Ethanol and protein production from minimally processed biomass of a genetically-modified cyanobacterium over-accumulating sucrose

Abstract

One of the main bottlenecks of a microalgal or cyanobacterial biomass biorefinery is the separation of different useful fractions using simple, low energy-consuming, cost-effective, and scalable separation processes. Although the carbohydrates-rich biomass of these microorganisms presents clear advantages over conventional terrestrial crops as feedstocks for ethanol, it still requires acid and/or enzymatic hydrolysis for efficient fermentation. Here, we show the genetic modification of carbohydrates partitioning in a filamentous cyanobacterium towards the accumulation of sucrose up to 10% (w/w) as a readily fermentable feedstock. We optimized two methods for the preparation of concentrated sucrose syrups, which were efficiently converted into ethanol by yeasts, without the need of additional pretreatments. Biomass drying and milling, followed by aqueous extraction of sugars and proteins, and the recovery of proteins by short pulses of heat, kept the value of sugars as a feedstock for ethanol and protein for feed supplements within a cost-effective biomass biorefinery.

Utilization of Biomass Derived from Cyanobacteria-Based Agro-Industrial Wastewater Treatment and Raisin Residue Extract for Bioethanol Production

“…The maximum ethanol yield (EtOH/sugars % w/w) was recorded with the use of hydrolysate biomass from mixed (winery-raisin) wastewater ranged between 73.0-76.5% of the theoretical ethanol yield (Table 4). This value is higher than the 61% recorded by Kumar et al [27] who used mixed algal biomass as bioethanol substrate, and also higher than that recorded by Smachetti et al [17] (i.e., 70.2%) who applied a genetically modified strain of the cyanobacterium Anabaena. Table 4.…”

“…According to Chen et al [13], several other microalgae species contain sugars that can also be fermented to bioethanol provided that each species is appropriately pretreated according to its particular cell wall structure and carbohydrate composition. Different growth conditions and/or genetic modifications are often applied in an attempt to maximize cellular carbohydrate content [14][15][16][17]. The cost of producing biofuel from microalgae is usually higher than from conventional crops due to various factors including the high cost of chemicals used during cultivation or high-cost harvesting and drying processes [42].…”

Genetic engineering for biohydrogen production from microalgae

“…PCC 7120, and the resulting strains over-accumulated sucrose up to 10% (w/w) on a dry biomass basis under NaCl stress. 101 Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the most important enzyme for carbon fixation in photosynthetic organisms, and the rate of carbon fixation is determined by its catalytic ability 102 ; in the air, however, it has only 25% of its catalytic capacity. 100 Enhancing Rubisco activity has been shown to improve carbon fixation.…”