Screening among 18 novel strains of Xanthomonas campestris pv pruni

Abstract

A screening was made among 18 novel strains of Xanthomonas campestris pv pruni. Yields, viscosity and chromatographic patterns of the biopolymers synthesized in a conventional medium (PM II), were analyzed. Yields varied from 2.3 to 8.3 g l −1. Viscosities of 3% (w/v) aqueous solutions at 25, 45 and 65°C, were determined at 6, 12, 30 and 60 rpm. All biopolymers had pseudoplastic behavior. The biopolymers showed three distinct viscosity patterns when temperature increased: no variation, decrease and increase. Polymers that maintained or increased their viscosity had higher mannose concentrations. Strain 06 was chosen for further studies because it showed a higher viscosity at 6 rpm, 26,000 mPa s at 25°C and 27,000 mPa s at 65°C, and a yield of 4.0 g l −1. The influence of the concentration of biopolymer (1 and 2%) and temperature (25, 45 and 65°C) in the viscosity was also determined. A small increase in viscosity when the temperature was raised was observed at both concentrations. Finally, the influence of fermentation time (24–96 h) on yield, viscosity and chemical composition of the biopolymers, was determined. The biopolymer obtained after 24 h of fermentation showed the higher viscosity, but the highest yield was obtained at 72 h. The biopolymer produced by strain 06 after 48 h of incubation showed similar viscosity and rheological behavior to commercial xanthan.