AUTHOR=Wen Zezhang T. , Liao Sumei , Bitoun Jacob P. , De Arpan , Jorgensen Ashton , Feng Shihai , Xu Xiaoming , Chain Patrick S. G. , Caufield Page W. , Koo Hyun , Li Yihong 

TITLE=Streptococcus mutans Displays Altered Stress Responses While Enhancing Biofilm Formation by Lactobacillus casei in Mixed-Species Consortium

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2017.00524

DOI=10.3389/fcimb.2017.00524

ISSN=2235-2988

ABSTRACT=<p>Like <italic>Streptococcus mutans</italic>, lactobacilli are commonly isolated from carious sites, although their exact role in caries development remains unclear. This study used mixed-species models to analyze biofilm formation by major groups of oral lactobacilli, including <italic>L. casei, L. fermentum, L. rhamnosus, L. salivarius</italic> ssp. <italic>salivarius</italic>, and <italic>L. gasseri</italic>. The results showed that lactobacilli did not form good biofilms when grown alone, although differences existed between different species. When grown together with <italic>S. mutans</italic>, biofilm formation by <italic>L. gasseri</italic> and <italic>L. rhamnosus</italic> was increased by 2-log (<italic>P</italic> &lt; 0.001), while biofilms by <italic>L. fermentum</italic> reduced by &gt;1-log (<italic>P</italic> &lt; 0.001). <italic>L. casei</italic> enhanced biofilm formation by ~2-log when grown with <italic>S. mutans</italic> wild-type, but no such effects were observed with <italic>S. mutans</italic> deficient of glucosyltransferase GtfB and adhesin P1. Both <italic>S. mutans</italic> and <italic>L. casei</italic> in dual-species enhanced resistance to acid killing with increases of survival rate by &gt;1-log (<italic>P</italic> &lt; 0.001), but drastically reduced the survival rates following exposure to hydrogen peroxide (<italic>P</italic> &lt; 0.001), as compared to the respective mono-species cultures. When analyzed by RNA-seq, more than 134 genes were identified in <italic>S. mutans</italic> in dual-species with <italic>L. casei</italic> as either up- or down-regulated when compared to those grown alone. The up-regulated genes include those for superoxide dismutase, NADH oxidase, and members of the mutanobactin biosynthesis cluster. Among the down-regulated genes were those for GtfB and alternative sigma factor SigX. These results further suggest that interactions between <italic>S. mutans</italic> and oral lactobacilli are species-specific and may have significant impact on cariogenic potential of the community.</p>