Enzymatic polyethylene terephthalate (PET) recycling processes are gaining interest for their low environmental impact, use of mild conditions, and specificity. Furthermore, PET hydrolase enzymes are continuously being discovered and engineered. In this work, we studied a PET hydrolase (PET2), initially characterized as an alkaline thermostable lipase. PET2 was produced in a fusion form with a 6-histidine tag in the N-terminal. The PET2 activity on aromatic terephthalate and new indole-based polyesters was evaluated using polymers in powder form. Compared with IsPETase, an enzyme derived from Ideonella sakaiensis, PET2 showed a lower PET depolymerization yield. However, interestingly, PET2 gave significantly higher polybutylene terephthalate (PBT) and polyhexylene terephthalate (PHT) depolymerization yields. A clear preference was found for aromatic indole-derived polyesters over non-aromatic ones. No activity was detected on Akestra™, an amorphous copolyester with spiroacetal structures. Docking studies suggest that a narrower and more hydrophobic active site reduces its activity on PET but favours its interaction with PBT and PHT. Understanding the enzyme preferences of polymers will contribute to their effective use to depolymerize different types of polyesters.

The brown seaweed Alaria esculenta is the second most cultivated species in Europe and it is therefore of interest to expand its application in developing food products. In this study, a lactic acid bacteria consortium (LAB consortium) consisting of three Lactiplantabacillus plantarum strains (relative abundance ~ 94%) and a minor amount of a Levilactobacillus brevis strain (relative abundance of ~ 6%) was investigated for its ability to ferment carbohydrates available in brown seaweed. The consortium demonstrated ability in fermenting glucose, mannitol, galactose, mannose, and xylose, of which glucose and mannitol were the most favored substrates; no growth was observed on fucose, mannuronic and guluronic acid. The consortium used different pathways for carbohydrate utilization and produced lactic acid as the main metabolite. In glucose fermentations, only lactic acid was produced, but use of mannitol as carbohydrate source, resulted in co-production of lactic acid, ethanol and succinate. Xylose fermentation resulted in acetate production. The consortium was also able to utilize laminari-oligosaccharides (DP 2-4), obtained after enzymatic hydrolysis of laminarin, and produced lactic acid as metabolite. The consortium could grow directly on A. esculenta, resulting in a pH decrease to 3.8 after 7 days of fermentation. Incubation of the same seaweed at corresponding conditions without inoculation resulted in spoilage of the seaweed by endogenous bacteria.