AUTHOR=Zhao Jiancun , Liang Yan , Zhang Susu , Xu Zhenshang 

TITLE=Effect of sugar transporter on galactose utilization in Streptococcus thermophilus

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1267237

DOI=10.3389/fmicb.2023.1267237

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p><italic>Streptococcus thermophilus</italic> is a traditional starter for dairy products. The lactose rich in milk is the main carbon source for the growth of <italic>S. thermophilus</italic>. However, the utilization of galactose by <italic>S. thermophilus</italic> is strain-specific, and many genetic factors can affect the sugar utilization phenotype of <italic>S. thermophilus</italic> strains.</p></sec><sec><title>Methods</title><p>In this study, <italic>S. thermophilus</italic> A25, which is capable of utilizing lactose and galactose, was used as the starting strain to construct lactose permease-deficient mutant <italic>S. thermophilus</italic> Δ<italic>lacS</italic>. Subsequently, the complement vectors expressing complete lactose permease of <italic>S. thermophilus</italic> and its N-terminal 1–486 amino acid residues were constructed and transformed into <italic>S. thermophilus</italic> Δ<italic>lacS</italic>, respectively. Meanwhile, complement vectors expressing lactose permease and galactose/proton symporter of Escherichia coli were also constructed.</p></sec><sec><title>Results and Discussion</title><p>Results showed that <italic>S. thermophilus</italic> Δ<italic>lacS</italic> lost the ability to utilize lactose and galactose. By measuring the growth of the recombinant strains, it was found that the strain expressing complete lactose permease of <italic>S. thermophilus</italic> recovered the growth ability in lactose and galactose medium, while the strain expressing N-terminal of lactose permease recovered the growth ability only in lactose medium. Furthermore, the transformation of <italic>S. thermophilus</italic> Δ<italic>lacS</italic> was not successful with the complement vector expressing <italic>E. coli</italic> lactose permease, while the strain expressing <italic>E. coli</italic> galactose/proton symporter could recover its growth ability in the galactose medium. These results suggest that the properties of sugar transporters play an important role in galactose utilization by <italic>S. thermophilus</italic>.</p></sec>