Compatible Solute Synthesis and Import by the Moderate Halophile Spiribacter salinus: Physiology and Genomics

Abstract

Members of the genus Spiribacter are found worldwide and are abundant in ecosystems possessing intermediate salinities between seawater and saturated salt concentrations. Spiribacter salinus M19-40 is the type species of this genus and its first cultivated representative. In the habitats of S. salinus M19-40, high salinity is a key determinant for growth and we therefore focused on the cellular adjustment strategy to this persistent environmental challenge. We coupled these experimental studies to the in silico mining of the genome sequence of this moderate halophile with respect to systems allowing this bacterium to control its potassium and sodium pools, and its ability to import and synthesize compatible solutes. S. salinus M19-40 produces enhanced levels of the compatible solute ectoine, both under optimal and growth-challenging salt concentrations, but the genes encoding the corresponding biosynthetic enzymes are not organized in a canonical ectABC operon. Instead, they are scrambled (ectAC; ectB) and are physically separated from each other on the S. salinus M19-40 genome. Genomes of many phylogenetically related bacteria also exhibit a non-canonical organization of the ect genes. S. salinus M19-40 also synthesizes trehalose, but this compatible solute seems to make only a minor contribution to the cytoplasmic solute pool under osmotic stress conditions. However, its cellular levels increase substantially in stationary phase cells grown under optimal salt concentrations. In silico genome mining revealed that S. salinus M19-40 possesses different types of uptake systems for compatible solutes. Among the set of compatible solutes tested in an osmostress protection growth assay, glycine betaine and arsenobetaine were the most effective. Transport studies with radiolabeled glycine betaine showed that S. salinus M19-40 increases the pool size of this osmolyte in a fashion that is sensitively tied to the prevalent salinity of the growth medium. It was amassed in salt-stressed cells in unmodified form and suppressed the synthesis of ectoine. In conclusion, the data presented here allow us to derive a genome-scale picture of the cellular adjustment strategy of a species that represents an environmentally abundant group of ecophysiologically important halophilic microorganisms.

Efficient rhizobacteria promote growth and alleviate NaCl-induced stress in the plant species Sulla carnosa

“…Several studies have tried to analyze the mechanisms by which bacteria can improve the resistance in plants. Hence, some research shows that the use of PGP bacteria can promote plant growth and enhance salt tolerance capacity by inducing synthesis of osmolytes (Siddikee et al, 2011;Chanratana et al, 2017;Karnwal, 2017;León et al, 2018). Our results revealed that after evaluation, we selected Acinetobacter sp.…”

“…1, Table 1). The possible mechanism that allows this tolerance to salt, halotolerant bacteria are able under elevated salt concentration to use microbial adaptive responses to high-osmolarity stress by the accumulation of compatible solutes either synthesis or uptake (Aslam and Ali, 2018;León et al, 2018).…”

Targeting Glycinebetaine for Abiotic Stress Tolerance in Crop Plants: Physiological Mechanism, Molecular Interaction and Signaling

“…However, the GB content steeply increased under salt stress in another halophytic species, Suaeda aegyptiaca indicating towards the stress-induced metabolic plasticity existing across plant species [88]. Leon et al [89] also reported the effectiveness of GB and arsenobetaine in ameliorating salt-induced damages in the halophile, Spiribacter salinus. The radiolabeled GB was used to study its transport, and it was observed that the GB pool was intricately associated with the presence of salt in the growth medium.…”

Role of the Extremolytes Ectoine and Hydroxyectoine as Stress Protectants and Nutrients: Genetics, Phylogenomics, Biochemistry, and Structural Analysis

“…Many representatives with re-arranged or disentangled ect biosynthetic genes live in marine ecosystems [ 199 ]. Given the re-arrangement of the canonical ect gene configuration in these bacteria, one wonders if they are capable of ectoine/5-hydroxyectoine production.…”