TABLE 3.

qrt-PCR expression ratios and function of selected envelope-related genes in S. mutans strains

CategoryGeneMean qRT-PCR fold expression ± SEa(Putative) functionDatabase or reference
UA159SMULiaFSR
Synthesis of membrane/secreted proteinsTrigger factor (ropA)1.7 ± 0.10.8 ± 0.01Ribosome-associated peptidyl-prolyl cis/trans isomerase (PPIase) foldase with chaperone and acid stress resistance functions66
ftsY2.1 ± 0.21.0 ± 0.1Membrane-associated receptor component of the signal recognition particle system responsible for targeting nascent peptides to the cell membrane20, 44
SMu17273.2 ± 0.40.7 ± 0.1OxaA-like precursor protein required for the insertion of integral membrane proteins into cell membranespFam02096 (37)
Cell wall PG biosynthesis, remodeling, and modification enzymesmurB2.4 ± 0.20.8 ± 0.03Essential UDP-N-acetylenolpyruvoylglucosamine reductase enzyme involved in the second step of the “sugar building block” necessary for PG synthesis56
dagK (dgk)3.3 ± 0.30.9 ± 0.1Diacylglycerol kinase catalyzes the formation of phophatidic acid by phosphorylating diacylglycerol; also involved in stress resistance and presumed to have C55-isoprenyl kinase activity involved in PG synthesis34, 69
SMu707c2.3 ± 0.21.3 ± 0.1Endolysin containing a β-1,4-N-acetylmuramidase domain, possibly involved in diverse cell wall functions, including PG restructuring and turnover, cell separation, and autolysis62
rgpG2.0 ± 0.10.9 ± 0.03Involved in the first step of S. mutans cell wall rhamnose-glucose polysaccharide synthesis by transferring N-acetylglucosamine-1-phosphate to a lipid carrier58, 68
Cell envelope chaperone/proteasesftsH2.5 ± 0.040.9 ± 0.1Universally conserved membrane bound metalloprotease and chaperone; in E. coli, FtsH maintains inner membrane stability by processing/degrading specific membrane proteins and transcription factors23
htrA (degP)2.9 ± 0.60.8 ± 0.003Highly conserved cell wall-associated serine protease and chaperone; S. mutans HtrA is involved in stress resistance, maturation of extracellular and surface attached proteins, biofilm formation, and genetic competence2, 16, 27
Transcriptional regulatorsSMu75310.6 ± 1.40.5 ± 0.1Hypothetical membrane protein that contains E. coli phage shock protein C (PspC) domain; E. coli PspC is a transcriptional regulator via protein-protein interactions with other phage shock proteinspFam04024 (13)
spxA (SMu2084c)6.8 ± 0.90.7 ± 0.1Conserved regulator in gram-positive bacteria that interacts with RNA polymerase haloenzyme; in B. subtilis, Spx is a regulator of the disulfide stress response to alleviate damage caused by thiol oxidation45
  • a qRT-PCR expression ratios of selected genes in mid-log-phase S. mutans UA159 parent and SMULiaFSR strains, treated for 10 min with 0.5× the MIC of bacitracin versus untreated control cells. Results were obtained from three independent experiments.