Comparison of gut bacterial communities of Hyphantriacunea Drury (Lepidoptera, Arctiidae), based on 16S rRNA full-length sequencing

There are a large number of microorganisms in the gut of insects, which form a symbiotic relationship with the host during the long-term co-evolution process and have a significant impact on the host's nutrition, physiology, development, immunity, stress tolerance and other aspects. However, the composition of the gut microbes of Hyphantriacunea remains unclear. In order to investigate the difference and diversity of intestinal microbiota of H.cunea larvae feeding on different host plants, we used PacBio sequencing technology for the first time to sequence the 16S rRNA full-length gene of the intestinal microbiota of H.cunea. The species classification, β diversity and function of intestinal microflora of the 5th instar larvae of four species of H.cunea feeding on apricot, plum, redbud and Chinese ash were analysed. The results showed that a total of nine phyla and 65 genera were identified by PacBio sequencing, amongst which Firmicutes was the dominant phylum and Enterococcus was the dominant genus, with an average relative abundance of 59.29% and 52.16%, respectively. PERMANOVA analysis and cluster heat map showed that the intestinal microbiomes of H.cunea larvae, fed on different hosts, were significantly different. LEfSe analysis confirmed the effect of host diet on intestinal community structure and PICRUSt2 analysis showed that most of the predictive functions were closely related to material transport and synthetic, metabolic and cellular processes. The results of this study laid a foundation for revealing the interaction between the intestinal microorganisms of H.cunea and its hosts and provided ideas for exploring new green prevention and control strategies of H.cunea.

DNA sequencing reveals bacterial communities in midgut and other parts of the larvae of Spodoptera exigua Hubner (Lepidoptera: Noctuidae)

Gut microbiota has been suggested as an important component of host defense. However, microbiota in other parts of the body have rarely been characterized. In our present work, we give a detailed view of the body of Spodoptera exigua larvae, the midgut with intestinal contents (MG), midgut excluding intestinal contents (PM), intestinal contents (IC) and remaining parts excluding the MG (RM), with the objective of revealing the complexity of microorganisms and comparing the biodiversity of the S. exigua larvae-associated microbiota. Our results provide the first evidence that third and fifth larvae samples of S. exigua were dominated by members of the phyla Firmicutes and Proteobacteria. In addition, there were no obvious differences in relative abundances of microbiota among MG, PM and RM at the phylum level. MG3 and MG5 (nearly RM5) harbored the richest microbial community, with much higher abundance of Halomonas, Pseudomonas and Methylobacterium, respectively. Intestinal contents contained the lowest diversity and highest abundance of Enterococcus. Knowledge of the bacteria in a major herbivorous insect, such as S. exigua, can facilitate the acquisition of special biological resources for agricultural pest control.

In vivo Pyro-SIP assessing active gut microbiota of the cotton leafworm, Spodoptera littoralis

The gut microbiota is of crucial importance for the host with considerable metabolic activity. Although great efforts have been made toward characterizing microbial diversity, measuring components' metabolic activity surprisingly hasn't kept pace. Here we combined pyrosequencing of amplified 16S rRNA genes with in vivo stable isotope probing (Pyro-SIP) to unmask metabolically active bacteria in the gut of cotton leafworm (Spodoptera littoralis), a polyphagous insect herbivore that consumes large amounts of plant material in a short time, liberating abundant glucose in the alimentary canal as a most important carbon and energy source for both host and active gut bacteria. With (13)C glucose as the trophic link, Pyro-SIP revealed that a relatively simple but distinctive gut microbiota co-developed with the host, both metabolic activity and composition shifting throughout larval stages. Pantoea, Citrobacter and Clostridium were particularly active in early-instar, likely the core functional populations linked to nutritional upgrading. Enterococcus was the single predominant genus in the community, and it was essentially stable and metabolically active in the larval lifespan. Based on that Enterococci formed biofilm-like layers on the gut epithelium and that the isolated strains showed antimicrobial properties, Enterococcus may be able to establish a colonization resistance effect in the gut against potentially harmful microbes from outside. Not only does this establish the first in-depth inventory of the gut microbiota of a model organism from the mostly phytophagous Lepidoptera, but this pilot study shows that Pyro-SIP can rapidly gain insight into the gut microbiota's metabolic activity with high resolution and high precision.

Symbionts as major modulators of insect health: lactic acid bacteria and honeybees

Lactic acid bacteria (LAB) are well recognized beneficial host-associated members of the microbiota of humans and animals. Yet LAB-associations of invertebrates have been poorly characterized and their functions remain obscure. Here we show that honeybees possess an abundant, diverse and ancient LAB microbiota in their honey crop with beneficial effects for bee health, defending them against microbial threats. Our studies of LAB in all extant honeybee species plus related apid bees reveal one of the largest collections of novel species from the genera Lactobacillus and Bifidobacterium ever discovered within a single insect and suggest a long (>80 mya) history of association. Bee associated microbiotas highlight Lactobacillus kunkeei as the dominant LAB member. Those showing potent antimicrobial properties are acquired by callow honey bee workers from nestmates and maintained within the crop in biofilms, though beekeeping management practices can negatively impact this microbiota. Prophylactic practices that enhance LAB, or supplementary feeding of LAB, may serve in integrated approaches to sustainable pollinator service provision. We anticipate this microbiota will become central to studies on honeybee health, including colony collapse disorder, and act as an exemplar case of insect-microbe symbiosis.

