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.

Abstract

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.