Two Alternative Pathways for the Synthesis of the Rare Compatible Solute Mannosylglucosylglycerate inPetrotoga mobilis

Abstract

The compatible solute mannosylglucosylglycerate (MGG), recently identified in Petrotoga miotherma, also accumulates in Petrotoga mobilis in response to hyperosmotic conditions and supraoptimal growth temperatures. Two functionally connected genes encoding a glucosyl-3-phosphoglycerate synthase (GpgS) and an unknown glycosyltransferase (gene Pmob_1143), which we functionally characterized as a mannosylglucosyl-3-phosphoglycerate synthase and designated MggA, were identified in the genome of Ptg. mobilis. This enzyme used the product of GpgS, glucosyl-3-phosphoglycerate (GPG), as well as GDP-mannose to produce mannosylglucosyl-3-phosphoglycerate (MGPG), the phosphorylated precursor of MGG. The MGPG dephosphorylation was determined in cell extracts, and the native enzyme was partially purified and characterized. Surprisingly, a gene encoding a putative glucosylglycerate synthase (Ggs) was also identified in the genome of Ptg. mobilis, and an active Ggs capable of producing glucosylglycerate (GG) from ADP-glucose and D-glycerate was detected in cell extracts and the recombinant enzyme was characterized, as well. Since GG has never been identified in this organism nor was it a substrate for the MggA, we anticipated the existence of a nonphosphorylating pathway for MGG synthesis. We putatively identified the corresponding gene, whose product had some sequence homology with MggA, but it was not possible to recombinantly express a functional enzyme from Ptg. mobilis, which we named mannosylglucosylglycerate synthase (MggS). In turn, a homologous gene from Thermotoga maritima was successfully expressed, and the synthesis of MGG was confirmed from GDP-mannose and GG. Based on the measurements of the relevant enzyme activities in cell extracts and on the functional characterization of the key enzymes, we propose two alternative pathways for the synthesis of the rare compatible solute MGG in Ptg. mobilis.Thermophilic and hyperthermophilic organisms, like the vast majority of other microorganisms, accumulate compatible solutes in response to water stress imposed by salt. In fact, many of the (hyper)thermophiles known were isolated from geothermal areas venting seawater (36). However, the compatible solutes of thermophilic and hyperthermophilic prokaryotes are generally different from those of their mesophilic counterparts and some, namely, di-myo-inositol-phosphate (DIP), mannosyl-di-myo-inositol-phosphate (MDIP), diglycerol phosphate, and mannosylglyceramide, are confined to organisms that grow at extremely high temperatures (19,22,34,38). Mannosylglycerate (2-␣-D-mannosylglycerate; MG), for example, is a common compatible solute of thermophiles and hyperhermophiles (23, 27, 38) but has also been found in mesophilic organisms, such as red algae, where it was first identified (6). It should also be noted that there is a growing awareness that compatible solutes are involved in other types of stress; trehalose, for example, plays a role in osmotic stress, heat stress, desiccation, and freezing (9). Some compatible solutes of ...

A Unique Pool of Compatible Solutes on Rhodopirellula baltica, Member of the Deep-Branching Phylum Planctomycetes

“…The accumulation of MGG by R. baltica came somewhat as a surprise, since MGG has only been described in two thermophilic strains of the genus Petrotoga [8], [9] and so far was not known to have a role in osmotic adaptation in mesophilic bacteria. MGG accumulates in P. miotherma during low-level osmotic adaptation whereas in P. mobilis responds to hyperosmotic conditions and supra-optimal growth temperatures [8], [9].…”

“…MGG accumulates in P. miotherma during low-level osmotic adaptation whereas in P. mobilis responds to hyperosmotic conditions and supra-optimal growth temperatures [8], [9]. The presence of this solute in the endogenous osmolyte pool of R. baltica is interesting because this bacterium is phylogenetically distinct from these thermophilic strains.…”

“…The sugar-glycerate derivative compatible solute, mannosylglucosylglycerate (MGG) has only been found in two thermophilic organisms, Petrotoga miotherma and Petrotoga mobilis [8], [9]. In the slightly halophilic bacterium P. miotherma , MGG was reported as the principal compatible solute accumulated during sub-optimal salinities, while in Petrotoga mobilis MGG was mainly accumulated during growth at supra-optimal salinities and temperatures [8], [9].…”

“…In the slightly halophilic bacterium P. miotherma , MGG was reported as the principal compatible solute accumulated during sub-optimal salinities, while in Petrotoga mobilis MGG was mainly accumulated during growth at supra-optimal salinities and temperatures [8], [9]. Curiously, α-glutamate was the major solute used by P. miotherma for osmoprotection at supra-optimal salinity [9].…”

Mycobacterium tuberculosis Rv2419c, the missing glucosyl-3-phosphoglycerate phosphatase for the second step in methylglucose lipopolysaccharide biosynthesis

“…GPG, MPG and MGPG were synthesized as previously described41. The general phosphatase substrate p -nitrophenyl phosphate (Sigma-Aldrich) was also tested as a possible substrate for GpgP.…”