Contribution of mechanosensitive channels to osmoadaptation and ectoine excretion in Halomonas elongata

Jasmina Vandrich,Friedhelm Pfeiffer,Gabriela Alfaro-Espinoza,Hans Jörg Kunte

doi:10.1007/s00792-020-01168-y

Abstract

For osmoadaptation the halophilic bacterium Halomonas elongata synthesizes as its main compatible solute the aspartate derivative ectoine. H. elongata does not rely entirely on synthesis but can accumulate ectoine by uptake from the surrounding environment with the help of the osmoregulated transporter TeaABC. Disruption of the TeaABC-mediated ectoine uptake creates a strain that is constantly losing ectoine to the medium. However, the efflux mechanism of ectoine in H. elongata is not yet understood. H. elongata possesses four genes encoding mechanosensitive channels all of which belong to the small conductance type (MscS). Analysis by qRT-PCR revealed a reduction in transcription of the mscS genes with increasing salinity. The response of H. elongata to hypo- and hyperosmotic shock never resulted in up-regulation but rather in down-regulation of mscS transcription. Deletion of all four mscS genes created a mutant that was unable to cope with hypoosmotic shock. However, the knockout mutant grew significantly faster than the wildtype at high salinity of 2 M NaCl, and most importantly, still exported 80% of the ectoine compared to the wildtype. We thus conclude that a yet unknown system, which is independent of mechanosensitive channels, is the major export route for ectoine in H. elongata.

Highlights

To allow for survival in high saline environments, many Bacteria and Archaea accumulate organic compounds like sugars, amino acids, and/or their derivatives to serve as osmolytes (Galinski 1995; Roberts 2005; Widderich et al 2016)
We made two attempts to search for additional, yet unannotated mechanosensitive channels. (a) We downloaded the entry for each mechanosensitive channel of Escherichia coli (Berrier et al 1996) and of Corynebacterium glutamicum (Cgl0879 mscL UniProt:Q8NS07; Cgl1270 yggB UniProt:P42531; KIQ_000100 UniProt:A0A072ZAU2) (Börngen et al 2010; Nottebrock et al 2003) for subsequent BLASTp analyses
All BLASTp results either retrieved the already annotated mechanosensitive channels or did not identify homologs. (b) We searched in InterPro for “mechanosensitive” and retrieved 16 InterPro domains related to mechanosensitive channels

Summary

Introduction

To allow for survival in high saline environments, many Bacteria and Archaea accumulate organic compounds like sugars, amino acids, and/or their derivatives to serve as osmolytes (Galinski 1995; Roberts 2005; Widderich et al 2016). These highly water-soluble molecules do not interfere with the cell’s metabolism and are, called compatible solutes (Brown 1976). The cytoplasmic membrane contains mechanosensitive channels, which act as emergency valves (Martinac 2001) These mechanosensitive channels are stretch-activated pores and open in response to an increase in membrane tension.

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