Insights into the Fundamental Physiology of the Uncultured Fe-Oxidizing Bacterium Leptothrix ochracea.

is known for producing large volumes of iron oxyhydroxide sheaths that alter wetland biogeochemistry. For over a century, these delicate structures have fascinated microbiologists and geoscientists. Because still resists long-term culture, the debate regarding its metabolic classification dates back to 1885. We developed a novel culturing technique for using natural waters and coupled this with single-cell genomics and nanoscale secondary-ion mass spectrophotometry (nanoSIMS) to probe 's physiology. In microslide cultures doubled every 5.7 h and had an absolute growth requirement for ferrous iron, the genomic capacity for iron oxidation, and a branched electron transport chain with cytochromes putatively involved in lithotrophic iron oxidation. Additionally, its genome encoded several electron transport chain proteins, including a molybdopterin alternative complex III (ACIII), a cytochrome oxidase reductase, and several terminal oxidase genes. contained two key autotrophic proteins in the Calvin-Benson-Bassham cycle, a form II ribulose bisphosphate carboxylase, and a phosphoribulose kinase. also assimilated bicarbonate, although calculations suggest that bicarbonate assimilation is a small fraction of its total carbon assimilation. Finally, 's fundamental physiology is a hybrid of those of the chemolithotrophic type iron-oxidizing bacteria and the sheathed, heterotrophic filamentous metal-oxidizing bacteria of the genera. This allows to inhabit a unique niche within the neutrophilic iron seeps. was one of three groups of organisms that Sergei Winogradsky used in the 1880s to develop his hypothesis on chemolithotrophy. continues to resist cultivation and appears to have an absolute requirement for organic-rich waters, suggesting that its true physiology remains unknown. Further, is an ecological engineer; a few cells can generate prodigious volumes of iron oxyhydroxides, changing the ecosystem's geochemistry and ecology. Therefore, to determine 's basic physiology, we employed new single-cell techniques to demonstrate that oxidizes iron to generate energy and, despite having predicted genes for autotrophic growth, assimilates a fraction of the total CO that autotrophs do. Although not a true chemolithoautotroph, 's physiological strategy allows it to be flexible and to extensively colonize iron-rich wetlands.