Microdiverse bacterial clades prevail across Antarctic wetlands

QUIROGA, M. V.; STEGEN, J.; MATALONI, G.; COWAN, D.A.; LEBRE, P.H.; VALVERDE, A.

Molecular Ecology

John Wiley and Sons Inc

Año: 2024 vol. 33

Antarctica´s extreme environmental conditions impose selection pressures on microbialcommunities. Indeed, a previous study revealed that bacterial assemblages at theCierva Point Wetland Complex (CPWC) are shaped by strong homogeneous selection.Yet which bacterial phylogenetic clades are shaped by selection processes and theirecological strategies to thrive in such extreme conditions remain unknown. Here, weapplied the phyloscore and feature-level βNTI indexes coupled with phylofactorizationto successfully detect bacterial monophyletic clades subjected to homogeneous(HoS) and heterogenous (HeS) selection. Remarkably, only the HoS clades showedhigh relative abundance across all samples and signs of putative microdiversity. Themajority of the amplicon sequence variants (ASVs) within each HoS clade clusteredinto a unique 97% sequence similarity operational taxonomic unit (OTU) and inhabiteda specific environment (lotic, lentic or terrestrial). Our findings suggest the existenceof microdiversification leading to sub-taxa niche differentiation, with putative distinctecotypes (consisting of groups of ASVs) adapted to a specific environment. Wehypothesize that HoS clades thriving in the CPWC have phylogenetically conservedtraits that accelerate their rate of evolution, enabling them to adapt to strong spatiotemporally variable selection pressures. Variable selection appears to operate withinclades to cause very rapid microdiversification without losing key traits that lead tohigh abundance. Variable and homogeneous selection, therefore, operate simultaneouslybut on different aspects of organismal ecology. The result is an overall signal ofhomogeneous selection due to rapid within-clade microdiversification caused by variableselection. It is unknown whether other systems experience this dynamic, and weencourage future work evaluating the transferability of our results.