Construction of fungi-microalgae symbiotic system and adsorption study of heavy metal ions

Harvesting and immobilization are problem in microalgae water treatment. Here, mycelial pellets (Aspergillus fumigatus) and Synechocystis sp. PCC6803 comprised a fungi-microalgae symbiotic system (FMSS) of hypha-pellet flocculant auxiliary microalgae solidification. Optical and scanning electron microscopy (SEM) revealed that green particles were attached to fungal mycelia. A 98% adsorption and immobilization efficiency of mycelium pellets to microalgae was evident. Under the condition of 108 cells/mL logarithmic phase microalgae and no fungal culture medium, the symbiotic system had higher stability and better Cd(II) adsorption efficiency (98.89%, 37.3 mg g(-1)). Meanwhile, the symbiotic system prolonged the growth cycle of microalgae in the adsorption. After Cd(II) ion stimulation, the content of total extracellular polymeric substances (EPS) in the FMSS was significantly higher than that in the control group, and the change of extracellular polysaccharide was more obvious. High performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD) showed that the monosaccharide composition of extracellular polysaccharides increased. Three dimensional excitation emission matrix (3D-EEM) spectrum analysis showed the peak intensity of protein fluorescence changed with the treatment of heavy metals. FTIR spectra showed that the functional groups (such as -OH, -CONH-) of EPS participated in the adsorption process. The findings showed that the key components of EPS, extracellular polysaccharides and extracellular proteins, played an important role in the symbiotic system to cope with the stress of heavy metal and resist the toxicity of heavy metal. The preliminary data can inform development and utilization of engineering strains and gene transformation.

Automated summary

The fungi-microalgae symbiotic system showed great potential in enhancing stability and Cd(II) adsorption efficiency of microalgae. The key components of EPS, extracellular polysaccharides, and extracellular proteins played a crucial role in coping with heavy metal stress and toxicity. This research provides valuable insights for the development and utilization of engineered strains and gene transformation.