Flocculation of Microplastics in Aqueous Solutions Using Hydrophobins

• Zachary Stevenson, Chemical Engineering, University of Delaware

• Mark Blenner, Chemical & Biomolecular Engineering, University of Delaware

The pervasive environmental challenge of plastic pollution is increasingly damaging to ecosystems worldwide. While methods to collect larger plastic waste from the environment are being employed to combat this issue, these systems are ineffective for smaller scale plastics that are left behind. Traditional microplastic recovery methods are often inefficient and costly. Here we report on one possible biological mechanism that can efficiently and inexpensively collect microplastics initially identified in the fungal species Aspergillus. Aspergillus fumigatus displayed the ability to flocculate low density polyethylene powder to its surface through hydrophobins, a type of hydrophobic surface binding protein. An additional screening of other Aspergillus strains indicated their ability to flocculate plastic as well: A. niger, A, nidulans, A. flavus, and A. terreus. On a range from 0.40 0.29 to 1.40 0.83 grams of plastic per gram dry biomass, these Aspergillus strains display an efficient flocculation ability. The hydrophobins displayed in Aspergillus are RodA through RodG. An experiment with each of these hydrophobins knocked out and a control with all of the surface proteins knocked out indicate that RodA is predominantly responsible for the flocculation mechanism. This was done through inoculation of the knockout strains into nutrient-deprived solution with 18 to 23 milligrams of LDPE. RodA was then cloned into three plasmids, pYJDN, pYJDNP, and pYD5. Future plans are to implement this DNA into Saccharomyces cerevisiae EBY100, which is known for its ability to surface display proteins. Steps beyond this include expanding this process to flocculate other prevalent microplastics such as polystyrene and polypropylene. If successfully implemented, this mechanism has potential as a scalable and efficient solution to the widespread microplastic crisis. If successfully implemented, this approach could play a vital role in mitigating microplastic pollution, contributing to the preservation and restoration of marine and terrestrial ecosystems.