Extremely Halophilic Archaeal Communities Are Resilient to Short-Term Entombment in Halite. Haloarchaea in halite crystals

Some haloarchaea can avoid the harsh conditions present in evaporating brines by entombment in brine inclusions within forming halite crystals. By doing this, a subset of haloarchaea survive inside halite crystals over geological time. However, the ecological dynamics 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. Archaea were approximately 500-fold more abundant in halite compared with Bacteria. Haloarchaea were dominant, comprising >95% of the archaeal community. Unexpectedly, the diversity and composition of halite-entombed archaeal communities showed little change over the duration of the experiment. The OTU richness of the communities after 21 weeks was indistinguishable from the parent brine and overall archaeal abundance in halite did not show any clear temporal trends, suggesting that short-term survival in halite is a widely distributed trait among haloarchaea. Furthermore, the duration of entombment was less important than the parent brine from which the halite derived in determining the 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 over this period, 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.