Isoptericola rhizosphaerae sp. nov. and Isoptericola aurantiacus sp. nov. two novel bacteria isolated from rhizosphere soil

Two actinobacterial strains, designated GXG3202^T and GXG9306^T, were isolated from the rhizosphere soil of mangrove forests in Beihai, Guangxi Zhuang Autonomous Region, China. Phylogenetic analysis of the 16S rRNA gene sequence revealed that both strains clustered in distinct subclades in the genus Isoptericola, sharing high sequence similarity with Isoptericola halotolerans YIM 70177^T (97.9–98.8%) and Isoptericola chiayiensis 06182M-1^T (98.4–98.6%). Chemotaxonomic analysis indicated that the predominant fatty acids are anteiso-C_15:0, C_16:0, and anteiso-C_17:0. The peptidoglycan hydrolysate contained aspartate, with the menaquinone MK-9 identified as the major respiratory quinone. Polar lipid analysis identified DPG, PGL, PI, and GL as core components in both strains, with GXG3202^T uniquely containing PL1-PL2 and PG, whereas GXG9306^T lacked PL2 and PG. The genomic DNA G + C content of GXG3202^T and GXG9306^T were determined to be 72.4% and 73.1%, respectively. Digital DNA-DNA hybridization (dDDH) values between the novel strains and their closely related species ranged from 36.4%-53.1%, while average nucleotide identity (ANI) and amino acid identity (AAI) values were 80.6–83.6% and 78.7–83.8%, respectively. Our collective taxonomic evidence supports the classification of these strains as two novel species within the genus Isoptericola, for which the names Isoptericola rhizosphaerae sp. nov.(type strain GXG3202^T = MCCC 1K09564^T = KCTC 59469^T) and Isoptericola aurantiacus sp. nov. (type strain GXG9306^T = MCCC 1K09565^T = KCTC59470^T) are proposed, respectively.