Biodegradation of PBAT and PHB/PBAT by Aspergillus and Purpureocillium isolates

In recent years blends and composites of biodegradable polymers have been developed as alternatives to petroleum-based plastics. Polybutylene adipate terephthalate (PBAT) and polyhydroxybutyrate (PHB) are examples of polymers that received much attention due to their interesting mechanical properties. However, although PHB presents a high biodegradation potential, PBAT is quite difficult to biodegrade under environmental conditions, and consequently only few microorganisms are known with this capability. In this work, two fungi recently isolated from soil were characterized regarding their ability to biodegrade PBAT and PHB/PBAT films. The polymers were the sole carbon and energy source, and biodegradation assays were performed in monoculture and in coculture. Biodegradation was assessed in solid and liquid media. Clear zones formation was monitored during incubation in agar plates containing the polymers, and films weight loss were measured in incubations in liquid medium. The consumption of oxygen was also monitored to confirm biodegradation.These fungi could efficiently biodegrade PHB/PBAT films at similar extents. Remarkably, after 14 days of incubation, isolate 7 (assigned to Aspergillus pseudoflectus) achieved 40.7 % (wt) biodegradation and isolate 9 (assigned to Purpureocillium lilacinum) 43.4 % (wt), whereas the coculture biodegraded 40.6 % (wt). PBAT biodegradation was far more challenging, and the fungi took 287 days to reach similar biodegradation percentages (41.2 % by isolate 9 and 30.2 % by isolate 7). This is the first study reporting the biodegradation PHB/PBAT films by aerobic mesophilic fungi. These fungi are promising candidates for the development of PBAT biodegradation technologies, and bioremediation strategies.