促进烟草生长的耐冷芽孢杆菌的筛选及其对烟苗根系分泌物的影响

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

摘要:

【背景】我国西南高海拔地区的农作物常遭受低温胁迫，其中烟草是喜温植物，对低温尤为敏感。【目的】筛选低温条件下能促进烟苗生长的根际微生物，研究其促生特性及其对烟苗根系分泌物的影响。【方法】采集高海拔烟区烟苗根际土壤，首先用10 ℃低温培养的方法分离耐冷菌，接着用平板培养法筛选能促进烟苗生长的细菌，然后再鉴定菌株，研究促生菌的促生特性，并用非靶向代谢组学LC-MS/MS分析技术检测低温条件下所分离的促生菌对烟苗根系分泌物的影响。【结果】分离到一株耐冷芽孢杆菌JZC10，该菌在15 ℃时显著促进烟苗生长和根系发育，25 ℃时无明显促生效果。该菌产蛋白酶和吲哚乙酸(indoleacetic acid, IAA)，不能溶磷，不分泌嗜铁素和脂酶。相较于25 ℃培养条件，菌株JZC10在15 ℃条件下定殖能力更强，但都不沿根系扩散。15 ℃条件下，接种菌株JZC10会影响烟苗根系分泌物组成，有19种根系分泌物在处理组和对照组之间的含量具有显著差异，其中5 nmol/L的光色素显著促进了烟苗叶片生长和侧根发育。【结论】本研究分离到一株15 ℃低温条件下能促进烟苗生长和根系发育的耐冷芽孢杆菌，并发现接种促生菌改变了烟苗根系分泌物组成，本研究的结果有望为根际促生菌资源开发以及揭示微生物与植物根系的互作关系提供理论基础。

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.