Role of Operon aaoSo-mutT in Antioxidant Defense in Streptococcus oligofermentans

Abstract

Previously, we have found that an insertional inactivation of aaoSo, a gene encoding L-amino acid oxidase (LAAO), causes marked repression of the growth of Streptococcus oligofermentans. Here, we found that aaoSo and mutT, a homolog of pyrophosphohydrolase gene of Escherichia coli, constituted an operon. Deletion of either gene did not impair the growth of S. oligofermentans, but double deletion of both aaoSo and mutT was lethal. Quantitative PCR showed that the transcript abundance of mutT was reduced for 13-fold in the aaoSo insertional mutant, indicating that gene polarity derived from the inactivation of aaoSo attenuated the expression of mutT. Enzymatic assays were conducted to determine the biochemical functions of LAAO and MutT of S. oligofermentans. The results indicated that LAAO functioned as an aminoacetone oxidase [47.75 nmol H2O2 (min·mg protein)–1]; and MutT showed the pyrophosphohydrolase activity, which removed mutagens such as 8-oxo-dGTP. Like paraquat, aaoSo mutations increased the expression of SOD, and addition of aminoacetone (final concentration, 5 mM) decreased the mutant’s growth by 11%, indicating that the aaoSo mutants are under ROS stress. HPLC did reveal elevated levels of cytoplasmic aminoacetone in both the deletion and insertional gene mutants of aaoSo. Electron spin resonance spectroscopy showed increased hydroxyl radicals in both types of aaoSo mutant. This demonstrated that inactivation of aaoSo caused the elevation of the prooxidant aminoacetone, resulting the cellular ROS stress. Our study indicates that the presence of both LAAO and MutT can prevent endogenous metabolites-generated ROS and mutagens. In this way, we were able to determine the role of the aaoSo-mutT operon in antioxidant defense in S. oligofermentans.

Veillonella Catalase Protects the Growth of Fusobacterium nucleatum in Microaerophilic and Streptococcus gordonii-Resident Environments

“…Oxygen molecules, which are relatively inert, can be easily converted into reactive oxygen species (ROS), such as hydrogen peroxide (H 2 O 2 ), superoxide (O 2˙Ϫ ), and hydroxyl radicals (OH˙Ϫ). The damaging effects of ROS on various biological macromolecules are known to be associated with aging, mutagenesis, and tumorigenesis (34,35). Aerobes generally use two enzymes, superoxide dismutase (SOD) and catalase, to deal with oxidative stress.…”

“…Superoxide reductase (SOR) reduces super- oxide to H 2 O 2 , and afterward, rubrerythrin can catalyze the reduction of hydrogen peroxide to water (37-40). In fact, intact H 2 O 2 is relatively harmless to cells, but Fenton reactions, which can be triggered by ferrous or copper, can result in the conversion of H 2 O 2 into hydroxyl radicals, which are extremely deleterious due to its ability to indiscriminately destroy all biological macromolecules (34,41,42). Therefore, catalase and rubrerythrin play vital roles in defense against ROS through the elimination of H 2 O 2 .…”

Complete Genome Sequence of an Oral Commensal, Streptococcus oligofermentans Strain AS 1.3089

“…S. oligofermentans not only produces large amounts of hydrogen peroxide (H 2 O 2 ), it also tolerates high concentrations of H 2 O 2 ; these characteristics enable it to outcompete the dental caries pathogen Streptococcus mutans in a two-species biofilm model (3). It has been demonstrated that S. oligofermentans possesses multiple H 2 O 2 -generating enzymes, including lactate oxidase (Lox) (3), pyruvate oxidase (4), and l -amino acid oxidase ( l -AAO) (5, 6). In particular, S. oligofermentans utilizes Lox to convert the abundant lactate produced by S. mutans into H 2 O 2 , which conversely inhibits the growth of S. mutans (3).…”

The carbon catabolite repressor CcpA mediates optimal competence development in Streptococcus oligofermentans through post‐transcriptional regulation

“…Previously, we found that inactivation of the ccpA gene in Streptococcus oligofermentans , which is a close relative of S. pneumoniae and also uses ComCDE to control competence (Tong et al , ), caused a reduction in transformation efficiency (Cai et al , ). S. oligofermentans is frequently isolated from the healthy tooth surface of humans (Tong et al , ) and it suppresses the growth of the dental caries pathogen Streptococcus mutans by producing abundant amounts of hydrogen peroxide (H 2 O 2 ) (Tong et al , ; Tong et al , ; Zhang et al , ; Liu et al , ; Zhou et al , ). In the present study, we investigated the regulatory mechanisms of CcpA on competence development in S. oligofermentans .…”