Brevibacillus humidisoli sp. nov., a moderately thermoalkaliphilic and halotolerant species isolated from riverside soil

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-HV4-11T, which showed the highest level of quorum quenching activity, was isolated and subjected to further analysis. Strain MMS21-HV4-11T 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-37T, and then 97.87% and 97.80% sequence similarity with Reyranella soli KIS14-15T and Reyranella massiliensis 521T, 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-HV4-11T 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-HV4-11T. Besides, the swarming motility by Pseudomonas aeruginosa PA14 was significantly inhibited in the presence of strain MMS21-HV4-11T. 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-HV4-11T 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 T = KCTC 82780 T = LMG 32365T).

Brevibacillus ruminantium sp. nov., isolated from cow faeces

An aerobic, Gram-stain-positive, rod-shaped, endospore-forming bacterial strain, designated BB3-R1T, was isolated from cow faeces sampled in Daejeon, Republic of Korea. Growth was observed at 25-45 °C (optimum, 35-40 °C) and pH 7.0-9.0 (optimum, pH 8.0), with up to 3 % (w/v) NaCl (optimum, 0 % NaCl). blast analysis of 16S rRNA gene sequences revealed the highest sequence similarity of strain BB3-R1T to Brevibacillus borstelensis NRRL NRS-818T (98.8 %) followed by Brevibacillus panacihumi JCM 15085T (97.5 %). According to 16S rRNA gene and whole-genome based phylogenetic trees, strain BB3-R1T clustered with Brevibacillus composti FJAT-54423T and B. borstelensis NRRL NRS-818T. OrthoANI and dDDH values of strain BB3-R1T with the closely related strains were lower than 77.5 and 26.8 %, respectively. The major menaquinones and polar lipids of the strain were MK-7 and phosphatidylmonomethylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine, respectively. The major fatty acids (>10 %) were C14 : 0 iso, C15 : 0 iso, C15 : 0 anteiso and C16 : 1  ω7c alcohol. The cell-wall peptidoglycan contained cross-linked meso-diaminopimelic acid (type A1 gamma). The phenotypic, chemotaxonomic and genotypic data obtained in this study showed that the strain represents a novel species of the genus Brevibacillus, for which the name Brevibacillus ruminantium sp. nov. (type strain BB3-R1T=KACC 22663T=NBRC 115962T) is proposed.

Description of Microcella humidisoli sp. nov. and Microcella daejeonensis sp. nov., isolated from riverside soil, reclassification of Marinisubtilis pacificus as Microcella pacifica comb. nov., and emended description of the genus Microcella

Three Gram-positive, aerobic and rod shaped actinobacteria, designated strains MMS21-STM10T, MMS21-STM12T and MMS21-STM26, were isolated from riverside soil and subjected to polyphasic taxonomic analysis. The strains grew optimally at mesophilic temperatures (25-30 °C) and neutral to slightly alkaline pH (7-8), and NaCl was not required for growth. Best growth was observed on nutrient agar or marine agar media. The strains contained diphosphatidylglycerol, phosphatidylglycerol and a series of unidentified phospholipids, glycolipids and aminolipids, and anteiso-C15 : 0 and iso-C16 : 0 as the main fatty acids in common. The genome sizes ranged between 2.65 and 2.78 Mbp, and the DNA G+C contents between 70.4 and 72.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MMS21-STM10T showed highest sequence similarity of 98.3 % to Microcella putealis CV-2T, and MMS21-STM12T and MMS21-STM26 of 99.2-99.3 % to Microcella flavibacter WY83T, respectively. In the whole genome-based comparison using the orthologous average nucleotide identity and digital DNA-DNA hybridization, each of strains MMS21-STM10T and MMS21-STM12T could be separated from other species of Microcella. The genome analysis also indicated that both strains contained gene clusters involved in the biosynthesis of alkylresorcinol, microansamycin and carotenoids. The phenotypic characteristics again differentiated the strains from related species, and two new species of Microcella, Microcella humidisoli sp. nov. (type strain, MMS21-STM10T=KCTC 49773T=LMG 32522T) and Microcella daejeonensis sp. nov. (type strain, MMS21-STM12T=KCTC 49750T=LMG 32523T) are proposed accordingly. It was also evident that Marinisubtilis pacificus KN1116T should be reclassified as a new species of Microcella, and Microcella pacifica comb. nov. (type strain, KN1116T=CGMCC 1.17143T=KCTC 49299T) is proposed. In addition, an emended description of Microcella is proposed based on this study.