DECONSTRUCTING ALGAL BIOMASS WITH FUNGAL ENZYMES AS AN ALTERNATIVE FEEDSTOCK FOR BIOETHANOL

CONSOLO FABIANA VERONICA; BADER ARACELI; CURATTI LEONARDO; SANCHEZ RIZZA LARA

San Luis

Congreso; XIII congreso argentino de microbiología general (SAMIGE); 2018

Sociedad Argentina de Microbiología General

The most common biofuel is first generation bioethanol, which is produced from agricultural stockssuch as corn or sugarcane in the US or Brazil, respectively. Despite the great benefit associated withpartial replacement of some fossil fuel, the fact that present and future global food security is still notfully warranted poses a serious concern on the use of these feedstocks for bioenergy purposes. Asecond generation of bioethanol from plant lignocellulosic feedstocks has been more recentlyenvisioned. Regardless of clear advantages over first-generation biofuels, such as broad availabilityand low cost of the feedstock, and non-competition with food production, they face hard-to-overcomedisadvantages due to the composition and structure of the lignocellulosic biomass, requiring quiteintensive mechanical and physicochemical pretreatments, and expensive saccharifying enzymes for itsconversion into ethanol. Aquatic microalgae and cyanobacteria are increasingly considered apromising alternative to conventional crops as feedstock for food and feed, biofuels, and other highervalueproducts. This is mainly because of a much higher photosynthetic productivity (a conservativepotential of about 50-fold) and more favorable biochemical composition and structural properties thanbiomass of terrestrial crops, and independence of arable land.In this study we took advantage of the availability of a cell wall-less mutant strain CW-15 of themicroalga Chlamydomonas reinhardtii, to advance in the analysis of algal biomass deconstruction asan alternative feedstock for ethanol or other fermentation products. Strain CW-15 was cultivated atdifferent levels of N-deficiency to trigger starch accumulation. We observed that 2.5 to 5.0 mM NH4Clin the culture medium resulted in carbohydrates accumulation up to 50% (w/w) of the drybiomass weight.At the same time we performed preliminary bioprospecting assays to identified fungal strains able tohydrolyze starch and cellulose. Among others, we identified a strain of Alternaria alternata which hasbeen isolated as a contaminant of a cyanobacterial culture. Thus, we optimized induction conditions inliquid medium for the production of hydrolytic enzymes, including culture medium, initial amount ofspores, and inducers (starch or cellulose). Under these optimized conditions, the fungal spent medium,solubilized starch at 4.0 mg glu . mg de prot -1. min -1and released reducing carbohydrates (as a proxyof saccharification) at a rate of 0.4 mg glu . mg de prot -1. min -1. Importantly, these enzymepreparations deconstructed C. reinhardtii strain CW-15 biomass at a complex-carbohydratessolubilizing and hydrolytic activities of 1.0 and 0.2 mg glu . mg de prot -1. min -1. Experiments are inprogress to further optimize yields of biomass saccharification and to determine rates of deconstructedbiomass conversion into ethanol by fermentation with the yeast Saccharomyces cerevisiae.