D 89 FEMSLE 04490 An acid-stable cytochrome in iron-oxidizing Leptospirillum ferrooxidans A. Hart 1, J.C. Murrell 1, R.K. Poole 2 and P.R. Norris 1 Department of Biological Sciences, University of Warwick, Coventry and 2 Division of Biosphere Sciences, Kings College London, London, U.K. Received 19 February 1991 Accepted 11 March 1991 Key words: Leptospirillum ferrooxidans; Iron oxidation; Cytochrome 1. SUMMARY 2. INTRODUCTION A novel, apparently acid-stable cytochrome has been purified from Leptospirillum ferrooxidans in which it probably functions in the 'downhill' transfer of electrons from ferrous iron. It appeared to comprise a single polypeptide of apparent M r 17.9 kDa as determined by SDS-PAGE. Non-de- naturing PAGE showed this to be the approxi- mate size of the native protein. The oxidized cyto- chrome showed a broad absorption maximum at 422 nm and was readily reduced with dithionite or ferrous iron to give a form with absorption max- ima at 440 and 579 rim. A mid-point potential of +680 mV at pH 3.5 was determined. Iron and zinc were found at concentrations approaching one atom of each per cytochrome molecule. Correspondence to: P.R. Norris, Department of Biological Sci- ences, University of Warwick, Coventry CV4 7AL, U.K. Reduced iron, usually added to acidified media as ferrous sulphate or the metal moiety of mineral sulphides, is the only proven substrate for the growth of Leptospirillurn ferrooxidans. This acidophilic, autotrophic bacterium [1] appears to share the same habitats and (apart from its inabil- ity to oxidize sulphur) a similar physiology with the much more extensively studied iron-oxidizing acidophile, Thiobacillus ferrooxidans. However, these bacteria do not appear to be closely related on the basis of 16S rRNA analyses [2]. L. ferro- oxidans possesses a higher affinity for their com- mon substrate, ferrous iron, and is not so suscept- ible to inhibition by ferric iron [3]. These factors could explain the observed dominance of L. ferro- oxidans over T. ferrooxidans during the growth of initially mixed cultures of these bacteria in ferrous iron-limited chemostats [3]. The likelihood that differences in the iron oxidation systems of these bacteria underlie the distinctive responses to sub- strate (ferrous iron) and inhibitor (ferric iron) Downloaded from https://academic.oup.com/femsle/article-abstract/81/1/89/578247 by guest on 01 June 2020