Abstract:[Background] Low temperature is the main obstacle factor affecting the stable and high yield of tomato in solar-energy greenhouse in northern China. We found that Streptomyces sp. TOR3209 improved the cold tolerance of tomato plants. [Objective] To explore whether the impact of strain TOR3209 on improving resistance to cold stress of tomato plants is related to their endophytic bacterial community structure and property. [Methods] Tomato roots were inoculated with strain TOR3209 in substrate culture, and cultured under low temperature (5 ℃) and mild temperature (25 ℃) separately. Traditional culture-dependent methods were used to isolate and identify bacteria, and the effects of strain TOR3209 on the composition and structure of the root and stem bacterial community were analyzed by 16S rRNA gene amplicon sequencing technology. [Results] In this study, 69 species of endophytic bacteria belonging to 28 genera, 20 families and 4 phyla were isolated. Compared to the conditions in the control group, the Shannon index and Margalef index of the endophytic bacterial community of tomato roots and stems inoculated with strain TOR3209 were increased under low and mild temperatures. At phylum level, the relative abundance of Firmicutes was increased, while that of Proteobacteria and Bacteriodetes was decreased; at genus level, the relative abundance of Bacillus was boosted, while that of Pseudomonas and Flavobacterium was reduced; at species level, after treatment with strain TOR3209, the relative abundance of Bacillus amyloliquefaciens, Bacillus velezensis, and Bacillus aryabhattai was elevated significantly. Under both temperatures of 5 ℃ and 25 ℃, Bacillus wiedmannii, Brevibacterium frigoritolerans and Acinetobacter johnsonii were isolated from the tomato plants inoculated with strain TOR3209, and the experiment demonstrated that the three bacteria are plant-beneficial and cold-adapted, and can markedly increase the heights, leaf areas and biomasses of tomato plants; especially B. frigoritolerans treatment had the most obvious effect on the biomass. Compared with the conditions in the control group, fresh weight of root and shoot rose by 55.13% and 51.03%, respectively, and dry weight rose by 48.37% and 50.95%, respectively. The pathogenic bacteria such as Pantoea agglomerans, Pseudomonas mediterranea and Pseudomonas corrugate were not isolated. [Conclusion] Inoculation with strain TOR3209 impacted the composition and structure of the bacterial community in tomato roots and stems. The relative abundance of indigenous cold-adapted and beneficial microorganisms was increased, and the pathogenic bacteria was decreased, which improved plant cold tolerance.
