Screening of a tobacco growth-promoting psychrotolerant Bacillus sp. strain with effects on the root exudates of tobacco seedlings

Abstract:

[Background] Crops in high-altitude areas in southwestern China often suffer from low temperature stress. Tobacco as a thermophilic plant is particularly sensitive to low temperatures. [Objective] To isolate and screen out the strains capable of promoting tobacco seedling growth at low temperatures and study the effects of the strains on the growth and root exudates of tobacco seedlings. [Methods] We used the low temperature (10 ℃) culture method to isolate the psychrotolerant bacteria from the rhizosphere soil of tobacco seedlings planted in high-altitude areas and then employed the plate culture method to screen out the tobacco growth-promoting bacteria from the isolated bacteria. The plant growth-promoting strains were identified by 16S rRNA gene sequencing, and the growth-promoting characteristics were analyzed. Non-targeted metabolomics based on LC-MS/MS was employed to investigate the effects of the strains on the root exudates of tobacco seedlings. [Results] A psychrotolerant Bacillus sp. strain, named JZC10, was isolated. It significantly promoted tobacco seedling growth at 15 ℃ but had no significant growth-promoting effect at 25 ℃. JZC10 produced proteases and indoleacetic acid (IAA) and did not solubilize phosphorus or secrete siderophores or lipases. The strain showed stronger colonizing capacity at 15 ℃ than at 25 ℃, while it did not spread along the roots at neither temperature. At 15 ℃, the inoculation of JZC10 affected the composition of root exudates of tobacco seedlings. The content of 19 root exudates were significantly different between the JZC10 group and the control. One of the upregulated root exudates, lumichrome (5 nmol/L), significantly promoted the development of leaves and lateral roots of tobacco seedlings. [Conclusion] A psychrotolerant Bacillus strain that could promote tobacco seedling growth and root development at 15 ℃ was isolated in this study. Inoculating this strain changed the root exudate composition of tobacco seedlings. The results of this study provide a theoretical basis for screening plant growth-promoting bacteria and studying their interactions with plants.