Identification and plant growth-promoting activity of endophytic bacteria from sugarcane roots and genome analysis of Gluconacetobacter strain PS25

Fifty endophytic bacteria isolated from sugarcane (Saccharum officinarum L.) roots in Thailand were identified and evaluated for plant growth-promoting capability using rice as a plant model. They were identified as Gluconacetobacter (37 isolates), Pantoea (8 isolates), Burkholderia (2 isolates), and each of Nguyenibacter, Pseudomonas, and Aureimonas based on the phenotypic characteristics and 16S rRNA gene analyses. Strain PS25 has genome size of 4.4 Mbp with DNA G+C content of 64.7 mol%. The average nucleotide identity (ANIb and ANIm) values of PS25 and G. dulcium LMG1728T were 93.77% and 98.74%, respectively, and the digital DNA-DNA hybridization (dDDH) value was 88.80%. The PS25 was identified as G. dulcium. Most strains were found to fix nitrogen, solubilize P (SI=1.15-4.40) and Zn (SI=1.59-5.60), but only 9 strains could produce indole-3-acetic-acid (67.25-202.25 mu g/ml) in the medium with L-tryptophan. Furthermore, G. liquefaciens and G. dulcium were found as new strains with the ability to fix nitrogen. A. phyllosphaerae SK2, G. dulcium PS25, and G. liquefaciens LSG1 significantly increased root length (3.09-3.49 cm), shoot length (10.14-11.21 cm), number of lateral roots, and biomass of rice seedlings. This work indicates that these endophytic bacteria could be applied to enhance plant growth.