Phylogeny and phenotypic characterization of the stalk-forming and iron-oxidizing bacterium Gallionella ferruginea

The 16S rRNA gene of Gallionella ferruginea was amplified by polymerase chain reaction and sequenced by direct double-stranded sequencing. The phylogenetic analysis placed G. ferruginea in the beta-group of the Proteobacteria, with 90.0% similarity to Nitrosolobus multiformis and 88.6% to Rhodocyclus purpureus. The published phenotypic characteristics of G. ferruginea were compiled and supplemented with growth experiments using ferrous iron, thiosulphate and sulphide as electron donor, and nitrate as nitrogen source. G. ferruginea is a Gram-negative, curved bacterium with one polar flagellum. It grows auto- and mixotrophically with CO2, glucose, fructose and sucrose as carbon sources, ferrous iron as an electron donor and ammonium or nitrate as nitrogen sources. Two G. ferruginea specific oligonucleotide probes are suggested. An iron-oxidizing bacterium without stalk-forming ability, but with the same growth pattern as G. ferruginea, was identified as G. ferruginea by comparison of highly variable parts of the 16S rRNA gene. This indicates that the stalk is not essential for growth.