Recombinant Sox Enzymes from <i>Paracoccus pantotrophus</i> Degrade Hydrogen Sulfide, a Major Component of Oral Malodor

Abstract

Hydrogen sulfide (H2S) is emitted from industrial activities, and several chemotrophs possessing Sox enzymes are used for its removal. Oral malodor is a common issue in the dental field and major malodorous components are volatile sulfur compounds (VSCs), including H2S and methyl mercaptan. Paracoccus pantotrophus is an aerobic, neutrophilic facultatively autotrophic bacterium that possesses sulfur-oxidizing (Sox) enzymes in order to use sulfur compounds as an energy source. In the present study, we cloned the Sox enzymes of P. pantotrophus GB17 and evaluated their VSC-degrading activities for the prevention of oral malodor. Six genes, soxX, soxY, soxZ, soxA, soxB, and soxCD, were amplified from P. pantotrophus GB17. Each fragment was cloned into a vector for the expression of 6×His-tagged fusion proteins in Escherichia coli. Recombinant Sox (rSox) proteins were purified from whole-cell extracts of E. coli using nickel affinity chromatography. The enzyme mixture was investigated for the degradation of VSCs using gas chromatography. Each of the rSox enzymes was purified to apparent homogeneity, as confirmed by SDS-PAGE. The rSox enzyme mixture degraded H2S in dose- and time-dependent manners. All rSox enzymes were necessary for degrading H2S. The H2S-degrading activities of rSox enzymes were stable at 25–80°C, and the optimum pH was 7.0. The amount of H2S produced by periodontopathic bacteria or oral bacteria collected from human subjects decreased after an incubation with rSox enzymes. These results suggest that the combination of rSox enzymes from P. pantotrophus GB17 is useful for the prevention of oral malodor.

Characterization of the microbial community in a biotrickling filter treating a complex mixture of gaseous compounds causing odor nuisance

“…In this regard, the relative abundance of genus Paracoccus was related with the removal of NH 3 , H 2 S, TMA, and DMS; the genus Thiobacillus was related with the removal of methanol; the genera Leucobacter and Denitrobacter were related with the removal of 2,5‐dimethylpyrazine; the genera Mesorhizobium and Devosia were related exclusively with the removal of DMS. There are reports that associate these genera with the oxidation of gases: for instance, genus Paracoccus with NH 3, 67 H 2 S, 68 TMA, 69 and DMS 70 oxidation, genus Thiobacillus with methanol oxidation, 71,72 and genera Leucobacter and Denitrobacter with aromatic organic compounds like pyrazines 73,74 …”