Production of bioethanol by bacterial co-culture from agro-waste-impacted soil through simultaneous saccharification and co-fermentation of steam-exploded bagasse

Abstract

Background: The production of bioethanol by co-culture of cellulolytic and xylanolytic bacteria isolated from agro-waste-impacted soil through simultaneous saccharification and co-fermentation (SSCF) of steam-exploded bagasse was investigated. Methods: The cellulolytic (VCE-19) and xylanolytic (VXE-41) isolates were screened using the Congo Red Plate Method. The DNS method was used in the determination of reducing sugar content. Chemical analysis of the sugarcane bagasse was determined using standard methods. The bagasse was subjected to steam explosion to reduce lignin content and enhance cellulose availability. Results: Mean proximate composition analysis of the bagasse showed total carbohydrate and lignin content (% dry weight) of 70.3 ± 1.9 and 19.2 ± 1.2 before pretreatment and 85.4 ± 2.33 and 4.2 ± 0.44 after pretreatment, respectively. Phylogenetic analysis based on partial sequence of the 16S rRNA gene classified VCE-19 and VXE-41 as Bacillus cereus GBPS9 and Bacillus thuringiensis serovar kurstaki HD1, respectively. The sequences obtained from these isolates have been submitted to GenBank and accession numbers (KT350986.1 for VXE-41 and KT318371.1 for VCE-19) assigned to them. The result of the optimization of cultural conditions of the bacterial co-culture revealed optimum cellulase production at the following conditions: temperature, 40 °C; pH, 7; substrate concentration, 4.0 % (w/v); inoculum concentration, 4 % (v/v) and when yeast extract was used as nitrogen source. The gas chromatography–mass spectrometry (GC–MS) analysis of the fermentation broth detected the following components: acetone (3.49 g/L), ethylacetate (8.75 g/L), ethanol (19.08 g/L), N-propanol (4.96 g/L), isobutanol (3.73 g/L) and acetic acid (6.53 g/L). Conclusions: This study has demonstrated the production of significant quantity of ethanol by a co-culture of B. cereus GBPS9 and B. thuringiensis serovar kurstaki HD1 through SSCF of steam-exploded bagasse. Efficient bioethanol production from bagasse can help solve the need for alternative source of energy and the crisis that results from bioethanol production from food and feed crops.