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[Objective] To explore the effects of strain CDWB36 and its metabolite pyrroloquinoline quinone (PQQ) on the drought resistance and growth of pepper, so as to provide efficient strain resources for the development and utilization of multifunctional microbial agents. [Methods] A strain CDWB36 was identified based on the morphological characteristics and the 16S rRNA gene-based phylogenetic tree. HPLC and spectroscopy were employed to detect PQQ. The fermentation conditions were optimized by single factor tests with PQQ production as the indicator. The effects of the PQQ-containing microbial agent on the growth, physio-biochemical characteristics, soil nutrients, and rhizosphere microbial community structure of pepper under drought stress were determined by pot experiments. [Results] Strain CDWB36 was identified as Acinetobacter calcoaceticus and it had the ability to produce PQQ. The optimum conditions of strain CDWB36 for producing PQQ were 10 g/L yeast powder, 4 g/L mixed nitrogen sources (ammonium sulfate: glutamic acid: tyrosine=2:1:1), 1.0 g/L MgSO4, 0.40 g/L CaCl2, 0.5% inoculum amount, 28 ℃, and pH 6.5. The PQQ production of the strain in shake flasks after 7 days of fermentation at the optimized conditions reached 61.48 mg/L, which increased by 3.3 times compared with that before optimization. Compared with CK, the PQQ-containing microbial agent increased the plant height, stem diameter, aboveground fresh weight, and belowground fresh weight of pepper by 35.05%, 8.22%, 14.41%, and 51.70%, respectively, demonstrating better plant growth-promoting effect than the PQQ solution. Moreover, the PQQ-containing microbial agent significantly improved the activities of antioxidant enzymes and the content of osmoregulatory substances (soluble sugar, soluble protein, and proline) in leaves, while increasing the soil nutrient content. The PQQ-containing microbial agent significantly changed the relative abundance of bacteria and fungi in the rhizosphere soil of pepper, increasing the relative abundance of Bacillus, Aspergillus, and Streptococcus by 1.99 times, 1.38 times, and 8.75 times, respectively, compared with CK. [Conclusion] A. calcoaceticus CDWB36 has the ability to produce PQQ. Optimizing the fermentation conditions can effectively enhance the PQQ production. The fermentation broth of CDWB36 significantly promotes pepper growth under drought stress, and PQQ is a key substance in the broth for promoting pepper growth. Therefore, the strain has broad application prospects in enhancing the stress resistance and promoting the growth of plants.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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