Annotation of gut bacterial taxonomic and functional diversity in Spodoptera litura and Spilosoma obliqua

Abstract

The insect gut has been the house of many taxonomically and physiologically diverse groups of microbial colonizers as symbionts and commensals, which are evolving to support the physiological requirement of insects. Lepidoptera is one of the important family of class hexapoda, comprising agriculture insect pest Spodoptera litura and Spilosoma obliqua. Information on gut microbiota and their functional role in these insects was meager to elucidate the wide-ranging survivalist mechanisms. In this context, we analyzed the composition, diversity and functional role of gut bacteria in S. litura and S. obliqua collected from soybean and sunflower crops, respectively, using Next Generation Sequencing of 16S rRNA. A total of 3427 and 206 Operation Taxonomic Units (OTUs) were identified in S. litura and S. obliqua gut metagenome, respectively. Highest number of sequences were annotated to unclassified bacteria (34%), followed by Proteobacteria (27%), and Chlorobi (14%) in S. litura, while S. obliqua has significant representation of Firmicutes (48%), followed by Bacteroidetes (20%), and unclassified bacteria (11%). Functionality of both metagenomes revealed, high abundance of ammonia oxidizers (20.1 58.0%) followed by relative abundance of detoxifying processes - dehalogenation (17.4-41.2%) and aromatic hydrocarbons degradation (1.1-3.1%). This study highlights the significance of the inherent microbiome of two defoliators in shaping the metagenome for nutrition and detoxifying the chemical molecules, and opens an avenue for exploring role of insect gut bacteria in host selection, metabolic endurance of insecticides and synergistic or agonistic mechanisms inside gut of insects feeding on insect-resistant biotech crops.

Gut microbiota ofSpodoptera frugiperda(J.E. Smith) larvae as revealed by metatranscriptomic analysis

“…These results are in accordance with a recent study that used high‐throughput sequencing of 16S rDNA to analyse the gut microbiota of late‐instar field‐captured H. armigera larvae, where Actinobacteria was the dominant phylum followed by Proteobacteria and Firmicutes (Ranjith et al, ). Moreover, in another study that also used next‐generation sequencing of 16S rDNA, a very high proportion of the S. litura larval gut microbiota corresponded to uncultured Bacteria (Bapatla et al, ). Nevertheless, two other studies that analysed the gut microbiota in S. littoralis found that, in late‐instar larvae, both taxonomically and metabolically (although in different proportions), Firmicutes was by far the most abundant phylum, followed by Proteobacteria, and that Enterococcus (Firmicutes) was the most active genus, and to a lesser degree, Clostridium (Firmicutes) and Pantoea (Proteobacteria; Chen et al, ; Shao et al, ).…”

“…One of these studies showed that bacteria isolated from the P. xylostella gut had the ability to fix nitrogen in vitro (Indiragandhi et al, ). The other study analysed the gut metagenome of S. litura and Spilosoma obliqua Walker (Lepidoptera: Erebidae) through high‐throughput sequencing of 16S rDNA and indirectly inferred a high abundance of bacterial ammonia oxidizers by taxonomic to phenotypic mapping of the datasets (Bapatla et al, ; Table S6). Our study strongly suggests that Bacteria and Archaea were expressing transcripts associated with nitrogen utilization in the larval guts of field‐captured S. frugiperda , likely due to their great voracity and ensuing need to metabolize the ingested nitrogen.…”

“…To conclude, various studies have analysed the gut microbiota of insects, and a high proportion of these have used next‐generation sequencing approaches. These studies have mostly focused on the taxonomic composition of the microbiome through analysis of the rRNA gene, and some have also inferred the functional profile (Bapatla et al, ; Ranjith et al, ; Tang et al, ), but very few have determined the metabolically active components (Chen et al, ; Shao et al, ). Moreover, in most of these studies the focus has been on the bacterial community, with little or no integration with the rest of the non‐bacterial microbiota.…”

“…Furthermore, studies describing the microbiome in lepidopterans are few and have mostly focused on Spodoptera littoralis (Boisduval; Chen et al, ; Shao, Arias‐Cordero, Guo, Bartram, & Boland, ; Shao et al, ; Tang et al, ), Plutella xylostella (L.) (Indiragandhi et al, ; Li, Jin, Shi, & Li, ; Xia et al, ), Helicoverpa armigera (Hübner; Priya, Ojha, Kajla, Raj, & Rajagopal, ; Ranjith, ManiChellappan, Harish, Girija, & Nazeem, ), Plodia interpunctella (Hübner; Mereghetti, Chouaia, Limonta, Locatelli, & Montagna, ; Montagna et al, ), Anticarsia gemmatalis (Hübner; Visôtto et al, ), Spodoptera litura (Fabr. ; Bapatla, Singh, Yeddula, & Patil, ) and Lymantria dispar (L.) (Broderick, Raffa, Goodman, & Handelsman, ). In the case of S. frugiperda , only one study used culture‐dependent methods to isolate gut bacteria from the oral secretions of field‐collected larvae, and the authors concluded that the bacterial isolates regulated herbivore‐induced defences (Acevedo et al, ).…”

Characterization of Spodoptera litura Gut Bacteria and Their Role in Feeding and Growth of the Host

“…Previous studies have begun to explore gut microbial diversity and function of S. litura . Bapatla et al (2018) used the V3 region of 16S rRNA to amplify the gut bacteria in S. litura and then sequenced them on the Illumina MiSeq platform, revealing that the gut bacteria of S. litura were composed of 27% Proteobacteria and 14% Chlorobi. Proteobacteria was the most abundant phylum in the S. litura gut, however, 34% of unclassified bacteria in the V3 region were relatively short and difficult to annotate ( Bapatla et al, 2018 ).…”