Morphological, physiological, and biochemical characteristics
Strain GXG1230T was a Gram-positive, non-motile, aerobic strain. Cells exhibited a short rod-like morphology (Fig S5) with a length of approximately 1.5–1.8 µm and a width of 0.4–0.7 µm. The colonies of the strain GXG1230T exhibited a yellow, rounded, raised morphology, characteristics with a diameter of 1.5–2.5 mm and no diffuse pigmentation. The strain was subjected to a series of growth conditions with GXG1230T demonstrating optimal growth at 28°C. The strain demonstrated a sodium chloride tolerance concentration range of 0–10% (optimal 3.5%). The strain GXG1230T was found to be catalase positive. The strain can grow in a pH range of 6–8, with an optimal pH 7.5. Chemotaxonomic analysis revealed that strain GXG1230T exhibited the typical chemotaxonomic characteristics of members of the Microbacterium genus. The whole cell sugars contain glucose, xylose, rhamnose, galactose and malados. Lysine was identified in the peptidoglycan hydrolysate. Polar lipids are composed of diphosphatidyl glycerol, phospholipids and unidentified glycolipid (Fig S6). The methylnaphthoquinones are designated as MK-11 and MK-12. The cell fatty acids of strain GXG1230T were identified as iso-C14:0, iso-C16:0, anteiso-C15:0 and anteiso-C17:0 (Table S4), respectively. Strain GXG1230T demonstrated resistance to erythromycin and amoxicillin. In strain GXG1230T, the production of indole-3-acetic acid (IAA) was identified by the Salkowski colorimetric method. Qualitative experiments indicated that the production of IAA was evidenced by a reddening of the solution, with an approximate yield of 25.0 ± 0.6 mg/L.
Description of Microbacterium rhizophilus sp. nov
Microbacterium rhizophilus (rhi.zo’phi.lus. Gr. fem. n. rhiza, root; N.L. masc. adj. suff. - philus (from Gr. masc. adj. philos), loving; N.L. masc. adj. rhizophilus root-loving).
The strain is gram-positive, short rod, aerobic, no spore formation, with a length of approximately 1.5–1.8 µm and a width 0.4–0.7 µm. After 2–4 days of incubation at 28°C on LB medium, colonies exhibited a smooth, round, and yellow appearance. The strains can be cultivated at temperatures spanning from 4 to 40 ℃ (with an optimal range of 28 ℃) and at a pH level ranging from 6 to 8 (with an optimal pH level of 7.5). The strain is tolerant to up to 10% (w/v) NaCl (optimum 4%) in the medium. It is catalase negative. This strain shows production of indole, production of siderophores, and degradation of inorganic phosphorus. The strain utilizes D-mannose, D-ribose, maltose, lactose, D-sorbitol, D-glucose, D-galactose, and sucrose as the sole carbon source. Glycine, L-serine, L-proline, L-threonine, sarcosine, L-aspartic acid, L-tyrosine, and L-arginine as the sole nitrogen sources. The production of acid from D-xylose, D-glucose, D-galactose, esculin, D-maltose, D-saccharose, D-cellobiose, D-melezitose, D-fructose, D-turanose, and D-mannose is observed in API 50CH test strips. The API 20NE test strips converted nitrate to nitrogen and produced indole. The API ZYM test strips gave positive results for cystine arylamidase, trypsin, valine arylamidase, leucine arylamidase, naphthol-as-bi-phosphohydrolase, ipase (C8),esterase (C4), l esterase, and α-mannosidase.
The phospholipid profile includes diphosphatidyl glycerol, phospholipids and unidentified glycolipid. The whole cell sugars contain glucose, xylose, rhamnose, galactose and malados. Lysine was identified in the peptidoglycan hydrolysate. The major cellular fatty acids were iso-C14:0, iso-C16:0, anteiso-C15:0 and anteiso-C17:0. The methylnaphthoquinones were identified as MK-11 and MK-12. The genomic DNA G + C content of the type strain was determined to be 71.7 mol%.
The type strain is GXG1230T (= MCCC 1K09223T = KCTC 59252T), isolated from the rhizosphere soil of a coastal mangrove forest in Beihai city, Guangxi Zhuang Autonomous Region, China.