Quorum Quenching Potential of Reyranella sp. Isolated from Riverside Soil and Description of Reyranella humidisoli sp. nov.

Quorum quenching refers to any mechanism that inhibits quorum sensing processes. In this study, quorum quenching activity among bacteria inhabiting riverside soil was screened, and a novel Gram-stain-negative, rod shaped bacterial strain designated MMS21-HV4-11, which showed the highest level of quorum quenching activity, was isolated and subjected to further analysis. Strain MMS21-HV4-11 could be assigned to the genus Reyranella of Alphaproteobacteria based on the 16S rRNA gene sequence, as the strain shared 98.74% sequence similarity with Reyranella aquatilis seoho-37, and then 97.87% and 97.80% sequence similarity with Reyranella soli KIS14-15 and Reyranella massiliensis 521, respectively. The decomposed N-acyl homoserine lactone was restored at high concentrations under acidic conditions, implying that lactonase and other enzyme(s) are responsible for quorum quenching. The genome analysis indicated that strain MMS21-HV4-11 had two candidate genes for lactonase and one for acylase, and expected protein structures were confirmed. In the quorum sensing inhibition assay using a plant pathogen Pectobacterium carotovorum KACC 14888, development of soft rot was significantly inhibited by strain MMS21-HV4-11. Besides, the swarming motility by Pseudomonas aeruginosa PA14 was significantly inhibited in the presence of strain MMS21-HV4-11. Since the isolate did not display direct antibacterial activity against either of these species, the inhibition was certainly due to quorum quenching activity. In an extended study with the type strains of all known species of Reyranella, all strains were capable of degrading N-acyl homoserine lactones (AHLs), thus showing quorum quenching potential at the genus level. This is the first study on the quorum quenching potential and enzymes responsible in Reyranella. In addition, MMS21-HV4-11 could be recognized as a new species through taxonomic characterization, for which the name Reyranella humidisoli sp. nov. is proposed (type strain = MMS21-HV4-11 = KCTC 82780 = LMG 32365).