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

Abstract

Two actinobacterial strains, designated GXG3202^T and GXG9306^T, were isolated from the rhizosphere soil of Avicennia marina 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 (98.8% and 97.9%) and Isoptericola chiayiensis 06182M-1^T (98.4% and 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 lysine and aspartate, with the menaquinone MK-9(H₂) and MK-9(H₄) 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 two PLs and PG, whereas GXG9306^T contained one PL. 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 species of genus Isoptericola ranged from 22.2 to 44.1%, while average nucleotide identity (ANI) and amino acid identity (AAI) values were 71.0–83.6% and 74.3–83.8%, 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.