A newly isolated bacterium Comamonas sp. XL8 alleviates the toxicity of cadmium exposure in rice seedlings by accumulating cadmium

Highlights: • Comamonas sp. XL8 could biosynthesize intracellular Cd-nanoparticles (CdNPs). • Genes cadA and bmtA may contribute to Cd absorption and accumulation of XL8. • XL8 significantly alleviated the toxicity and accumulation of Cd in rice seedlings. Cadmium (Cd) is a typical heavy-metal highly accumulating in crops and drinking water, thus posing a severe health risk for human health. In this study, we firstly isolated 24 Cd-resistant bacteria from the heavy-metals contaminated soil at Daye Iron Ore, in which Comamonas sp. XL8 exhibited a high resistance and strong accumulation capacity to Cd. After absorption, Comamonas sp. XL8 could biosynthesize intracellular Cd-nanoparticles (CdNPs), which has not been reported in characteristics of Comamonas genus before. We found that the gene expressions of cadA and bmtA related to Cd transportation and binding in strain XL8 were significantly upregulated with Cd exposure, suggesting that genes cadA and bmtA may contribute to the formation of CdNPs. Of particular note, the co-inoculation of Comamonas sp. XL8 and rice seedlings (Oryzae sativa L.) significantly decreased the oxidative stress-induced by Cd accumulation and subsequently alleviated toxicity of Cd exposure. Our results reveal the biochemical process of Cd accumulation in Comamonas sp. XL8 by forming CdNPs, showing that it has great potential for effective bioremediation of environmental Cd exposure.