Uncovering a Microbial Enigma: Isolation and Characterization of the Streamer-Generating, Iron-Oxidizing, Acidophilic Bacterium “Ferrovum myxofaciens”

Abstract

ABSTRACTA betaproteobacterium, shown by molecular techniques to have widespread global distribution in extremely acidic (pH 2 to 4) ferruginous mine waters and also to be a major component of “acid streamer” growths in mine-impacted water bodies, has proven to be recalcitrant to enrichment and isolation. A modified “overlay” solid medium was devised and used to isolate this bacterium from a number of mine water samples. The physiological and phylogenetic characteristics of a pure culture of an isolate from an abandoned copper mine (“Ferrovum myxofaciens” strain P3G) have been elucidated. “F. myxofaciens” is an extremely acidophilic, psychrotolerant obligate autotroph that appears to use only ferrous iron as an electron donor and oxygen as an electron acceptor. It appears to use the Calvin-Benson-Bassham pathway to fix CO2and is diazotrophic. It also produces copious amounts of extracellular polymeric materials that cause cells to attach to each other (and to form small streamer-like growthin vitro) and to different solid surfaces. “F. myxofaciens” can catalyze the oxidative dissolution of pyrite and, like many other acidophiles, is tolerant of many (cationic) transition metals. “F. myxofaciens” and related clone sequences form a monophyletic group within theBetaproteobacteriadistantly related to classified orders, with genera of the familyNitrosomonadaceae(lithoautotrophic, ammonium-oxidizing neutrophiles) as the closest relatives. On the basis of the phylogenetic and phenotypic differences of “F. myxofaciens” and otherBetaproteobacteria, a new family, “Ferrovaceae,” and order, “Ferrovales,” within the classBetaproteobacteriaare proposed. “F. myxofaciens” is the first extreme acidophile to be described in the classBetaproteobacteria.