Bringing microbial diversity into focus: high-resolution analysis of iron mats from the Lō'ihi Seamount

Thirty kilometers south of the island of Hawai'i lies the Lō'ihi Seamount, an active submarine volcano that hosts a network of low-temperature hydrothermal vents enriched in ferrous iron that supports extensive microbial mats. These mats, which can be a half a meter deep, are composed of ferric iron bound to organic polymers - the metabolic byproduct of iron-oxidizing Zetaproteobacteria. Though the role of Zetaproteobacteria in mat formation is well established, we have a limited understanding of how differences in diversity are related to mat morphology. We used Minimum Entropy Decomposition and ZetaOtu classification to demonstrate cryptic diversity between closely related Zetaproteobacteria while showing habitat and geographic specificity. Veiled mats, common structures at Lō'ihi, exhibit distinct community composition and contain diversity not detected in other mat types, including specific Zetaproteobacteria and an unclassified Gammaproteobacteria. Our analyses also indicate that diversity can change dramatically across small spatial transects from points of active venting, yet we found comparatively few differences between major sampling sites. This study provides a better picture of the microbiome responsible for iron mat production at Lō'ihi and has broad implications for our understanding of these globally distributed communities.