Extremely halophilic archaeal communities are resilient to short-term entombment in halite.

Tom J C Huby,Terry J Mcgenity,Boyd A Mckew,Dave R Clark

doi:10.1111/1462-2920.14913

Abstract

SummarySome haloarchaea avoid the harsh conditions present in evaporating brines by entombment in brine inclusions within forming halite crystals, where a subset of haloarchaea survives over geological time. However, shifts in the community structure of halite‐entombed archaeal communities remain poorly understood. Therefore, we analysed archaeal communities from in situ hypersaline brines collected from Trapani saltern (Sicily) and their successional changes in brines versus laboratory‐grown halite over 21 weeks, using high‐throughput sequencing. Haloarchaea were dominant, comprising >95% of the archaeal community. Unexpectedly, the OTU richness of the communities after 21 weeks was indistinguishable from the parent brine and overall archaeal abundance in halite showed no clear temporal trends. Furthermore, the duration of entombment was less important than the parent brine from which the halite derived in determining the community composition and relative abundances of most genera in halite‐entombed communities. These results show that halite‐entombed archaeal communities are resilient to entombment durations of up to 21 weeks, and that entombment in halite may be an effective survival strategy for near complete communities of haloarchaea. Additionally, the dominance of ‘halite specialists’ observed in ancient halite must occur over periods of years, rather than months, hinting at long‐term successional dynamics in this environment.

Highlights

Hypersaline ecosystems are diverse and globally distributed
Surface environments with >20% salinity and subjected to periodic halite precipitation are usually dominated by haloarchaea, which is the informal name for Archaea in the class Halobacteria (McGenity and Oren, 2012)
Sequences from successfully amplified samples were clustered into operational taxonomic units (OTU) at the 97% similarity level

Summary

Introduction

Hypersaline ecosystems are diverse and globally distributed. Surface environments with >20% salinity and subjected to periodic halite precipitation are usually dominated by haloarchaea, which is the informal name for Archaea in the class Halobacteria (McGenity and Oren, 2012). Haloarchaea have a competitive advantage over many other halophiles at such high salinities, mainly because they adopt the ‘salt-in strategy’, with KCl as the primary osmolyte, as opposed to the more energetically costly biosynthesis of organic osmolytes (Oren, 2011). They have numerous other adaptations that allow them to grow in the presence of multiple other stressors such as high temperatures, UV radiation and evaporation (Jones and Baxter, 2017). Microorganisms may meet their metabolic needs by recycling organic molecules from necromass (McGenity et al, 2000; Thomas et al, 2019) or compounds leaked from other microbial cells, such as glycerol

Results

Discussion

Conclusion