Isolation and identification of an endophytic Acinetobacter soli JKDY-3 from rice and its plant growth-promoting effects

Objective To identify the rice endophytic strain and analyze its plant-promoting and colonization abilities,which could enrich the rice endophytic bacteria resource library,explore high-quality endophytic bacteria resources,and provide reference for the application of rice plant-promoting bacteria.Method The streak plate method was used to isolate and purify endophytic bacteria from rice root,stem and leaf tissues.Functional media were used to determine the plant-promoting functions of endophytic bacteria,including the ability to solubilize potassium and phosphorus,produce siderophores,fix nitrogen,and secrete indoleacetic acid（IAA）.The screened strains were identified by morphological characteristics,physiological and biochemical properties and 16S rRNA sequence molecular biology method.The growth curve of the strain was determined,and different carbon and nitrogen source media were screened to optimize the culture conditions.The colonization ability of the strain was studied by determining the capacity to form biofilm and pectinase,and by conducting colonization tests.The plant-promoting effect of the strain was evaluated through seed germination and rice seedling promotion experiments.ResultThe strain JKDY-3 was isolated from rice leaves.The diameter of the yellow halo formed by potassium solubilization of the strain was 26.0 mm,the diameter of the phosphorus solubilization halo was 13.7 mm,the diameter of the siderophore-producing halo was 17.7 mm,the IAA secretion amount was 58.44 mg/L,and it had nitrogen fixation ability.Phylogenetic tree showed that strain JKDY-3 was Acinetobacter soli.The rapid growth logarithmic phase of the strain JKDY-3 occurred from 2 to 14 h,and the optimal carbon and nitrogen sources of the medium were maltose and yeast extract respectively.Strain JKDY-3 had a strong biofilm formation ability.After dissolving the biofilm,the OD_570nm value of the blank control group was 0.065,while that of the strain JKDY-3 treatment group was0.196.The strain was able to produce pectinase.Strain JKDY-3 could effectively colonize in rice roots,stems,and leaves at 7 d after inoculation,with colonization amounts of 3.75×10³,7.26×10³,and 6.76×10³ CFU/g respectively.The results of the seed germination test showed that soaking seeds with strain JKDY-3 bacterial suspension could extremely significantly improve the germination potential,vitality index and bud length after germination（P＜0.01）,and significantly improve the germination index and root length after germination（P＜0.05）,the 5 in deyes increasing by 12.29%,30.05%,28.22%,16.42% and 26.80% respectively.In the insoluble potassium environment,treating rice seedlings with strain JKDY-3 could significantly increase the dry weight of the underground per plant by 36.96%,the 5 indexes indicating that strain JKDY-3 could significantly promote the root growth of rice seedlings.Conclusion The rice endophytic strain JKDY-3 is isolated from rice leaves and identified as Acinetobacter soli.The strain has good plant-promoting functions,can effectively colonize in rice plants,and can be used for the development of microbial fertilizers.