Enhanced saccharification of lignocellulosic agricultural biomass and increased bioethanol titre using acclimated Clostridium thermocellum DSM1313

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.

Keywords: Acclimation; Cellobiose; Clostridium thermocellum; Ethanol; Lignocellulose; Reducing sugars.

Fig. 1

FESEM micrographs. a Untreated SB, a1 treated SB, detached fibrils are depicted in the circle. b Untreated BP, b1 treated BP, lignin particles attached to the fibres depicted in the circle. c Untreated RH, c1 treated RH. Magnification scale bar is illustrated in each image

Fig. 2

a FTIR spectrum of untreated and treated SB. b FTIR spectrum of untreated and treated BP. c FTIR spectrum of untreated and treated RH

Fig. 2

a FTIR spectrum of untreated and treated SB. b FTIR spectrum of untreated and treated BP. c FTIR spectrum of untreated and treated RH

Fig. 3

a Different growth pattern of Clostridium thermocellum in the standard cellulose and cellobiose media. In cellobiose media organism depicted an early catch up and increased OD₆₀₀ values compared to cellulose media. However, the growth pattern was similar in both media. b Graphical representation of calculated f.RS from Clostridium thermocellum inoculated in cellobiose and cellulose medium. f.RS values from cellobiose media was <1, indicating its consumption by the organism and in cellulose media the f.RS value was >1 and increased each day indicating the release of reducing sugar due to hydrolysis exceeding the consumption rate of the organism