Abstract
Consolidated bioprocess assures an efficient lignocellulosic conversion to fermentable sugars and subsequently to bioethanol. Such a single-step hydrolysis and anaerobic fermentation was achieved with acclimated Clostridium thermocellum DSM 1313 on different mildly pre-treated agricultural lignocellulosic residues without any additional enzymes/and strains. Acclimation was achieved by serially sub-culturing in increasing concentration of individual substrates, such as rice husk, sugarcane bagasse, and banana pseudostem in the standard media, with cellobiose as an adjunct. The acclimated cellulolytic thermophile exhibited an early log phase entry with enhanced growth compared to the direct inoculation experiments with unacclimated culture. Around 672 mg/g of reducing sugar was produced from sugarcane bagasse media and 636 mg/g from rice husk media and 513 mg/g from banana pseudostem media with the acclimated organism. Bioethanol production also doubled in experiments with serially acclimated cultures, with a maximum of 1.21 and 1.0 g/L ethanol titre from sugarcane bagasse and rice husk, respectively. The serial acclimation experiments have increased the saccharification potentials of the organism towards the respective lignocellulosic substrates and also enhanced the bioethanol production.
Highlights
The first-generation biofuels have promoted edible crops as feedstocks for bioethanol production
This study explains the strategy of developing hydrolysate rich in mono-sugars from lignocellulosic substrates (LCSs) for consequent ethanol production using Clostridium thermocellum
The pure strain of Clostridium thermocellum was successfully acclimated by serially incubating in increasing concentrations of respective LCSs with cellobiose as growth inducer
Summary
The first-generation biofuels have promoted edible crops as feedstocks for bioethanol production. Secondgeneration biofuels are considered as advanced biofuels, since the feedstock generally used is not food crops, such as in first-generation biofuels Various methods, such as physico-chemical/and enzymatic hydrolytic techniques, have been used for converting lignocellulosic composite to reducing sugars for bioethanol production. Clostridium thermocellum is an anaerobic, spore-forming cellulolytic thermophile producing multi-enzyme complex consisting of various hydrolytic enzymes as well as extracellular individual free enzymes. Having both these enzyme systems is a rare characteristic in the microbial world due to which C. thermocellum is an efficient biomass degrader along with ethanolgenic capabilities (Wilson 2011; Paye et al 2016). Irrespective of the technological advancements, the technical and economic constrains of converting the cellulosic material into fermentable sugars for the production of biofuels remain unsolved
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