A Coculture of Enterobacter and Comamonas Species Reduces Cadmium Accumulation in Rice

Abstract

The accumulation of cadmium (Cd) in plants is strongly impacted by soil microbes, but its mechanism remains poorly understood. Here, we report the mechanism of reduced Cd accumulation in rice by coculture of Enterobacter and Comamonas. In pot experiments, inoculation with the coculture decreased Cd content in rice grain and increased non-bioavailable Cd amount in Cd-spiked soils. Fluorescence in situ hybridization (FISH) and scanning electron microscopy (SEM) detection showed that the coculture colonized in the rhizosphere and rice roots’ vascular tissue and intercellular space. Soil metagenomics data showed that the coculture increased the abundance of sulfate reduction and biofilm formation genes and related bacterial species. Moreover, the coculture increased the content of organic matter, available nitrogen, and potassium, and increased the activities of arylsulfatase, β-galactosidase, phenoloxidase, arylamidase, urease, dehydrogenase, and peroxidase in soils. In subsequent rice transcriptomics assays, we found that the inoculation with coculture activated hypersensitive response, defense-related induction, and MAPK signaling pathway in rice. Heterologous protein expression in yeast confirmed the function of four Cd binding proteins (HIP28–1, HIP28–4, BCP2, and CID8), a Cd efflux protein (BCP1), and three Cd uptake proteins (COPT4, NRAM5, and HKT6) in rice. Succinic acid and phenylalanine were subsequently proved to inhibit rice Cd(II) uptake and activate Cd(II) efflux in rice roots. Thus, we propose a model that the coculture protects rice against Cd stress via Cd immobilization in soils and reducing Cd uptake in rice.

Alleviation of Cadmium Toxicity in Thai Rice Cultivar (PSL2) Using Biofertilizer Containing Indigenous Cadmium-Resistant Microbial Consortia

“…XL8 mitigated Cd toxicity and oxidative stress in rice seedlings via intracellular formation of Cd nanoparticles [38]. Moreover, co-inoculation of Comamonas and Enterobacter species improved rice defense response, alleviated Cd stress and reduced Cd content in rice grain via Cd immobilization in soils under a pot experiment [39]. Although soil microorganisms have been extensively used to promote plant performance and restrict soil Cd, adding microorganisms into fields together with an appropriate organic substrate is recommended to maintain their substantial activities over a long period [40].…”

Responses of soil and rhizosphere microbial communities to Cd-hyperaccumulating willows and Cd contamination

“…The high expression observed in RM-H suggests that acnB plays a crucial role in the synthesis of citrate, thereby contributing to the enhanced Cd accumulation in willows. Succinic acid is an important factor for the efficient removal of Cd and has been demonstrated to inhibit Cd uptake and activate Cd outflow in rice [ 49 ]. The high expression of the structural genes in RM-L for succinic acid synthesis aligns with this previous observation.…”

Stenotrophomonas strain CD2 reduces cadmium accumulation in Brassica rapa L.

“…Additionally, inoculation with "CD2" resulted in the downregulation of a ZIP family Zn-transporter and three blue copper proteins (BCPs) in roots (Supplementary Table S3). BCPs can bind Cd(II) or participate in Cd(II) efflux (Wang et al, 2023). Thus, it appears that inoculation with "CD2" may negatively impact the expression of Zn transporters and BCPs, resulting in reduced Cd accumulation in B. rapa.…”