Aluminum-tolerant, growth-promoting rhizosphere bacteria improve growth and alleviate aluminum stress in tea plants

Aluminum is toxic to most plants, but low concentrations of aluminum are conducive to the growth of tea plants. However, it is not clear whether aluminum treatment alters the rhizosphere microbiome of tea plants, especially growth-promoting rhizosphere bacteria. In this study, we used 16S rRNA sequencing to demonstrate that after aluminum treatment, the relative abundance of Proteobacteria in the rhizosphere bacterial community was the highest, with Burkholderia being enriched and the dominant strain. In addition, 53 strains of culturable rhizosphere bacteria, including 17 strains of Firmicutes, 23 strains of Proteobacteria, and 10 strains of Actinobacteria, were isolated and identified from the rhizosphere soil of tea plants. Further analysis of the 53 rhizosphere bacterial strains revealed that 21 strains exhibited four growth-promoting abilities. Among them, Bacillus NVLP_s (FNVLP) exhibited the maximum indole-3-acetic acid production capacity. Additionally, 51 strains could tolerate an aluminum concentration of at least 1 mol·L⁻¹, and Sinomonas gamaensis (ASG) exhibited the maximum aluminum tolerance ability, up to an aluminum concentration of 6 mmol·L⁻¹. Plant—bacteria interactions showed that ASG, FNVLP, Paraburkholderia hospita (PPH), and their synthetic community exhibited growth-promoting effects on rice roots. Furthermore, ASG, FNVLP, and PPH significantly alleviated aluminum stress in rice. Moreover, PPH and ASG promoted the growth of tea plants, especially the growth of lateral roots, irrespective of the presence of aluminum; and PPH inoculation enriched the Burkholderia community and improved carbohydrate metabolism and hormone biosynthesis and metabolism. Overall, a few bacterial strains with aluminum-tolerant and growth-promoting abilities were enriched in the rhizosphere and promoted the growth of tea plants after aluminum treatment. Thus, this study laid the foundation for further development and utilization of aluminum-tolerant, growth-promoting bacteria for the cultivation and management of tea plants.