Efficient biodegradation of poly(butylene adipate-co-terephthalate) in mild temperature by cutinases derived from a marine fungus

Abstract

Poly(butylene adipate-co-terephthalate) (PBAT) is a polyester widely used in various fields and its waste gradually accumulates in the environment, posing ecological risks. Enzymatic hydrolysis holds great potential in the end-of-life management of PBAT, but reported enzymes need to be incubated at a high temperature (e.g. 70 °C), which is supposed to cost huge amount of energy and thereby limiting its wide industrial application. Here, we found that the marine fungus Alternaria alternata FB1 could efficiently degrade PBAT in the moderate temperature (e. g. 37 °C). Two fungal cutinases (named AaCut4 and AaCut10) were predicted to determine the degradation process by establishing a hidden Markov model of PBAT hydrolases, which were verified by an in vivo gene knockout method. The in vitro expressed AaCut10 could completely depolymerize the PBAT film in 48 h, whereas AaCut4 achieved a 63.59% breakdown in 96 h at 37 °C, and no product inhibition of either enzyme was detected. Targeting AaCut10, we accomplished to increase the yield of terephthalic acid monomer to 96.01% in 96 h at 37 °C through performing site-directed mutagenesis and supplementing Ca2+ or Mg2+ in the reaction buffer. We also found PBAT hydrolases broadly distributed in different species and environments, indicating their great potential in resolving plastics contamination. Overall, our study provides novel enzyme candidates for efficient decomposition of PBAT in mild temperature and paves a way to recover plastic wastes in a low energy consumption manner, which is important for sustainable use of PBAT waste.