Disclosing Lactobacillus delbrueckii subsp. bulgaricus intraspecific diversity in exopolysaccharides production

Exopolysaccharides production by 3 ropy strains of Lactobacillus delbrueckii subsp. bulgaricus of dairy origin was evaluated in synthetic medium by combining different approaches: impedometric measurements, fluorescent microscopy and flow cytometry analyses. The evaluation of ΔE by impedometric measurement (E%_max-E%_40h) allowed the detection of EPS production in synthetic medium, but the differences in EPS production kinetic was highlighted by flow cytometry analysis and fluorescent microcopy. This approach enabled us to unravel the diversity in EPS synthesis and release into the laboratory medium during the growth of the strains. Our results showed that the maximum EPS production occurred after 8 h of incubation, when cells were in late exponential growth phase. Furthermore, flow cytometry analysis revealed that only part of the cell population could be identified as EPS producer or as EPS-bounded cell. Therefore, the combined approach used, allowed us to define at the same time the kinetics of EPS production and release by three strains belonging to the same species and, highlight that the production of EPS depends also on the number of EPS-producing cells within the same population. This approach could be useful for the selection of strains to be used as starter cultures in dairy products where EPS production is considered an important feature.