Abstract
Bioconversion of lignocellulose into renewable energy and commodity products faces a major obstacle of inefficient saccharification due to its recalcitrant structure. In nature, lignocellulose is efficiently degraded by some insects, including termites and beetles, potentially due to the contribution from symbiotic gut bacteria. To this end, the presented investigation reports the isolation and characterization of cellulolytic bacteria from the gut system of red flour beetle, Tribolium castaneum. Out of the 15 isolated bacteria, strain RSP75 showed the highest cellulolytic activities by forming a clearance zone of 28 mm in diameter with a hydrolytic capacity of ~4.7. The MALDI-TOF biotyping and 16S rRNA gene sequencing revealed that the strain RSP75 belongs to Bacillus altitudinis. Among the tested enzymes, B. altitudinis RSP75 showed maximum activity of 63.2 IU/mL extract for xylanase followed by β-glucosidase (47.1 ± 3 IU/mL extract) which were manifold higher than previously reported activities. The highest substrate degradation was achieved with wheat husk and corn cob powder which accounted for 69.2% and 54.5%, respectively. The scanning electron microscopy showed adhesion of the bacterial cells with the substrate which was further substantiated by FTIR analysis that depicted the absence of the characteristic cellulose bands at wave numbers 1247, 1375, and 1735 cm−1 due to hydrolysis by the bacterium. Furthermore, B. altitudinis RSP75 showed co-culturing competence with Saccharomyces cerevisiae for bioethanol production from lignocellulose as revealed by GC-MS analysis. The overall observations signify the gut of T. castaneum as a unique and impressive reservoir to prospect for lignocellulose-degrading bacteria that can have many biotechnological applications, including biofuels and biorefinery.
Highlights
The rapid depletion of fossil fuels and increased emission of greenhouse gases are the major issues of modern civilization that demand immediate addressal
The gut bacterium B. altitudinis RSP75 isolated in the present study showed good cellulolytic activities at pH 5.0 (p < 0.001), indicating it as the most suitable pH for cellulose degradation (Figure 4A)
The present study demonstrated the gut of T. castaneum to be a unique and potential resource for the bioprospection of efficient cellulose-degrading bacteria
Summary
The rapid depletion of fossil fuels and increased emission of greenhouse gases are the major issues of modern civilization that demand immediate addressal. These issues have attracted much attention from scientists and academicians as well as policy makers all over the world. LCbased agro-waste is mostly composed of three polymers, cellulose, hemicellulose, and lignin, among which cellulose and hemicellulose represent a major reservoir of fermentable sugars. Using advanced technologies, this promising, low-cost, and renewable energy resource can be transformed into a variety of useful products such as amino acids, sugars, biofuels, etc
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