Identification and functional analysis of the L-ascorbate-specific enzyme II complex of the phosphotransferase system in Streptococcus mutans.

Xinyu Wu,Xinyu Wu,Wanghong Zhao,Jin Hou,Jin Hou,Xuan Chen,Xuan Chen,Xiaodan Chen,Xiaodan Chen

doi:10.1186/s12866-016-0668-9

Abstract

BackgroundStreptococcus mutans is the primary etiological agent of human dental caries. It can metabolize a wide variety of carbohydrates and produce large amounts of organic acids that cause enamel demineralization. Phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) plays an important role in carbohydrates uptake of S. mutans. The ptxA and ptxB genes in S. mutans encode putative enzyme IIA and enzyme IIB of the L-ascorbate-specific PTS. The aim of this study was to analyze the function of these proteins and understand the transcriptional regulatory mechanism.ResultsptxA−, ptxB−, as well as ptxA−, ptxB− double-deletion mutants all had more extended lag phase and lower growth yield than wild-type strain UA159 when grown in the medium using L-ascorbate as the sole carbon source. Acid production and acid killing assays showed that the absence of the ptxA and ptxB genes resulted in a reduction in the capacity for acidogenesis, and all three mutant strains did not survive an acid shock. According to biofilm and extracellular polysaccharides (EPS) formation analysis, all the mutant strains formed much less prolific biofilms with small amounts of EPS than wild-type UA159 when using L-ascorbate as the sole carbon source. Moreover, PCR analysis and quantitative real-time PCR revealed that sgaT, ptxA, ptxB, SMU.273, SMU.274 and SMU.275 appear to be parts of the same operon. The transcription levels of these genes were all elevated in the presence of L-ascorbate, and the expression of ptxA gene decreased significantly once ptxB gene was knockout.ConclusionsThe ptxA and ptxB genes are involved in the growth, aciduricity, acidogenesis, and formation of biofilms and EPS of S. mutans when L-ascorbate is the sole carbon source. In addition, the expression of ptxA is regulated by ptxB. ptxA, ptxB, and the upstream gene sgaT, the downstream genes SMU.273, SMU.274 and SMU.275 appear to be parts of the same operon, and L-ascorbate is a potential inducer of the operon.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0668-9) contains supplementary material, which is available to authorized users.

Highlights

Streptococcus mutans is the primary etiological agent of human dental caries
More than 14 unique phosphotransferase system (PTS) permeases that transport a spectrum of carbohydrates including glucose [7, 8], sucrose [9], mannose [10], sorbitol [11], fructose [12], lactose [13], galactose [14, 15], maltose [16] and nigerose [17] are present in the reference strain S. mutans UA159
The results indicate that ptxA and ptxB are involved in growth, aciduricity, acidogenesis, and formation of biofilms and extracellular polysaccharides (EPS) when S. mutans is grown with L-ascorbate as the sole carbon source

Summary

Introduction

Streptococcus mutans is the primary etiological agent of human dental caries It can metabolize a wide variety of carbohydrates and produce large amounts of organic acids that cause enamel demineralization. It can metabolize a wide variety of carbohydrates that exist in the human oral cavity and produce large amounts of organic acids via the glycolytic pathway [1]. There are examples of carbohydrates that are internalized through ATP-binding cassette transporters (ABC transporters) [2], or other pathways [3,4,5], the dominant, high-affinity, high-capacity mechanism to transport and concomitantly phosphorylate carbohydrates in S. mutans is the phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS) [6]. The study of L-ascorbate-specific PTS of S. mutans is little

Objectives

Methods

Results

Discussion

Conclusion