title: Salt stress-induced changes in the transcriptome, compatible solutes, and membrane lipids in the facultatively phototrophic bacterium Rhodobacter sphaeroides.
abstract: Responses to NaCl stress were investigated in phototrophically grown Alphaproteobacterium Rhodobacter sphaeroides by transcriptome profiling, mutational analysis, and measurements of compatible solutes and membrane phospholipids. After exposure to salt stress, genes encoding two putative glycine betaine uptake systems, proVWX and betS, were highly upregulated. Mutational analysis revealed that BetS, not ProVWX, was the primary transporter of this compatible solute. Upon the addition of salt, exogenous glycine betaine was taken up rapidly, and maximal intracellular levels were reached within minutes. In contrast, synthesis of another important compatible solute in R. sphaeroides, trehalose, increased slowly following salt stress, reaching maximal levels only after several hours. This accumulation pattern was consistent with the more gradual increase in salt-induced transcription of the trehalose biosynthesis operon otsBA. Several genes encoding putative transcription factors were highly induced by salt stress. Multiple copies of one of these factors, crpO (RSP1275), whose product is a member of the cyclic AMP receptor protein/fumarate and nitrate reduction regulator (CRP/FNR) family, improved NaCl tolerance. When crpO was provided in multicopy, expression of genes for synthesis or transport of compatible solutes was unaltered, but the membrane phospholipid composition became biased toward that found in salt-stressed cells. Collectively, this study characterized transcriptional responses to salt stress, correlated changes in transcription with compatible solute accumulation rates, identified the main glycine betaine transporter and trehalose synthase, characterized salt-induced changes in phospholipid composition, and uncovered a transcription factor associated with changes in phospholipids. These findings set the stage for deciphering the salt stress-responsive regulatory network in R. sphaeroides.
authors: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors: Minoru
authors: M
authors: Tsuzuki
authors: Oleg V
authors: OV
authors: Moskvin
authors: Masayuki
authors: M
authors: Kuribayashi
authors: Kiichi
authors: K
authors: Sato
authors: Susana
authors: S
authors: Retamal
authors: Mitsuru
authors: M
authors: Abo
authors: Jill
authors: J
authors: Zeilstra-Ryalls
authors: Mark
authors: M
authors: Gomelsky
mesh_terms: D001622:Betaine / Q000378:metabolism; D004252:DNA Mutational Analysis; D008563:Membrane Lipids / Q000378:metabolism*; D055442:Metabolome; D009997:Osmotic Pressure; D012242:Rhodobacter sphaeroides / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction; D012965:Sodium Chloride / Q000378:metabolism* / Q000633:toxicity; D013312:Stress, Physiological; D013997:Time Factors; D059467:Transcriptome; D014199:Trehalose / Q000378:metabolism
chemical_list: D008563:Membrane Lipids; D001622:Betaine; D012965:Sodium Chloride; D014199:Trehalose