Direct consolidated bioprocessing for D-glucaric acid production from lignocellulose under subcritical water pretreatment

D-glucaric acid production from lignocellulose is a valuable research field, but meets the same challenge as other biorefinery processes that prevents it from commercialization, high production costs. The very path to tackle this is to increase the titer, rate and yield (TRY) of D-glucaric acid production and simplify the process, on which this study focused. Herein we used a novel, clean and environmentally friendly pretreatment, subcritical water pretreatment (SCWP), based on which we compared consolidated bioprocessing (CBP) by the microbial con-sortium composed of Trichoderma reesei C10 and Saccharomyces cerevisiae LGA-1C3S2 with separated hydrolysis and fermentation (SHF). CBP was found to be advantageous over SHF because of its comparable yield, much more simplified bioprocess and bigger space for cost reduction. Then CBP was upgraded to direct consolidated bioprocessing (dCBP) by adapting the microbial consortium in the raw liquors of SCWP containing inhibitors and toxic chemicals. As a result, more integrated biorefinery processes from corn stover (CS), wheat straw (WS), rice straw (RS) and switchgrass (SG) to D-glucaric acid under SCWP were developed and scaled up from shake flasks to 10 L fermenters, stirred and airlift. The TRYs of D-glucaric acid were improved significantly. The airlift fermenter was preferable for the dCBPs, producing the highest concentrations of D-glucaric acid, which were 10.03 g/L from subcritical water pretreated CS (SWCPCS), 9.53 g/L from SWCPWS, 8.87 g/L from SWCPRS and 10.66 g/L from SWCPSG respectively. Subsequently, the dCBPs were coupled with the downstream separation to establish a closed-circuit circulation and 30 rounds was run successfully. The highly integrated process from lignocellulose to D-glucaric acid with the smallest number of single unit operations was obtained and reported for the first time, providing an important design for biorefinery. This work is of great significance for bio-manufacturing D-glucaric acid and other bio-based chemicals.