The Plant-Associated Bacterium Stenotrophomonas rhizophila Expresses a New Enzyme for the Synthesis of the Compatible Solute Glucosylglycerol

Abstract

The rhizobacterium Stenotrophomonas rhizophila accumulates the compatible solutes glucosylglycerol (GG) and trehalose under salt stress conditions. The complete gene for the GG synthesis enzyme was cloned and sequenced. This enzyme from S. rhizophila represented a novel fusion protein composed of a putative Cterminal GG-phosphate synthase domain and an N-terminal putative GG-phosphate phosphatase domain, which was named GgpPS. A similar gene was cloned from Pseudomonas sp. strain OA146. The ggpPS gene was induced after a salt shock in S. rhizophila cells. After the salt-loaded cells reached stationary phase, the ggpPS mRNA content returned to the low level characteristic of the control cells, and GG was released into the medium. The complete ggpPS gene and a truncated version devoid of the phosphatase part were obtained as recombinant proteins. Enzyme activity tests revealed the expected abilities of the full-length protein to synthesize GG and the truncated GgpPS to synthesize GG-phosphate. However, dephosphorylation of GGphosphate was detected only with the complete GgpPS protein. These enzyme activities were confirmed by complementation experiments using defined GG-defective mutants of the cyanobacterium Synechocystis sp. strain PCC 6803. Genes coding for proteins very similar to the newly identified fusion protein GgpPS for GG synthesis in S. rhizophila were found in genome sequences of related bacteria, where these genes are often linked to a gene coding for a transporter of the Mfs superfamily.

The Gene ssl3076 Encodes a Protein Mediating the Salt-Induced Expression of ggpS for the Biosynthesis of the Compatible Solute Glucosylglycerol in Synechocystis sp. Strain PCC 6803

“…Low-molecular-mass carbohydrates were extracted from frozen cell pellets with 80% ethanol (HPLC grade; Roth) and analyzed by gas chromatography (19).…”

Establishing glucosylglycerol synthesis in potato (Solanum tuberosum l. cv. Albatros) by expression of the ggpPS gene from Azotobacter vinelandii

“…GG and other low molecular mass compounds were determined by gas-liquid chromatography [25]. These substances were extracted from 100 mg plant tissue.…”

“…To establish the GG biosynthesis in potato, the gene ggpPS for GG-phosphate phosphatase and GG-phosphate synthase from Azotobacter vinelandii [25] was first cloned under the control of the constitutive CaMV 35S promoter (series Alba-AF). None of the selected transgenic plants showed obvious morphological differences in comparison to the wild type.…”

“…For the salt-induced GG synthesis these bacteria express the bi-functional protein GG-phosphate phosphatase/synthase (GgpPS) that is composed of an N-terminal phosphatase domain fused to a C-terminal synthase domain, thus this enzyme can catalyze both reactions. Moreover, the GgpPS enzymes were shown to accept ADP-glucose as well as UDP-glucose as glucosyldonors [25]. The resurrection plant Myrothamnus flabellifolia represents the only known land plant species accumulating GG under drought stress [26], while some Liliaceae synthesize it constitutively [27].…”

Potential of biosynthesized silver nanoparticles using Stenotrophomonas sp. BHU-S7 (MTCC 5978) for management of soil-borne and foliar phytopathogens

“…S. rhizophila is considered as an important plant growth promoting bacteria and found to be associated with both rhizosphere and phylloplane20. This species is differentiated from S. maltophilia on the basis of presence of glucosyl glycerol osmolyte (found only in S. rhizophila ) and hence it exhibits high degree of salt tolerance21. Previous report by Egamberdieva et al 22.…”