Characterization and biological activities of cyclic (1 → 3, 1 → 6)-ß-glucans from Bradyrhizobium japonicum.

OBJECTIVE: To isolate cyclic (1 â†’ 3, 1 â†’ 6)-ß-glucan from Bradyrhizobium japonicum MTCC120, to characterize its structure and to study its biological activities. RESULTS: The degree of polymerization of cyclic (1 â†’ 3, 1 â†’ 6)-ß-glucan varied between 10 and 13 and with substituents acetyl, succinyl and phosphocholine. The cyclic glucans showed bimodal particle size distribution, with hydrodynamic diameters of 1.92 and 231 nm corresponding to monomeric and aggregated cyclic glucans, respectively. SEM and TEM images showed that the glucans formed aggregates of nanorods. The glucans were biocompatible, exhibited good antioxidant activity and had the abilities to bind to Aniline Blue dye to form a fluorescence complex which was concentration dependent. CONCLUSION: The glucans isolated are cyclic and have good antioxidant activities, hence have potential application in food and pharmaceutical industries. Their dye binding ability could be exploited in medical imaging to reduce the cytotoxicity of the dyes.

Efflux pumps of Mycobacterium tuberculosis play a significant role in antituberculosis activity of potential drug candidates.

Active efflux of drugs mediated by efflux pumps that confer drug resistance is one of the mechanisms developed by bacteria to counter the adverse effects of antibiotics and chemicals. To understand these efflux mechanisms in Mycobacterium tuberculosis, we generated knockout (KO) mutants of four efflux pumps of the pathogen belonging to different classes. We measured the MICs and kill values of two different compound classes on the wild type (WT) and the efflux pump (EP) KO mutants in the presence and absence of the efflux inhibitors verapamil and l-phenylalanyl-l-arginyl-ß-naphthylamide (PAßN). Among the pumps studied, the efflux pumps belonging to the ABC (ATP-binding cassette) class, encoded by Rv1218c, and the SMR (small multidrug resistance) class, encoded by Rv3065, appear to play important roles in mediating the efflux of different chemical classes and antibiotics. Efflux pumps encoded by Rv0849 and Rv1258c also mediate the efflux of these compounds, but to a lesser extent. Increased killing is observed in WT M. tuberculosis cells by these compounds in the presence of either verapamil or PAßN. The efflux pump KO mutants were more susceptible to these compounds in the presence of efflux inhibitors. We have shown that these four efflux pumps of M. tuberculosis play a vital role in mediating efflux of different chemical scaffolds. Inhibitors of one or several of these efflux pumps could have a significant impact in the treatment of tuberculosis. The identification and characterization of Rv0849, a new efflux pump belonging to the MFS (major facilitator superfamily) class, are reported.

Process optimization and kinetic modelling of cyclic (1→3, 1→6)-ß-glucans production from Bradyrhizobium japonicum MTCC120.

Cyclic (1→3, 1→6)-ß-glucans are water soluble, biocompatible polymers with potential applications in food and pharmaceutical industries but have not yet been exploited due to their poor yield. In the present study statistical experimental design methodology was employed to improve their production. Initial screening indicated arabinose and peptone as best carbon and nitrogen source respectively, for glucan production. Arabinose and osmolyte concentrations as well as pH significantly contributed to the glucan production. Central composite design indicated a significant interaction between osmolyte concentration and pH on glucan production. The maximum amount of cyclic glucan produced was 6.7g/L in a 2.5L reactor in batch conditions. The logistic equation for cell growth and Luedeking-Piret equation for glucan production could satisfactorily simulate the batch kinetics data. Cyclic ß-glucans could efficiently encapsulate a hydrophobic molecule, curcumin and increase its solubility in water, thus indicating that these glucans have potential as drug delivery systems.