Glutamine synthetase 2 is not essential for biosynthesis of compatible solutes in Halobacillus halophilus

Abstract

Halobacillus halophilus, a moderately halophilic bacterium isolated from salt marshes, produces various compatible solutes to cope with osmotic stress. Glutamate and glutamine are dominant compatible solutes at mild salinities. Glutamine synthetase activity in cell suspensions of Halobacillus halophilus wild type was shown to be salt dependent and chloride modulated. A possible candidate to catalyze glutamine synthesis is glutamine synthetase A2, whose transcription is stimulated by chloride. To address the role of GlnA2 in the biosynthesis of the osmolytes glutamate and glutamine, a deletion mutant (ΔglnA2) was generated and characterized in detail. We compared the pool of compatible solutes and performed transcriptional analyses of the principal genes controlling the solute production in the wild type strain and the deletion mutant. These measurements did not confirm the hypothesized role of GlnA2 in the osmolyte production. Most likely the presence of another, yet to be identified enzyme has the main contribution in the measured activity in crude extracts and probably determines the total chloride-modulated profile. The role of GlnA2 remains to be elucidated.

Physiological and genomic insights into abiotic stress of halophilic archaeon Natrinema altunense 4.1R isolated from a saline ecosystem of Tunisian desert

“…In the case of the halophilic archaea H. hamelinensis, salinity levels, and glutamate concentration have been reported to trigger the change of osmotic strategies during the transition from moderate to high salinity. In halophiles generally, the uptake of compatible solutes is performed by multiple porters, such as the symporters and ABC transporters (Falb et al 2008;Saum & Müller 2007;Shiyan et al 2014). Here, we found some symporters like Na + /proline (OpuE), proton/glutamate, sodium/glutamate, and Na + /solute (Becker et al 2014;Edbeib et al 2016;Jung et al, 2012).…”

“…Trehalose can be biosynthesized by the OstAB, TreS, TreP, TreY, and TreT pathways (Avonce et al 2006). Previous studies have also reported that some halophilic cells accumulate glutamate and glutamine in high con-centrations, compatible with osmolytes (Falb et al 2008;Saum & Müller 2007;Shiyan et al 2014). The glutamate could be converted to proline by an alternative pathway in some haloarchaea strains.…”