Fungal-Lactobacteria Consortia and Enzymatic Catalysis for Polylactic Acid Production.

Polylactic acid (PLA) is the main biobased plastic manufactured on an industrial scale. This polymer is synthetized by chemical methods, and there is a strong demand for the implementation of clean technologies. This work focuses on the microbial fermentation of agro-industrial waste rich in starch for the production of lactic acid (LA) in a consolidated bioprocess, followed by the enzymatic synthesis of PLA. Lactic acid bacteria (LAB) and the fungus Rhizopus oryzae were evaluated as natural LA producers in pure cultures or in fungal-lactobacteria co-cultures formed by an LAB and a fungus selected for its metabolic capacity to degrade starch and to form consortia with LAB. Microbial interaction was analyzed by scanning electron microscopy and biofilm production was quantified. The results show that the fungus Talaromyces amestolkiae and Lactiplantibacillus plantarum M9MG6-B2 establish a cooperative relationship to exploit the sugars from polysaccharides provided as carbon sources. Addition of the quorum sensing molecule dodecanol induced LA metabolism of the consortium and resulted in improved cooperation, producing 99% of the maximum theoretical yield of LA production from glucose and 65% from starch. Finally, l-PLA oligomers (up to 19-LA units) and polymers (greater than 5 kDa) were synthetized by LA polycondensation and enzymatic ring-opening polymerization catalyzed by the non-commercial lipase OPEr, naturally produced by the fungus Ophiostoma piceae.

Enzymatic glycosylation of bioactive acceptors catalyzed by an immobilized fungal ß-xylosidase and its multi-glycoligase variant.

A recombinant ß-xylosidase (rBxTW1) from the ascomycete Talaromyces amestolkiae and a mutant derived from it, with mostly synthetic activity, have been immobilized as magnetic cross-linked enzyme aggregates (mCLEAs). The mCLEAs of rBxTW1 kept the excellent hydrolytic and O-transxylosylating activities of the free enzyme and had improved thermal and pH stability. The mCLEAs of the mutant also maintained or improved the catalytic properties of the soluble enzyme, synthetizing the O-xylosides of vanillin and (-)-epigallocatechin gallate, and the N- and S-xyloside of 3,5-dibromo-1,2,4-triazole and thiophenol, respectively. The mCLEAs were recyclable across 4 cycles of synthesis of the O-xylosides through a green and highly selective process. The magnetic properties of the scaffold used for immobilization may allow the easy recovery and reuse of the biocatalyst even from reactions containing insoluble lignocellulosic biomass.