Bacterial, Archaeal, and Eukaryotic Life of Volcanic Cave Features from Lava Beds National Monument, California, USA

Volcanic caves present a variety of surfaces that host unique life, but most microbiology studies of these environments to date have focused on colorful and sometimes abundant biofilms, while largely ignoring ooze and hard secondary mineral deposits. In this study, we conducted 16S/18S rRNA gene sequencing with bacterial, archaeal, and eukaryotic domain-specific primer sets, focusing on a broad spectrum of volcanic cave features in Lava Beds National Monument grouped into ‘microbial-dominant’ (biofilms and ooze) and ‘mineral-dominant’ (secondary mineral deposits). While there are differences between individual mineral-dominant features, collectively, microbial communities associated with these features are distinct from those of microbial-dominant based on prokaryotic beta diversity metrics. Mineral-dominant features are not merely a subset of the microbial-dominant owing to their similar alpha diversity scores and unique ASVs. Ooze is distinct from all other categories due to the near absence of otherwise abundant Actinobacteriota and abundance of taxa associated with roles in ammonia and nitrite oxidation. Differences in eukaryotic communities were associated with the sampling year rather than feature type, suggesting that cave eukaryotes have a more transient lifestyle than prokaryotes. Overall, these results provide evidence that mineral-dominant features and ooze are microbiologically distinct from more-often-studied cave biofilms.