No abstract

A total of 182 Lactobacillus strains were screened for production of extracellular polysaccharides (EPS) by a new method: growth in liquid media with high sugar concentrations. Sixty EPS-positive strains were identi®ed; 17 strains produced more than 100 mg/l soluble EPS. Sucrose was an excellent substrate for abundant EPS synthesis. The ability to produce glucans appears to be widespread in the genus Lactobacillus. The monosaccharide composition of EPS produced by Lactobacillus reuteri strain LB 121 varied with the growth conditions (solid compared to liquid medium) and the sugar substrates (sucrose or ranose) supplied in the medium. Strain LB 121 produced both a glucan and a fructan on sucrose, but only a fructan on ranose. This is the ®rst report of fructan production by a Lactobacillus species. EPS production increased with increasing sucrose concentrations and involved extracellular sucrase-type enzymes.

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The aim of the present study was to design amphiphilic oligopeptides that can self-assemble into vesicular structures. The ratio of hydrophilic to hydrophobic block length was varied, and peptides were designed to have a hydrophobic tail in which the bulkiness of the amino acid side groups increases toward the hydrophilic domain (Ac-Ala-Ala-Val-Val-Leu-Leu-Leu-Trp-Glu(2/7)-COOH). These peptides were recombinantly produced in bacteria as an alternative to solid-phase synthesis. We demonstrate with different complementary techniques (dynamic and static light scattering, tryptophan fluorescence anisotropy, and electron microscopy) that these amphiphilic peptides spontaneously form vesicles with a radius of approximately 60 nm and a low polydispersity when dispersed in aqueous solution at neutral pH. Morphology and size of the vesicles were relatively insensitive to the variations in hydrophilic block length. Exposure to acidic pH resulted in formation of visible aggregates, which could be fully reversed to vesicles upon pH neutralization. In addition, it was demonstrated that water-soluble molecules can be entrapped inside these peptide vesicles. Such peptide vesicles may find applications as biodegradable drug delivery systems with a pH-dependent release profile.