Isolation and characterization of high exopolysaccharide-producing Weissella confusa VP30 from young children's feces

Abstract

Background: Lactic acid bacteria (LAB) are known to have a significant ability to colonize the human intestinal tract and adhere to the surface of intestinal epithelial cells. Among the various lactic acid bacteria, exopolysaccharide (EPS) producing strains are known to provide a variety of health benefits for their hosts (e.g. anti-inflammatory, antioxidant, antitumor and stress tolerant effects). Recently, EPSs and EPS-producing lactic acid cultures have gained interest within the food industry and are playing important roles as biothickeners and texturizing agents due to their hydrocolloidal nature. In this study, 156 lactic acid bacterial strains isolated from fecal samples of healthy young children were screened and evaluated for active EPS-production capability.

Results: Among the various human origin lactic acid flora isolated, Weissella confusa VP30 showed the highest EPS productivity and its EPS producing properties were characterized under various cultural conditions in this research. To document the safety of W. confusa VP30, antibiotic resistance, hemolytic, and ammonia production properties were evaluated in addition. No significant negative results were observed. The maximum EPS production by W. confusa VP30 was 59.99 ± 0.91 g/l after 48 h of cultivation in media containing 10% sucrose, far exceeding EPS production by other bacterial strains reported elsewhere. Based on gel permeation chromatography (GPC), the molecular weight of EPS produced by W. confusa VP30 was 3.8 × 10⁶ Da. Structural analysis of the released EPS fraction by ¹³C and ¹H nuclear magnetic resonance (NMR) spectroscopy revealed that W. confusa VP30 can produce dextran with glucose units linked with 96.5% α (1 → 6) glycosidic bonds and 3.5% α (1 → 3) branches.

Conclusion: The high EPS production capability and safety of W. confusa VP30 justify food industry consideration of this cell strain for further evaluation and potential industrial use.

Keywords: Dextran; Exopolysaccharide; Lactic acid bacteria; Safety; Structure; Weissella confusa.

Fig. 1

a Scanning electron microscope images of W. confusa VP30 isolated from a fecal sample from a 5 year old boy, and b Morphological aspects of EPS production by W. confusa VP30 grown under mMRS with 10% sucrose culture for 24 h

Fig. 2

Elution profile and determination of molecular weight of W. confusa VP30 EPS by gel filtration on Thermo Dionex HPLC with Ultimate 3000 RI System. Pullulan of multiple molecular mass were used as the standard

Fig. 3

1D NMR spectrum of purified EPS from W. confusa VP30 in D2O: a ¹H NMR (600 MHz); b ¹³C NMR (150 MHz). c HSQC spectrum; d HMBC spectrum

Fig. 4

a Comprehensive lysis of red blood cells was observed with clear zones around the Listeria ivanovii subsp. ivanovii ATCC 19119 (positive control). b W. confusa VP30 growth with no blood cell lysis on the blood agar. The hemolytic activity of each strain was assessed in triplicate