Culture conditions determine the balance between two different exopolysaccharides produced by Lactobacillus pentosus LPS26

Instituto de Productos Lácteos de Asturias (IPLA-CSIC), Ctra. Infiesto s/n, 33300 -Villaviciosa, Spain.; Instituto de la Grasa (IG-CSIC). Departamento de Biotecnología de Alimentos. Apartado 1078, 41012-Sevilla, Spain

^* To whom correspondence should be addressed. Email: anarguez{at}ipla.csic.es.

	Abstract

Lactobacillus pentosus LPS26, isolated from a natural fermentation of green olives, produces a capsular polymer constituted of two exopolysaccharides: EPS A, a high M_w polysaccharide (1.9x10⁶ Da) composed of glucose and rhamnose (3:1), and EPS B, a low M_w polysaccharide (3.3x10⁴ Da), composed of glucose and mannose (3:1). Fermentation experiments in a chemically semi-defined medium with different carbon sources (glucose, fructose, mannitol and lactose) showed that all of them but fructose supported EPS A production rather than EPS B. The influence of temperature and pH was further analyzed. As temperature dropped, increased synthesis of both EPSs was detected. The control of pH especially enhanced EPS B production. Regarding this, the maximum total EPS production (514 mg l^-1) was achieved at sub-optimum growth temperature (20°C) and pH 6.0. Continuous cultures showed that EPS A, synthesized mainly at low dilution rates, is clearly dependent on the growth rate, whereas EPS B synthesis was hardly affected. EPS production was also detected in supplemented skimmed milk but no increase on the viscosity of the fermented milk was recorded. This could be linked to the high proportion of the low M_w polysaccharide produced in these conditions in contrast to that observed in culture media. Overall, this work highlights that culture conditions have a clear impact on the type and concentration of EPS produced by the strain LPS26, and consequently, they should be carefully selected for optimization and application studies. Finally, it should be noted that this is to our knowledge the first report on exopolysaccharide production by Lb. pentosus.