The genomes of three Bradyrhizobium sp. isolated from root nodules of Lupinus albescens grown in extremely poor soils display important genes for resistance to environmental stress

Abstract Lupinus albescens is a resistant cover plant that establishes symbiotic relationships with bacteria belonging to the Bradyrhizobium genus. This symbiosis helps the development of these plants in adverse environmental conditions, such as the ones found in arenized areas of Southern Brazil. This work studied three Bradyrhizobium sp. (AS23, NAS80 and NAS96) isolated from L. albescens plants that grow in extremely poor soils (arenized areas and adjacent grasslands). The genomes of these three strains were sequenced in the Ion Torrent platform using the IonXpress library preparation kit, and presented a total number of bases of 1,230,460,823 for AS23, 1,320,104,022 for NAS80, and 1,236,105,093 for NAS96. The genome comparison with closest strains Bradyrhizobium japonicum USDA6 and Bradyrhizobium diazoefficiens USDA110 showed important variable regions (with less than 80% of similarity). Genes encoding for factors for resistance/tolerance to heavy metal, flagellar motility, response to osmotic and oxidative stresses, heat shock proteins (present only in the three sequenced genomes) could be responsible for the ability of these microorganisms to survive in inhospitable environments. Knowledge about these genomes will provide a foundation for future development of an inoculant bioproduct that should optimize the recovery of degraded soils using cover crops.

摘要：白羽扇豆（Lupinus albescens）是一种抗逆覆盖植物，可与慢生根瘤菌属（Bradyrhizobium）细菌建立共生关系。该共生关系可帮助此类植物在巴西南部沙化区域等恶劣环境中完成生长发育。本研究选取3株从生长于极端贫瘠土壤（沙化区域及邻近草原）的白羽扇豆中分离得到的慢生根瘤菌属未定种（Bradyrhizobium sp.，菌株编号AS23、NAS80及NAS96）开展研究。采用离子激流测序平台（Ion Torrent）及IonXpress文库制备试剂盒对这三株菌株的基因组进行测序，结果显示AS23、NAS80、NAS96的总碱基量分别为1230460823、1320104022及1236105093。将上述菌株基因组与近缘菌株大豆慢生根瘤菌（Bradyrhizobium japonicum）USDA6以及固氮慢生根瘤菌（Bradyrhizobium diazoefficiens）USDA110进行比对，发现存在相似度低于80%的重要可变区域。仅存在于这三株测序基因组中的、编码重金属抗性/耐受因子、鞭毛运动相关因子、渗透及氧化胁迫响应因子以及热休克蛋白的基因，可能是这些微生物得以在恶劣环境中存活的关键因素。对上述基因组的研究将为未来开发接种剂生物产品奠定基础，该产品可通过覆盖作物优化退化土壤的修复效率。