Demonstrating lignocellulolytic potential of actinobacteria for application in biomass processing
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Date
2021
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DIVISION OF MICROBIOLOGY ICAR- INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Recently, the deficiency of nonrenewable energy sources and environmental issues such as air pollution
and global warming has raised the demand of finding of an alternate carbon neutral renewable energy
resource. Lignocellulosic (LC) biomass is a great solution to it due to its low cost and natural abundance.
However its conversion and processing is challenging. Several methods including chemical, physical,
physico-chemical and biological are used to deconstruct LC biomass and increase enzyme accessibility
for cellulose and hemicellulose degradation. Biological processing is preferred due to its less energy
requirement, cost effectiveness and environment friendly nature. Several microbes like white rot fungi,
bacteria and actinomycetes have the ability to degrade lignocellulosic biomass in natural niches and
thesemicrobial consortia bring about global C cycle. One such habitat compost supports huge microbial
diversity and actinobacteria form dominant proportion of community.The presence of different pH and
temperature regimes in these habitats make actinobacteria potential sources of enzymes with desirable
properties in biomass processing and biorefineries. The current study was thus aimed at isolation and
characterization of actinobacterial strains for lignocellulolytic enzyme production and delignification of
rice straw for enhanced saccharification.
Of the thirteen actinobacterial strains isolated from compost samples after enrichment on rice straw at 40
ºC and pH 8, two strains were selected and found to be potentially significant lignocellulose degraders
through qualitative and quantitative enzymes assays of lignocelluloytic enzymes. Both were identified to
be Streptomyces thermoviolaceous S1 and Streptomyces thermophilus S2 by PCR based molecular
characterization. Under submerged fermentation, production of lignocellulolytic enzymes (CMCase,
FPase, β-glucosidase, Xylanase, Laccase, Lignin peroxidase) was favoured in presence of rice straw as a
carbon substrate than cellulose. Except β-glucosidase all enzyme activities were found to be more at 21st
day of incubation compared to 10th day of incubation. Under solid state fermentation, higher lignin
degradation by S. thermophilus S2 was observed, asevident from higher absorbance in alkali extracts of
fermented rice straw at 205 nm. Higher enzymatic activities were obtained in buffer extracts of S.
thermophilus S2 inoculated rice straw during solid state fermentation compared to S. thermoviolaceus S1.
Removal of lignin resulted in enrichment of 53.03% and 49.01% holocellulose with S. thermophilus S2
and S. thermoviolaceus S1 respectively correlating with the levels of degraded lignin in its alkali extracts.
Structural and compositional analysis using electron microscope, XRD and FTIR also provided the
evidence for cellulose disintegration and lignin removal in pretreated rice straw compared to uninoculated
rice straw. Buffer extracts of solid state fermented rice straw were found to be good source of
lignocellulolytic enzymes for biomass hydrolysis. These findings highlight S. thermophilus S2 and S.
thermoviolaceus S1 are promising source of enzymes and biocatalysts for biomass processing.
Description
T-10553