Rapid isolation of exopolysaccharide-producing Streptococcus thermophilus based on molecular marker screening

BACKGROUND As a natural food additive, exopolysaccharide (EPS) produced by Streptococcus thermophilus can improve product viscosity and texture. The protein EpsA is a putative pathway-specific transcriptional regulator for EPS biosynthesis in S. thermophilus. RESULTS According to comparative analysis of EPS biosynthetic gene clusters, a conserved region of epsA (609 bp) was employed to design primer pair epsA-F/R as a molecular marker for the isolation of EPS-producing (EPS+) S. thermophilus. Two EPS+ S. thermophiles strains, AR333 and S-3, were band-positive, whereas Lactococcus lactis NZ9000 (non-EPS-producing, EPS-), Lactobacillus casei LC2W (EPS+) and L. plantarum AR113 (EPS+) were negative by polymerase chain reaction (PCR) amplicon bands using the epsA probe. This indicated good specificity of the epsA probe to EPS+ S. thermophilus. Moreover, based on PCR screening with the epsA probe, 23 positive strains were isolated and identified as S. thermophilus from our microbial library and natural fermented milk with 141.3-309.2 mg L-1 of EPS production, demonstrating the validity of our molecular marker screening method. CONCLUSION The designed molecular marker of epsA can rapidly screen EPS+ S. thermophilus, which has potential application in the dairy and other food industries. (c) 2021 Society of Chemical Industry.

Automated summary

The designed molecular marker epsA can be used to rapidly screen EPS+ S. thermophilus, demonstrating its potential application in the dairy and other food industries. The specificity of the epsA probe to EPS+ S. thermophilus was confirmed, and 23 positive strains were successfully identified using this molecular marker. This method shows promise for efficient screening of EPS-producing strains for industrial applications.