Structural and immunological studies of an exopolysaccharide from Acinetobacter junii BB1A.

A water-soluble heteropolysaccharide (PS) was isolated from extracellular polymeric substances (EPS) produced by a novel metal tolerant bacterium, Acinetobacter junii BB1A. Sugar analysis showed that the PS was composed of mannose, galactose and arabinose in a molar ratio of nearly 3:1:1. Structural characterization of the PS was carried out using methylation analysis, periodate oxidation, Smith degradation and 1D/2D NMR experiments. Methylation analysis revealed that the PS was consisted of 2,4-linked-mannopyranosyl, 3,4-linked-mannopyranosyl, 2-linked-galactopyranosyl, terminal mannopyranosyl and arabinopyranosyl residues in a relative proportion of nearly 1:1:1:1:1. Smith degradation of the PS showed the presence of hydrated glyceraldehyde containing disaccharide unit consisting of α-d-Manp-(1→and→4)-α-d-Manp-(1→residues where the later was directly attached to a hydrated glyceraldehyde moiety. This polysaccharide showed significant in vitro splenocyte, thymocyte, and macrophage activations with optimum dose of 100 µg/mL for macrophage and 25 µg/mL both for the splenocyte and thymocyte.

Copper susceptibility in Acinetobacter junii BB1A is related to the production of extracellular polymeric substances.

Acinetobacter junii BB1A cells, grown in different media, were differentially inhibited in the presence of the copper. The minimum inhibitory concentration of Cu(2+) was influenced by the nutrient status of the media. The production of extracellular polymeric substances (EPS) was stimulated by the copper present in the growth medium. The nature of the EPS was anionic showing non-Newtonian pseudoplastic behaviour. The thermal behaviour of the EPS was studied by differential scanning calorimetry. The EPS was amorphous in nature with a crystalline index of 0.16. Scanning electron micrographs revealed its porous structure. Cells grown in the presence of quorum sensing inhibitor (QSI: 4-Nitropyridine-N-oxide) did not produce EPS and were found to be more sensitive to Cu(2+) than cells which produced EPS in the absence of QSI. EPS production in different media in the presence and absence of Cu(2+) was determined. The production of EPS was the highest in brain heart Infusion medium and the lowest in AB minimal medium. The sorption of Cu(2+) by EPS extracted from cells grown in non-copper-complexing AB medium was demonstrated by energy dispersive X-ray spectroscopy. A pertinent functional aspect of EPS in providing protection to A. junii in copper stress condition has been revealed.

Partial characterization and flocculating behavior of an exopolysaccharide produced in nutrient-poor medium by a facultative oligotroph Klebsiella sp. PB12.

A facultative oligotrophic strain from the water sample of River Mahananda, Siliguri India was selected for its property to produce exopolysaccharide (EPS) in nutrient-poor (oligotrophic) medium. Viability assay of the strain was performed in sterile liquid LB, R2A, river water and diluted (10(-3)) LB at 30°C and pH 7 to understand oligotrophy. The selected strain was identified by 16S rRNA gene sequencing and designated as Klebsiella sp. PB12. Phylogenetic analysis showed its closest relationship with Klebsiella variicola ATCC BAA-830(T). Purification of EPS was performed by ethanol precipitation, dialysis and freeze-drying. Chemical analysis revealed that purified EPS was mainly composed of 72.32% (w/w) neutral sugar and 14.12% (w/w) uronic acids. Fourier transform infrared (FT-IR) spectroscopy indicated the presence of hydroxyl, carboxylic and methoxyl functional groups. The optimal dosages for flocculation of activated carbon suspension were 17 mg/l EPS and 4 mM CaCl(2). EPS showed flocculating rate of above 80% over a wide range of pH (pH 3-10) whereas, more than 90% rate was noted in the temperature range (10-50°C) tested in presence of CaCl(2). Moreover, EPS showed characteristic emulsifying activity with toluene (66.6%), n-hexadecane (65%), olive oil (63.3%) and kerosene (50%). The apparent molecular weight of the EPS was ~2 × 10(5) Da.