Study on strengthened the Cd(II) adsorption based on co-culture of fungi and cyanobacteria

Cyanobacteria are effective in the remediation of heavy metal-contaminated water, but their application is limited by the high-cost of harvesting. In this study, the growth conditions of various fungi after co-cultured with cyanobacteria were compared, and the optimal fungal–cyanobacterial symbiotic system (FCSS) was selected to investigate the behaviour and mechanism of Cd(II) adsorption. Over 95 % of Synechocystis sp. PCC6803 was harvested by Aspergillus allahabdii. The FCSS adsorbed 39.10 mg/g of Cd(II), which was 22.20 % higher than the cyanobacterial single-culture system. Adsorption of Cd(II) in FCSS was rapid and monolayered. Cd was entrapped and formed irregular crystal precipitates on the surfaces of FCSS cells. Detoxification of Cd occurred through various mechanisms, with the CO, –OH, and –COOH functional groups participating in adsorption. Real-time polymerase chain reaction and transcriptome analysis revealed that reactive oxygen species generated by Cd exposure were scavenged by antioxidant enzymes such as superoxide dismutase (SOD), nicotinamide adenine dinucleotide phosphate (NADPH), catalase (CAT) and glutathione S-transferase (GST), reducing the toxic effects. CAT and GST were the initial key players in the antioxidant response to Cd exposure, followed by SOD, while NADPH levels increased steadily. The gene expression trends of CAT, GST, and major facilitator superfamily transporters aligned with the adsorption performance. These findings provide new insights into the remediation of Cd-contaminated wastewater.