Definition of initial phosphorus source concentration in waste glycerol-based medium for xanthan biosynthesis

Phosphorus nutrition appears to be very important in the xanthan production, next to carbon and nitrogen. Various studies indicated that xanthan production is controlled by phosphorus concentration in cultivation medium and that phosphorus is generally added in the form of phosphate salts. This paper presents an analysis of the effect of various K₂HPO₄ concentrations (0-3.00 g/L) in waste glycerol-based medium on xanthan production using Xanthomonas strain PL 4 isolated from pepper leaves. The bioprocess success was assessed based on the values of xanthan concentration in media at the end of biosynthesis, average molecular weight of the polymer, degree of glycerol conversion into xanthan and degree of total phosphorus conversion. The obtained results show that the increase of K₂HPO₄ concentration in medium from 0 g/L to 2.50 g/L significantly contributes to the rise in xanthan amount and its molecular weight, while further increase of phosphorus source concentration has a statistically insignificant effect on the values of these parameters. The greatest bioprocess success is achieved when the concentration of K₂HPO₄ in medium was 2.50 g/L. Cultivation of producing strain on medium with optimal K₂HPO₄ concentration resulted in high production of xanthan (13.26±0.20 g/L) of good quality (3.38±0.14·10⁵ g/moL) along with a relatively high degree of phosphorus conversion (73.62±0.02%).