Evaluation of cellulose degrading bacteria isolated from the gut-system of cotton bollworm, Helicoverpa armigera and their potential values in biomass conversion

Abstract

Background Cotton bollworm, Helicoverpa armigera is a widely distributed, devastating pest of over 200 crop plants that mainly consist of some cellulosic materials. Despite its economic importance as a pest, little is known about the diversity and community structure of gut symbiotic bacteria potentially functioned in cellulose digestion in different gut-sections of H. armigera. In view of this lacuna, we attempted to evaluate and characterize cellulose-degrading bacteria (CDB) from foregut, midgut, and hindgut -regions of H. armigera by using a culture-dependent approach. Methodology The symbiotic bacteria were isolated from different gut-systems of H. armigera by enrichment techniques using Carboxymethyl cellulose sodium salt (CMC) as carbon source. The isolated bacteria were purified and subsequently screened for cellulose-degradation by plate-based method to display the zones of CMC clearance around the colonies. The identification and phylogeny of the gut-bacteria were reconstructed by using 16S rRNA gene sequencing. Different enzymes such as endoglucanase, exoglucanase, β-glucosidase, and xylanase were assayed to determine the cellulolytic repertoire of the isolated bacteria. Results The enrichment of CDB and subsequent plate based screening methods resulted in isolation of 71 bacteria among which 54% of the bacteria were obtained from foregut. Among the isolated bacteria, 25 isolates showed discernible cellulose-degradation potential on CMC-agar plates. The phylogenetic analysis based on 16S rRNA gene amplification and sequencing affiliated these cellulolytic bacteria to two major phyla viz., Firmicutes and Proteobacteria. The members of the genus Klebsiella accounted for 39.43% of the total isolated bacteria while 31% of the Bacillus strains were enriched from hindgut region. The principal component analysis (PCA) further suggested that the members of Bacillus and Klebsiella together dominated the foregut and hindgut regions as they accounted for 68% of the total CDB. The four potential isolates selected on the basis of plate-based activities were further evaluated for their lignocellulases production by using various agricultural wastes as substrates. The PCA of the enzyme activities demonstrated that potential isolates majorly secreted endoglucanase and xylanase enzymes. Among the agro-wastes, multivariate analysis validated wheat husk (WH) and sugarcane bagasse (SCB) as most favorable substrates for xylanase and endoglucanase productions respectively. The overall findings suggest that H. armigera harbors diverse bacterial communities in different gut-sections that could assist the host in digestion processes, which may potentially serve as a valuable reservoir of some unique symbionts applied for biomass conversion in biofuel industry.

Exploring the region‐wise diversity and functions of symbiotic bacteria in the gut system of wood‐feeding termite, Coptotermes formosanus, toward the degradation of cellulose, hemicellulose, and organic dyes

“…A single colony of each isolate was suspended in sterilized PBS from which 20 μ L of each suspension was inoculated into DSM agar wells containing 0.15% aniline blue dye as a lignin analog. The culture plates were incubated at 30 °C for a minimum period of 96 h. Thereafter, the cellulose and xylan‐containing plates were flooded with Gram's iodine solution for 5 min as described previously (Dar et al ., 2021b) to observe the yellowish zone of substrate degradation. In the case of dye decolorization, bacteria showing zones of substrate clearance around the colonies were considered capable of degrading aniline blue dye.…”

Microbial gut diversity in four grasshopper species and its correlation with cellulose digestibility

“…Gut microorganisms of insects and ruminants play an important role in the degradation of lignocellulose, and synergistic microbial symbioses can make a significant contribution to the recovery of renewable carbon from lignocellulose, which is difficult to degrade ( Rajeswari et al, 2021 ). Enterobacter , Bacillus and Klebsiella isolated from Spodoptera frugiperda , Proisotoma ananevae , and Helicoverpa armigera have cellulose-degrading abilities ( Wang et al, 2018 ; Li et al, 2020 ; Dar et al, 2021 ). Bacillus flexus has been shown to be a potential cellulose-degrading bacterium with additional lignocellulose-degrading ability ( Sanchez-Gonzalez et al, 2011 ; Sreeremya and Rajiv, 2017 ; Kumar et al, 2020 ).…”

“…There are more than one million species of insects, making them the most diverse group of animals ( Mei et al, 2018 ). Correspondingly, insects have evolved complex and highly specialized intestinal systems to digest a variety of food sources; thus, the insect gut system has been designated as the world’s smallest natural bioreactor ( Breznak and Brune, 1994 ; Dar et al, 2021 ). The complex structure and large surface area to volume ratio of the insect gut provides a habitat for many intestinal microorganisms and guarantees a rich biodiversity ( Brune and Dietrich, 2015 ).…”

Valorization Potential of a Novel Bacterial Strain, Bacillus altitudinis RSP75, towards Lignocellulose Bioconversion: An Assessment of Symbiotic Bacteria from the Stored Grain Pest, Tribolium castaneum

“…Although the occurrence of endogenous cellulases in T. castaneum was reported recently [19][20][21][22], not much is known about the cellulolytic microbes inhabiting its gut system. Additionally, unlike other insects such as termites [23,24], Lepidoptera [12,25], orthopterans [26], and dung beetles [27,28], bacterial cellulases and their activities from the gut of T. castaneum have not been studied yet. Hence, the prospection of cellulolytic bacteria in T. castaneum would not only contribute to the basic understanding of host-microbe interactions but would also highlight its prospective applications for the discovery and bioengineering of potential bacteria and their use in biorefinery and pulp industry alongside biofuel production.…”