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.

中文翻译：

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从棉铃虫，棉铃虫肠道系统分离的纤维素降解细菌及其在生物量转化中的潜在价值的评价

背景技术棉铃虫（Helicoverpa armigera）是一种分布广泛的毁灭性害虫，有200多种农作物，主要由某些纤维素材料组成。尽管它在经济上作为害虫很重要，但对棉铃虫不同肠段纤维素消化中潜在起作用的肠道共生细菌的多样性和群落结构知之甚少。鉴于这种缺陷，我们试图通过使用依赖于培养物的方法来评估和鉴定棉铃虫前肠，中肠和后肠区域的纤维素降解细菌（CDB）。方法学采用羧甲基纤维素钠盐（CMC）作为碳源，通过富集技术从棉铃虫不同肠道系统分离共生细菌。纯化分离的细菌，随后通过基于平板的方法筛选纤维素降解情况，以显示菌落周围的CMC清除区域。通过使用16S rRNA基因测序重建肠道细菌的鉴定和系统发育。分析了不同的酶，例如内切葡聚糖酶，外切葡聚糖酶，β-葡萄糖苷酶和木聚糖酶，以确定分离细菌的纤维素分解库。结果CDB的富集和随后的基于板的筛选方法导致分离出71种细菌，其中54％的细菌来自前肠。在分离出的细菌中，有25个分离株在CMC-琼脂平板上显示出可分辨的纤维素降解潜能。基于16S rRNA基因扩增和测序的系统发育分析将这些纤维素分解细菌与两个主要的门菌相关，即Firmicutes和Proteobacteria。克雷伯菌属的成员占分离细菌总数的39.43％，而芽孢杆菌菌株的31％从后肠区富集。主成分分析（PCA）进一步表明，芽孢杆菌和克雷伯菌的成员共同主导了前肠和后肠区域，因为它们占总CDB的68％。通过使用各种农业废料作为底物，进一步评估了基于板活动选择的四种潜在分离物的木质纤维素酶生产。酶活性的PCA表明，潜在的分离物主要分泌内切葡聚糖酶和木聚糖酶。在农业废料中，多变量分析验证了小麦皮（WH）和甘蔗渣（SCB）分别是木聚糖酶和内切葡聚糖酶生产的最有利底物。总体研究结果表明，棉铃虫在不同的肠段中具有多样的细菌群落，可以帮助宿主消化，这可能是一些独特的共生生物的宝贵资源，这些共生生物用于生物燃料工业中的转化。