ADP-glucose synthesis through ADP-glucose pyrophosphorylase defines the major rate-controlling step of storage polysaccharide synthesis in both bacteria and plants. We have isolated mutant strains defective in the STA6 locus of the monocellular green alga Chlamydomonas reinhardtii that fail to accumulate starch and lack ADP-glucose pyrophosphorylase activity. We show that this locus encodes a 514-amino-acid polypeptide corresponding to a mature 50-kDa protein with homology to vascular plant ADP-glucose pyrophosphorylase small-subunit sequences. This gene segregates independently from the previously characterized STA1 locus that encodes the large 53-kDa subunit of the same heterotetramer enzyme. Because STA1 locus mutants have retained an AGPase but exhibit lower sensitivity to 3-phosphoglyceric acid activation, we suggest that the small and large subunits of the enzyme define, respectively, the catalytic and regulatory subunits of AGPase in unicellular green algae. We provide preliminary evidence that both the small-subunit mRNA abundance and enzyme activity, and therefore also starch metabolism, may be controlled by the circadian clock.

Erwinia chrysanthemi is a phytopathogenic enterobacterium causing soft rot disease in a wide range of plants. Osmoregulated periplasmic glucans (OPGs) are intrinsic components of the gram-negative bacterial envelope. We cloned the opgGH operon of E. chrysanthemi, encoding proteins involved in the glucose backbone synthesis of OPGs, by complementation of the homologous locus mdoGH of Escherichia coli. OpgG and OpgH show a high level of similarity with MdoG and MdoH, respectively, and mutations in the opgG or opgH gene abolish OPG synthesis. The opg mutants exhibit a pleiotropic phenotype, including overproduction of exopolysaccharides, reduced motility, bile salt hypersensitivity, reduced protease, cellulase, and pectate lyase production, and complete loss of virulence. Coinoculation experiments support the conclusion that OPGs present in the periplasmic space of the bacteria are necessary for growth in the plant host.Osmoregulated periplasmic glucans (OPGs) are a family of oligosaccharides found in the periplasmic space of gram-negative bacteria. Their two common features are the presence of glucose as the sole constituent sugar and their increased level in media of low osmolarity (5).Members of the family Enterobacteriaceae and related bacteria synthesize a family of linear and branched OPGs that are variously substituted. The linear backbone is constituted by glucose units joined by ␤,1-2 linkages, and the branches are made of one glucose unit linked to the main chain by a ␤,1-6 linkage. In Escherichia coli, the backbone, containing 7 to 13 glucose units, is substituted with phosphoglycerol, phosphoethanolamine, and succinyl residues (19). In Erwinia chrysanthemi, the backbone contains 5 to 12 glucose units substituted with succinyl and acetyl residues (9), and in Pseudomonas syringae, the backbone, consisting of 6 to 13 glucose units, is not substituted (38). In E. coli, the OPG backbone is synthesized by the products of the mdoGH operon located in the vicinity of pyrC, a gene involved in the biosynthesis of uracil (6). In this bacterium, the defect in OPG synthesis does not confer an easily selectable phenotype in laboratory conditions. Thus, the mdoGH locus was cloned using the linked selectable genetic marker pyrC (23).Many factors are involved in the virulence of pathogenic bacteria, and OPGs appear to be among them. In P. syringae pv. syringae, the causal agent of brown spot disease of the common bean (Phaseolus vulgaris), the hrpM mutant, obtained after transposon mutagenesis, was isolated because it failed to incite disease on the host plant and to cause the hypersensitive reaction on a non-host plant such as tobacco (29). The hrpM mutant does not synthesize OPGs, and the hrpM locus complements the OPG synthesis defect of the mdoH200::Tn10 mutant of E. coli. The amino acid sequences of HrpM and MdoH are 75.5% identical and 87.5% similar (25). More recently, a transposon insertion in a gene similar to hrpM/mdoH was isolated because it severely reduces the virulence in Pseudomonas aeruginosa PA14, an opp...

Strontium is an element of fundamental importance in biomedical science. Indeed, it has been demonstrated that Sr(2+) ions can promote bone growth and inhibit bone resorption. Thus, the oral administration of Sr-containing medications has been used clinically to prevent osteoporosis, and Sr-containing biomaterials have been developed for implant and tissue engineering applications. The bioavailability of strontium metal cations in the body and their kinetics of release from materials will depend on their local environment. It is thus crucial to be able to characterize, in detail, strontium environments in disordered phases such as bioactive glasses, to understand their structure and rationalize their properties. In this paper, we demonstrate that (87)Sr NMR spectroscopy can serve as a valuable tool of investigation. First, the implementation of high-sensitivity (87)Sr solid-state NMR experiments is presented using (87)Sr-labeled strontium malonate (with DFS (double field sweep), QCPMG (quadrupolar Carr-Purcell-Meiboom-Gill), and WURST (wideband, uniform rate, and smooth truncation) excitation). Then, it is shown that GIPAW DFT (gauge including projector augmented wave density functional theory) calculations can accurately compute (87)Sr NMR parameters. Last and most importantly, (87)Sr NMR is used for the study of a (Ca,Sr)-silicate bioactive glass of limited Sr content (only ~9 wt %). The spectrum is interpreted using structural models of the glass, which are generated through molecular dynamics (MD) simulations and relaxed by DFT, before performing GIPAW calculations of (87)Sr NMR parameters. Finally, changes in the (87)Sr NMR spectrum after immersion of the glass in simulated body fluid (SBF) are reported and discussed.