Colonization characteristics of Bacillus sp. Ya-1 and its effects on rhizosphere bacterial diversity of pepper

【Objective】To investigate the colonization characteristics of Bacillus sp. Ya-1 in rhizosphere，root and leaf of pepper and its effects on rhizosphere bacterial diversity，so as to provide reference for the control of pepper wilt disease by microecological regulation and the further development and utilization of Bacillus sp.【Method】Natural soil + vermiculite（Ns）and sterilized soil + vermiculite（Ss）matrix potted pepper were used as experimental materials. Using rifampicin labeling method，the 2 groups of matrix were inoculated with sterile water（A），inoculated with Ya-1 mutant（Ya-1- 200）fermentation broth that was resistant to 200 μg/mL rifampicin（B），inoculated with spore suspension of pepper fusarium wilt bacteria SMPLJLD-1（C），and inoculated with YA-1-200 fermentation broth + spore suspension of pepper fusarium wilt bacteria SMPLJLD-1（D）. At 0，1，2，3，7，10 and 20 d after inoculation，the colonization amounts of Ya-1 in rhizosphere，root and leaf were determined，and the colonization rule of Ya-1 was verified by absolute quantitative PCR. At the same time，the diversity and community structure difference of rhizosphere bacteria at 0，10 and 20 d after inoculation were compared and analyzed by high-throughput sequencing technology.【Result】The results of the detection of Ya-1 colonization in pepper plants and rhizosphere using rifampicin labeling method showed that after 3 d of inoculation， the colonization amount of Ya-1 in rhizosphere soil and leaves under treatments B and D gradually decreased，and tended to be stable after 20 d，and it was above the level of 1×10⁴ CFU/g after 20 d. The results of absolute quantitative PCR showed that after B and D treatment，the copy number of Ya-1 unit samples in rhizosphere，root and leaf of pepper increased first and then decreased，reached the peak after 3 d of inoculation，and stabilized above 1.0×10⁵ copies/g after 20 d. Analysis based on high throughput sequencing showed that comparing with 10 and 20 d after inoculation in Ns group， ACE index and Chao1 index in B treatment were significantly decreased（P<0.05，the same below），while the 2 indexes in C and D treatments were significantly increased. The dominant bacterial phyla with relative abundances more than 4% in the rhizosphere of pepper included Actinobacteria，Acidobacteria，Bacteroidetes，Chloroflexi，Gemmatimonadetes and Proteobacteria. At 10 d after inoculation，the relative abundance of Gemmatimonadetes in the rhizosphere soil bacterial community of pepper was the lowest（4.07%）in treatment C，while it was the highest（6.77%）in treatment B. Compared with treatment A，treatment B showed obvious enrichment of Cupriavidus，Aquicella，Trinickia，Crenobacter，Alcaligenes， Devosia，Pseudomonas，Pseudogulbenkiania，Bacillus，Rhodobacter and Vogesella at 10 and 20 d after inoculation，after 10 d of inoculation，the relative abundance of Sphingomonas was greatly higher in treatment B than in treatment A，while the relative abundances of Gp6 and Methylobacillus were significantly decreased in treatment B.【Conclusion】Ya-1 can colonize in the rhizosphere，root，and leaf of pepper，and can affect the Alpha diversity of pepper rhizosphere bacteria， increase the relative abundance of bacteria with disease resistance，growth promotion and quality improvement functions in the rhizosphere soil of pepper. It is speculated that Bacillus sp. Ya-1 has the potential for further development and application.