Soil contamination with metals is a widespread problem posing risks to humans and ecosystems. Metal contaminated soils often hold poor microbial density and biodiversity. Among soil bacteria, rhizobia have a great agronomic and environmental significance and are major contributors to a sustainable maintenance of soil fertility. This group of microorganisms are severely affected by metals, such as cadmium (Cd), but information about metal resistance mechanisms in rhizobia is still limited. A concerted approach of the different mechanisms conferring Cd tolerance to rhizobia was conducted using two Rhizobium strains with contrasting tolerances to Cd. Results show that both strains resort to the same mechanisms (extracellular immobilization, periplasmic allocation, cytoplasmic sequestration and biotransformation of toxic products) to overcome stress, but differences in the efficiencies of some mechanisms were noticed. The ability of Rhizobium to increase glutathione in the presence of Cd emerges as a central factor in the tolerance to Cd and is as a feature to be looked for when screening or transforming microorganisms to integrate plant-microbe consortia. These could promote plant growth at contaminated sites, being more efficient for the cleanup of metals from contaminated sites and the restoration of soil quality.

金属对土壤的污染是一个普遍存在的问题，对人类和生态系统构成了风险。金属污染的土壤通常具有较差的微生物密度和生物多样性。在土壤细菌中，根瘤菌在农业和环境方面具有重要意义，并且是可持续维持土壤肥力的主要因素。这一组微生物受到镉（Cd）等金属的严重影响，但有关根瘤菌中金属抗性机制的信息仍然有限。使用两种根瘤菌对赋予Cd根瘤菌耐受性的不同机制进行了协调一致的研究对镉的耐受性相反的菌株。结果表明，两种菌株利用相同的机制（细胞外固定化，周质分配，细胞质螯合和有毒产物的生物转化）克服了压力，但注意到某些机制的效率存在差异。在Cd存在下，根瘤菌增加谷胱甘肽的能力成为对Cd耐受性的主要因素，并且是筛选或转化微生物以整合植物-微生物群落时要寻找的特征。这些可以促进受污染地点的植物生长，更有效地清除受污染地点的金属并恢复土壤质量。