Parapatric speciation of Meiothermus in serpentinite-hosted aquifers in Oman

Microbial ecology of serpentinite-hosted ecosystems

Serpentinization, the collective set of geochemical reactions initiated by the hydration of ultramafic rock, has occurred throughout Earth history and is inferred to occur on several planets and moons in our solar system. These reactions generate highly reducing conditions that can drive organic synthesis reactions potentially conducive to the emergence of life, while concomitantly generating fluids that challenge life owing to hyperalkalinity and limited inorganic carbon (and oxidant) availability. Consequently, the serpentinite-hosted biosphere offers insights into the earliest life, the habitable limits for life, and the potential for life on other planets. However, the support of abundant microbial communities by serpentinites was only recognized ~20 years ago with the discovery of deep-sea hydrothermal vents emanating serpentinized fluids. Here, we review the microbial ecology of both marine and continental serpentinization-influenced ecosystems in conjunction with a comparison of publicly available metagenomic sequence data from these communities to provide a global perspective of serpentinite microbial ecology. Synthesis of observations across global systems reveal consistent themes in the diversity, ecology, and functioning of communities. Nevertheless, individual systems exhibit nuances due to local geology, hydrology, and input of oxidized, near-surface/seawater fluids. Further, several new (and old) questions remain including the provenance of carbon to support biomass synthesis, the physical and chemical limits of life in serpentinites, the mode and tempo of in situ evolution, and the extent that modern serpentinites serve as analogs for those on early Earth. These topics are explored from a microbial perspective to outline key knowledge-gaps for future research.

Viral communities in a pH>10 serpentinite-like environment: insight into diversity and potential roles in modulating the microbiomes by bioactive vitamin B9 synthesis

Viral communities exist in a variety of ecosystems and play significant roles in mediating biogeochemical processes, whereas viruses inhabiting strongly alkaline geochemical systems remain underexplored. In this study, the viral diversity, potential functionalities, and virus-host interactions in a strongly alkaline environment (pH = 10.4-12.4) exposed to the leachates derived from the serpentinization-like reactions of smelting slags were investigated. The viral populations (e.g., Herelleviridae, Queuovirinae, and Inoviridae) were closely associated with the dominating prokaryotic hosts (e.g., Meiothermus, Trueperaceae, and Serpentinomonas) in this ultrabasic environment. Auxiliary metabolic genes (AMGs) suggested that viruses may enhance hosts' fitness by facilitating cofactor biosynthesis, hydrogen metabolism, and carbon cycling. To evaluate the activity of synthesis of essential cofactor vitamin B9 by the viruses, a viral folA (vfolA) gene encoding dihydrofolate reductase (DHFR) was introduced into a thymidine-auxotrophic strain Escherichia coli MG1655 ΔfolA mutant, which restored the growth of the latter in the absence of thymidine. Notably, the homologs of the validated vDHFR were globally distributed in the viromes across various ecosystems. The present study sheds new light on the unique viral communities in hyperalkaline ecosystems and their potential beneficial impacts on the coexisting microbial consortia by supplying essential cofactors.

IMPORTANCE

This study presents a comprehensive investigation into the diversity, potential functionalities, and virus-microbe interactions in an artificially induced strongly alkaline environment. Functional validation of the detected viral folA genes encoding dihydrofolate reductase substantiated the synthesis of essential cofactors by viruses, which may be ubiquitous, considering the broad distribution of the viral genes associated with folate cycling.