| Summary: | 碩士 === 長庚大學 === 生物醫學研究所 === 100 === Oral microbes can gain advantages in the oral cavity by producing inhibitory substances against competitors. This study demonstrated that Streptococcus parasanguinis FW213 inhibits the growth of S. mutans GS5 and UA159 by producing H2O2. The majority of H2O2 is produced by pyruvate oxidase (Pox) in FW213. An enhanced H2O2 production in mutant Spa_1971_241, a mutant containing a 241-nt deletion in Spa_1971, causes self-death and extracellular DNA (eDNA) production, but the eDNA is not related to biofilm formation in FW213. Furthermore, 3 open reading frames (Spa_1056, Spa_1859 and Spa_1970) that encode putative bacteriocin-related products were identified in FW213 genome. Mutant deficient in Spa_1859, encoding a putative bacteriocin, showed a stronger inhibition phenotype against S. mutans than the wild-type FW213 and the mutant deficient in Spa_1859-1862, and it is likely that an enhanced H2O2 production is responsible for this phenotype. On the other hand, truncated Spa_1971 (encoding a transcriptional regulator), the first gene of the Spa_1971-1969 operon, led to higher H2O2 production. Spa_1971 is a S-adenosylmethionine superfamily protein characterized by a conserved CxxxCxxC motif. Its truncated form may act as a powerful oxidant. Taken together, H2O2 is the primary substance that S. parasanguinis produced to inhibit the growth of S. mutans. Whether S. parasanguinis produces a bacteriocin and the targets of the possible bacteriocin remain to be determined.
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