Surviving salt fluctuations: stress and recovery in Halobacterium salinarum, an extreme halophilic Archaeon

P Vauclare,B Franzetti,J P Kleman,F Natali,G Zaccai

doi:10.1038/s41598-020-59681-1

Abstract

Halophilic proteins subjected to below about 15% salt in vitro denature through misfolding, aggregation and/or precipitation. Halobacteria, however, have been detected in environments of fluctuating salinity such as coastal salterns and even around fresh water springs in the depths of the Dead Sea. In order to identify the underlying mechanisms of low salt survival, we explored the reactivation capacity of Halobacterium (Hbt) salinarum sub-populations after incubation in low salt media and recovery in physiological salt. Respiratory oxygen consumption was assessed in stressed cells and cell viability was estimated by Live/Dead staining and flow cytometry. In vivo neutron scattering experiments showed that the recovery of Hbt salinarum sub-populations exposed to severe low salt conditions is related to a rapid retrieval of functional molecular dynamics in the proteome. In the hypothesis that the observations on Hbt salinarum have wider relevance, they could be of key ecological significance for the dispersion of extremophiles when environmental fluctuations become severe.

Highlights

Halophilic Archaea require hypersaline conditions for optimal growth conditions found in various habitats on Earth, such as natural hypersaline lakes[1], salterns or subterranean salt deposits[2]
Dawson et al.[23] observed that halophilic archaea regulate the proportion of unsaturated diacylglycerol glycerol diethers (DGDs) in the membrane lipids according to salt fluctuations in the environment
1.5 M, growth curves exhibit a typical logarithmic biphasic killing pattern described in many bacteria exposed to harmful environmental stress[32], which may reflect an initial exponential phase corresponding to a sensitive population and a second phase with a much slower decline curve follow by a plateau

Summary

Introduction

Halophilic Archaea require hypersaline conditions (up to 5 M NaCl) for optimal growth conditions found in various habitats on Earth, such as natural hypersaline lakes[1], salterns or subterranean salt deposits[2]. The neutron scattering study revealed that, in the cytosol of reactivable cells, the necessary condition of functional molecular dynamics was rapidly restored after being significantly affected by low salt stress. With this approach, we obtained evidence that sub-populations of Hbt. salinarum can survive severe low salt conditions to start multiplying again when the salt concentration rises back to physiological values. We obtained evidence that sub-populations of Hbt. salinarum can survive severe low salt conditions to start multiplying again when the salt concentration rises back to physiological values These observations may have general ecological significance in the context of dispersion of extremophiles in fluctuating environments

Methods

Results

Conclusion