Foliar spraying with a synthetic community of Bacillus increases the selenium content, quality, and contribution to phyllosphere microecology of pakchoi

Due to widespread selenium insufficiency worldwide, the human body's intake of selenium through foods has been a vital approach. Microorganisms have been widely used as a green and efficient tool for selenium biofortification of crops. However, most studies have focused on one type of PGPB, while the synergistic effects of multiple PGPBs have rarely been explored. In this study, a synthetic community was constructed by selenium absorption promotion strains, including Bacillus subtilis, Bacillus cereus, and Bacillus altitudinis, which were used instead of traditional single strain. The synthetic community was inoculated on leaves by foliar spraying under two exogenous selenomethionine treatments (10 mg L−1 and 20 mg L−1). Results showed that the synthetic community improved selenium absorption, growth, and quality of pakchoi largely. In contrast to the inoculation of Bacillus subtilis, Bacillus cereus, and Bacillus altitudinis respectively, the inoculation of the synthetic community increased the fresh weight (increased by 23.22 %, 14.55 % and 16.30 %), dry weight (increased by 13.91 %, 13.59 %, and 6.32 %) and selenium content (increased by 68.61 %, 54.37 %, and 12.46 %) in the treatments with the application of 10 mg L−1 selenium. The synthetic community inoculation enhanced the fresh weight (increased by 23.50 %, 26.35 %, and 15.63 %), dry weight (increased by 25.61 %, 20.72 %, and 15.77 %), selenium content (increased by 66.05 %, 90.20 %, and 38.90 %) in the treatments with the application of 20 mg L−1 selenium. Besides, the synthetic community also increased SPAD value, the contents of soluble protein, reducing sugar, vitamin C, and nitrogen content of pakchoi. And the nitrate content was significantly decreased. High-throughput sequencing of the 16S ribosomal RNA gene indicated that foliar spraying with synthetic community increased the relative abundance of Acinetobacter. This suggested that the composition of phyllosphere bacterial taxa was optimized by the synthetic community. This study demonstrated the potential of the synthetic community in the selenium biofortification of crops.