School of Minerals Processing and Bioengineering, Central South University, Changsha, China; Key Laboratory of Biometallurgy, Ministry of Education, Central South University, Changsha, China.
College of Agronomy, Hunan Agricultural University, Changsha, China.
Environ Pollut. 2020 May;260:113990. doi: 10.1016/j.envpol.2020.113990. Epub 2020 Jan 23.
Cadmium (Cd) contamination in paddy soil becomes increasingly prominent in recent years, which endangers the safe production of food crops. Cd-tolerant endophytes are ideal mediators for decreasing Cd content in rice plants, but their effects on the rice endophytic microbial community and gene expression profile have not yet been well elucidated. In this study, 58 endophytic bacteria from rice seeds were isolated and characterized. Five strains of them were selected based on their potential growth-promoting traits and strong Cd tolerance that could grow well under 4 mM Cd. By 16S ribosomal RNA (rRNA) identification, these five strains were designated as Enterobacter tabaci R2-7, Pantoea agglomerans R3-3, Stenotrophomonas maltophilia R5-5, Sphingomonas sanguinis R7-3 and Enterobacter tabaci R3-2. Pot experiments in relieving Cd stress in rice plants showed that the S. maltophilia R5-5 performed the strongest potential for reducing the Cd content in root and blade by 81.33% and 77.78%, respectively. The endophytic microbial community diversity, richness and composition were significantly altered in S. maltophilia R5-5 inoculated rice plants. Reverse-transcription qPCR (RT-qPCR) showed that the expression of Cd transporters, OsNramp5 and OsHMA2, were down-regulated in S. maltophilia R5-5-innoculated rice roots. The results indicate that the inoculation of endophytic bacteria S. maltophilia R5-5 provides a reference for alleviating the heavy metal contamination in paddy fields and can be a better alternative for guaranteeing the safe production of crops. Changes in the relative abundance of Cd-resistant microorganisms and the expression of Cd transporters might be the intrinsic factors affecting cadmium content in rice.
镉（Cd）污染在近年来的稻田土壤中日益突出，危害到粮食作物的安全生产。镉耐受内生菌是降低水稻植株镉含量的理想中介，但它们对水稻内生微生物群落和基因表达谱的影响尚未得到很好的阐明。本研究从水稻种子中分离和鉴定了 58 株内生细菌。基于其潜在的促生长特性和对 4mM Cd 的强耐受能力，从这些内生细菌中选择了 5 株能够在 4mM Cd 下良好生长的菌株。通过 16S 核糖体 RNA（rRNA）鉴定，这 5 株菌分别被命名为肠杆菌 R2-7、成团泛菌 R3-3、寡养单胞菌 R5-5、血琼脂单胞菌 R7-3 和肠杆菌 R3-2。缓解水稻植株 Cd 胁迫的盆栽试验表明，寡养单胞菌 R5-5 对降低根和叶中 Cd 含量的潜力最强，分别为 81.33%和 77.78%。寡养单胞菌 R5-5 接种水稻后，内生微生物群落的多样性、丰富度和组成发生了显著变化。逆转录 qPCR（RT-qPCR）显示，寡养单胞菌 R5-5 接种水稻根中 Cd 转运蛋白 OsNramp5 和 OsHMA2 的表达下调。结果表明，接种内生细菌寡养单胞菌 R5-5 为缓解农田重金属污染提供了参考，可以更好地保障作物的安全生产。耐 Cd 微生物相对丰度的变化和 Cd 转运蛋白的表达可能是影响水稻中 Cd 含量的内在因素。
