Mycoextraction: Rapid Cadmium Removal by Macrofungi-Based Technology from Alkaline Soil

Abstract

Fungi are promising materials for soil metal bioextraction and thus biomining. Here, a macrofungi-based system was designed for rapid cadmium (Cd) removal from alkaline soil. The system realized directed and rapid fruiting body development for subsequent biomass harvest. The Cd removal efficiency of the system was tested through a pot culture experiment. It was found that aging of the added Cd occurred rapidly in the alkaline soil upon application. During mushroom growth, the soil solution remained considerably alkaline, though a significant reduction in soil pH was observed in both Cd treatments. Cd and dissolved organic carbon (DOC) in soil solution generally increased over time and a significant correlation between them was detected in both Cd treatments, suggesting that the mushroom‒substratum system has an outstanding ability to mobilize Cd in an alkaline environment. Meanwhile, the growth of the mushrooms was not affected relative to the control. The estimated Cd removal efficiency of the system was up to 12.3% yearly thanks to the rapid growth of the mushroom and Cd enrichment in the removable substratum. Transcriptomic analysis showed that gene expression of the fruiting body presented considerable differences between the Cd treatments and control. Annotation of the differentially expressed genes (DEGs) indicated that cell wall sorption, intracellular binding, and vacuole storage may account for the cellular Cd accumulation. In conclusion, the macrofungi-based technology designed in this study has the potential to become a standalone biotechnology with practical value in soil heavy metal removal, and continuous optimization may make the system useful for biomining.

Cross-Kingdom Comparative Transcriptomics Reveals Conserved Genetic Modules in Response to Cadmium Stress

“…DEGs associated with cell wall remodeling may play a role in covalent Cd binding as found in this study and elsewhere ( 5 , 58 , 63 , 64 ), probably through the modification of cell wall chemistry. Besides cell wall protection, transmembrane Cd importers were found actively involved in Cd stress response.…”

“…A transcriptomic analysis of tall fescue ( Festuca arundinacea ) showed that several metal transporters, GSH, and transcriptional factors were simultaneously induced by Cd ( 50 ). In our recent study, we also found that ROS response, cell wall remodeling, metal transport, and Cys synthesis were involved in the Cd stress response in P. ostreatus ( 5 ), and glycolysis/gluconeogenesis, pentose phosphate pathway and glycine metabolism were substantially induced by Cd treatment in Purpureocillium lilacinum strain YZ1 ( 51 ). With the information above, it is possible to establish an overview of global cellular responses to Cd stress systematically.…”

“…Cadmium (Cd) is one of the most ubiquitous metallic pollutants worldwide. System-level exploration of cellular responses to Cd stress has been reported for both prokaryotic and eukaryotic organisms, while most of the exploration of cellular responses was done for specific species ( 5 – 8 ). For example, after exposure to Cd, genes encoding proteins involved in the synthesis of phenols and metallothioneins in the fungus Paxillus involutus were upregulated, resulting in the incremental production of cysteine-enriched compounds ( 9 ).…”

“…For example, after exposure to Cd, genes encoding proteins involved in the synthesis of phenols and metallothioneins in the fungus Paxillus involutus were upregulated, resulting in the incremental production of cysteine-enriched compounds ( 9 ). Pleurotus ostreatus responded to Cd stress by modulating cell processes, including cell wall remodeling, Cys-enriched compound synthesis, reactive oxygen species (ROS) response, and metal transport in a systematic manner ( 5 ). Likewise, a comparative transcriptomic study showed that a low-Cd wheat variety mobilized a wide spectrum of cellular activities such as enriched ion binding, antioxidant defense mechanisms, sulfotransferase activity, and cysteine (Cys) biosynthetic process to reduce Cd concentration ( 10 ).…”

“…Comparative genomics or transcriptomic analysis allows us to search for conserved and specific genetic elements among different species ( 12 , 13 ), especially for comparing among distantly related species ( 14 , 15 ). Several heavy metal-responding mechanisms have been identified through transcriptomic comparisons ( 5 – 8 ). For instance, based on a comparative transcriptomic study, Song et al ( 6 ) found that activation of redox homeostasis and oxidation-related metabolic processes were the primary response to Cd stress in switchgrass roots, and the hsp (heat shock protein) gene was able to improve plant tolerance against Cd significantly.…”