The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain 13K301 T is MG770843. The Whole Genome Shotgun project has been deposited at DDBJ/ENA/GenBank under the accession POUC00000000. The version described in this paper is version POUC00000000.1. One supplementary figure and three supplementary tables are available with the online version of this article.

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The taxonomic positions of two Gram-negative strains, SV1470(T) and SV2184P(T), isolated from arid soil samples, were determined using a polyphasic approach. Analysis of the 16S rRNA gene and the concatenated sequences of three housekeeping gene loci (dnaK, rpoB and gyrB) confirmed that the strains belong to the genus Microvirga. Strain SV1470(T) was found to be closely related to Microvirga vignae BR3299(T) (98.8 %), Microvirga flocculans TFB(T) (98.3 %) and Microvirga lupini Lut6(T) (98.2 %), whilst similarity to other type strains of the genus ranged from 97.8 to 96.3 %; strain SV2184P(T) was found to be closely related to Microvirga aerilata 5420S-16(T) (98.0 %), Microvirga zambiensis WSM3693(T) (97.8 %) and M. flocculans ATCC BAA-817(T) (97.4 %), whilst similarity to other type strains of the genus ranged from 97.2 to 95.9 %. The G + C content of the genomic DNA was determined to be 61.5 mol % for strain SV1470(T) and 62.1 mol % for strain SV2184P(T). Both strains were found to have the same quinone system, with Q-10 as the major ubiquinone. The polar lipid profile of strain SV1470(T) was found to consist of phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, one unidentified phospholipid and one unidentified aminolipid, while that of strain SV2184P(T) consisted of phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, one unidentified aminolipid, one unidentified aminophospholipid and two unidentified phospholipids. DNA-DNA relatedness studies showed that the two strains belong to different genomic species. The strains were also distinguished using a combination of phenotypic properties. Based on the genotypic and phenotypic data, the novel species Microvirga makkahensis sp. nov. (type strain SV1470(T) = DSM 25394(T) = KCTC 23863(T) = NRRL-B 24875(T)) and Microvirga arabica sp. nov. (type strain SV2184P(T) = DSM 25393(T) = KCTC 23864(T) = NRRL-B 24874(T)) are proposed.

The taxonomic relationships and genome features of the type strains in the Streptomyces aurantiacus clade, including Streptomyces aurantiacus , Streptomyces ederensis , Streptomyces glomeroaurantiacus , Streptomyces umbrinus , Streptomyces phaeochromogenes , Streptomyces dioscori and Streptomyces tauricus , were investigated. Type strains of these species shared high 16S rRNA gene sequence similarity to each other. Multilocus sequence analysis (MLSA) based on atpD, gyrB, recA, rpoB and trpB genes revealed that S. ederensis and S. umbrinus belong to the same species. Also, S. aurantiacus and S. glomeroaurantiacus belong to the same species, but the remaining species are not closely related to each other. MLSA results were verified by the results average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) analyses; while the ANI and dDDH values between S. ederensis and S. umbrinus are 98.1 and 85.4 %, respectively, these values between S. aurantiacus and S. glomeroaurantiacus are 98.9 and 90.7 %, respectively. The presence of almost the same set of biosynthetic gene clusters and highly consistent phenotypic test results also supported the synonymy between S. ederensis and S. umbrinus , as well as between S. aurantiacus and S. glomeroaurantiacus . Therefore, S. ederensis should be reclassified as a later heterotypic synonym of S. umbrinus and S. glomeroaurantiacus should be reclassified as a later heterotypic synonym of S. aurantiacus .

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