Pellicle of thermotolerant Acetobacter pasteurianus strains: characterization of the polysaccharides and of the induction patterns.

Acetobacter species are well known to have the ability to grow floating on the surface of the medium by producing pellicle, which consists of cells and a self-produced matrix of cell-attached polysaccharide. We previously isolated three thermotolerant strains (SL13E-2, SL13E-3, and SL13E-4) from Sri Lankan coconut vinegar and identified all these strains as Acetobacter pasteurianus. The pellicle polysaccharides of these three strains and of A. pasteurianus SKU1108, which was originally isolated from Thailand, were characterized. The monosaccharide composition of the pellicle polysaccharides of these A. pasteurianus strains was found to be varied. For example, the pellicle polysaccharide of SL13E-2 is composed of rhamnose and glucose in the ratio 1:8, and that of SL13E-4 and mesophilic A. pasteurianus NBRC3191 consists of rhamnose, glucose and xylose in the ratio 1:5:2 and 1:4:2, respectively. On the other hand, the pellicle polysaccharides of SL13E-3 and SKU1108 strains are composed of rhamnose, glucose and galactose in the ratio 2:2:1 and 1:5:2.5, respectively. The pellicle formation of thermotolerant SL13E-2, SL13E-3, and SL13E-4 was found to be significantly induced by the addition of ethanol, while poor induction was observed with SKU1108. The size and sugar composition of the polysaccharides obtained from cells induced by ethanol and by uninduced cells were the same, indicating that the number of molecules of the polysaccharides had increased but the polysaccharide molecule remained unchanged. The addition of a sugar source such as glucose, sucrose or fructose slightly induced pellicle formation in SKU1108, especially at 40°C.