<i>Leptothrix ochracea</i> genomes reveal potential for mixotrophic growth on Fe(II) and organic carbon

Winogradsky's observations of <i>L. ochracea</i> led him to propose autotrophic iron oxidation as a new microbial metabolism, following his work on autotrophic sulfur-oxidizers. While much culture-based research has ensued, isolation proved elusive, so most work on <i>L. ochracea</i> has been based in the environment and in microcosms. Meanwhile, the autotrophic <i>Gallionella</i> became the model for freshwater microbial iron oxidation, while heterotrophic and mixotrophic iron oxidation is not well-studied. Ecological studies have shown that <i>Leptothrix</i> overtakes <i>Gallionella</i> when dissolved organic carbon content increases, demonstrating distinct niches. This study presents the first near-complete genomes of <i>L. ochracea</i>, which share some features with autotrophic iron oxidizers, while also incorporating heterotrophic metabolisms. These genome, metabolic modeling, and transcriptome results give us a detailed metabolic picture of how the organism may combine lithoautotrophy with organoheterotrophy to promote Fe oxidation and C cycling and drive many biogeochemical processes resulting from microbial growth and iron oxyhydroxide formation in wetlands.