Isolation and identification of a novel IAA high-producing endophytic strain KlspL18 from Oryza rufipogon

Abstract:

[Objective] To confirm the taxonomic status of the novel strain KlspL18 with high yield of indole acetic acid (IAA) isolated from the leaves of Oryza rufipogon. [Methods] KlspL18 was identified based on morphological, physiological, and biochemical characteristics, phylogenetic analysis, and whole genome sequencing. The production of IAA was determined by high performance liquid chromatography (HPLC). [Results] KlspL18 was Gram-positive, non-spore-forming, rod-shaped, and catalase-positive. It grew at 15–40 °C (optimum: 28 °C), pH 6.0–12.0 (optimum: 7.0), and in the presence of 0%–15% NaCl (optimum: 1.0%), and could use multiple carbohydrates and organic acids as carbon source. The main amino acid in the cell wall of KlspL18 was ornithine, and the dominant polysaccharides in the cell wall were galactose and mannose. The stain mainly had the polar lipids of diphosphatidyl glycerol, phosphatidyl glycerol, and two unidentified glycolipids, fatty acids of anteiso-C_15:0 (30.33%), iso-C_16:0 (31.53%), and anteiso-C_17:0 (14.32%), and naphthoquinones of MK-10 and MK-11. Phylogenetic analysis of 16S rRNA gene sequence showed the highest similarity (97.64%) to the type strain of Microbacterium proteolyticum RZ36^T. The genome of KlspL18 had the G+C content of 70.2%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) between KlspL18 and the closely related strain of Microbacterium were 83.35% and 26.4%, respectively, both below the threshold for species discrimination. HPLC analysis suggested that KlspL18 had high yield of IAA (291.7 mg/L). [Conclusion] KlspL18, a novel high-IAA-producing species of Microbacterium, was named Microbacterium dongxiang sp. nov., which is a model strain KlspL18 (=CCTCC M2022446). It has the potential of improving soil fertility and promoting plant growth in agricultural production.