A potassium chloride to glycine betaine osmoprotectant switch in the extreme halophile Halorhodospira halophila

Abstract

halophiles for which osmoprotectant levels have been reported exclusively use either KCl or compatible solutes as their main osmoprotectants 4-6. This overarching view that has guided thinking regarding the dual nature of osmoprotection strategies has been challenged by recent experimental results 28,29 , which prompted us to perform the studies reported here. Most knowledge regarding halophilic osmoprotection strategies has been obtained through extensive studies of a very small number of organisms, particularly the Archaeon Halobacterium salinarum 17 and Salinibacter ruber (Bacteroidetes) 22,30. Therefore, we aimed to examine the osmoprotection strategy of extreme halophiles from other bacterial phyla, and selected two closely related 31 extremely halophilic purple photosynthetic Proteobacteria: Halorhodospira halophila 32 and Halorhodospira halochloris 33. While H. halochloris has been shown to utilize glycine betaine as its main osmoprotectant 34 , we found that H. halophila predominantly accumulates molar concentrations of KCl 28. This result implies a relatively recent and dramatic evolutionary change in osmoprotection strategy. Unexpectedly, we found that at lower salinity (approximately that of sea water) H. halophila retains an acidic proteome but does not accumulate cytoplasmic KCl beyond levels found in E. coli 28. This observation does not follow the expectation that acidic proteomes in halophiles require high levels of KCl to be functional. In addition, further studies revealed that many Halobacteriales are not limited to the use of KCl as their osmoprotectant but utilize organic osmoprotectants 29. Taken together, these observations imply an unexpected diversity in osmoprotection mechanisms. While most extreme halophiles are believed to dedicate their osmoprotection strategy either to the use of KCl or organic osmoprotectants, here we report the existence of an "omoprotection switch" in H. halophila, allowing this organism to switch between the KCl and organic osmoprotectant strategies depending on environmental conditions.

Draft Genome of Proteus mirabilis Serogroup O18 Elaborating Phosphocholine-Decorated O Antigen

“…Choline uptake is provided in P. mirabilis O18 by a high-affinity choline transport protein BetT. Choline gained in this way is involved in the glycine betaine biosynthesis pathway, which acts as an osmoprotectant ( Deole and Hoff, 2020 ). The other way for choline recruitment into the cell is the ChoP decoration pathway, where licABC genes products (kinase, permease, and cytidylyltransferase, respectively) incorporate, and modify choline molecule.…”

Niche breadth affects bacterial transcription patterns along a salinity gradient

“…The nonsignificant relationship of the regulation of osmoprotectant transporters against cellular stress levels was not unexpected (Table 2), at least not if stress levels of salinity ranges passing the optimum were included in the regression because within the same organism different osmoregulation mechanisms may be relevant under hypo-or hyperosmotic stress (Deole & Hoff, 2020;Lin et al, 2017).…”

Compatible Solute (Entry Type: Medium Entry)

“…Recent work indicates that some microorganisms are able to combine the salt-in and compatible solute accumulation strategies depending on the environmental conditions (Deole and Hoff 2020).…”