Microbes, intestinal inflammation and probiotics

Inflammatory bowel disease (IBD) is known for causing disturbed homeostatic balance among the intestinal immune compartment, epithelium and microbiota. Owing to the emergence of IBD as a major cause of morbidity and mortality, great efforts have been put into understanding the sequence of intestinal inflammatory events. Intestinal macrophages and dendritic cells act in a synergistic fashion with intestinal epithelial cells and microbiota to initiate the triad that governs the intestinal immune responses (whether inflammatory or regulatory). In this review, we will discuss the interplay of intestinal epithelial cells, bacteria and the innate immune component. Moreover, whether or not genetic intervention of probiotic bacteria is a valid approach for attenuating/mitigating exaggerated inflammation and IBD will also be discussed.

Cleavage of PGRP-LC receptor in the Drosophila IMD pathway in response to live bacterial infection in S2 cells

Drosophila responds to Gram-negative bacterial infection by activating the immune deficiency (IMD) pathway, leading to production of antimicrobial peptides (AMPs). As a receptor for the IMD pathway, peptidoglycan-recognition protein (PGRP), PGRP-LC is known to recognize and bind monomeric peptidoglycan (DAP-type PGN) through its PGRP ectodomain and in turn activate the IMD pathway. The questions remain how PGRP-LC is activated in response to pathogen infection to initiate the IMD signal transduction in Drosophila. Here we present evidence to show that proteases such as elastase and Mmp2 can also activate the IMD pathway but not the TOLL pathway. The elastase-dependent IMD activation requires the receptor PGRP-LC. Importantly, we find that live Salmonella/E. coli infection modulates PGRP-LC expression/receptor integrity and activates the IMD pathway while dead Salmonella/E. coli or protease-deficient E. coli do neither. Our results suggest an interesting possibility that Gram-negative pathogen infection may be partially monitored through the structural integrity of the receptor PGRP-LC via an infection-induced enzyme-based cleavage-mediated activation mechanism.

Chronic activation of the epithelial immune system of the fruit fly's salivary glands has a negative effect on organismal growth and induces a peculiar set of target genes

Background

Epithelial and especially mucosal immunity represents the first line of defence against the plethora of potential pathogens trying to invade via the gastrointestinal tract. The salivary glands of the fruit fly are an indispensable part of the gastrointestinal tract, but their contribution to the mucosal immunity has almost completely been neglected. Our major goal was to elucidate if the fly's salivary glands are able to mount an immune response and what the major characteristics of this immune response are.

Results

Ectopic activation of the IMD-pathway within the salivary gland cells is able to induce an immune response, indicating that the salivary glands are indeed immune competent. This reaction is characterized by the concurrent expression of numerous antimicrobial peptide genes. In addition, ectopic activation of the salivary gland's immune response induces morphological changes such as dwarfism throughout all developmental stages and a significantly decreased length of the salivary glands themselves. DNA-microarray analyses of the reaction revealed a complex pattern of up- and downregulated genes. Gene ontology analyses of regulated genes revealed a significant increase in genes associated with ribosomal and proteasomal function. On the other hand, genes coding for peptide receptors and some potassium channels are downregulated. In addition, the comparison of the transcriptional events induced following IMD-activation in the trachea and the salivary glands shows also only a small overlap, indicating that the general IMD-activated core transcriptome is rather small and that the tissue specific component of this response is dominating. Among the regulated genes, those that code for signaling associated protease activity are significantly modulated.

Conclusions

The salivary glands are immune-competent and they contribute to the overall intestinal immune system. Although they produce antimicrobial peptides, their overall response is highly tissue-specific. Our analysis indicates that chronic activation of the salivary gland's immune system is costly, as it induces severe reduction in growth throughout development. The IMD-regulated increase in expression levels of the fly's presenilin representatives opens the opportunity to use the salivary glands for studying the physiological and pathophysiological role of these genes in a simple but functional environment.

Differential regulation of mRNA stability controls the transient expression of genes encoding Drosophila antimicrobial peptide with distinct immune response characteristics

The tight regulation of transiently expressed antimicrobial peptides (AMPs) with a distinct antimicrobial spectrum and different expression kinetics contributes greatly to the properly regulated immune response for resistance to pathogens and for the maintenance of mutualistic microbiota in Drosophila. The important role of differential regulation of AMP expression at the posttranscriptional level needs to be elucidated. It was observed that the highly expressed Cecropin A1 (CecA1) mRNA encoding a broad antimicrobial spectrum AMP against both bacteria and fungi decayed more quickly than did the moderately expressed Diptericin mRNA encoding AMP against Gram negative bacteria. The mRNA stability of AMPs is differentially regulated and is attributed to the specific interaction between cis-acting ARE in 3'-UTR of AMP mRNA and the RNA destabilizing protein transactor Tis11 as shown in co-immunoprecipitation of the Tis11 RNP complex with CecA1 mRNA but not other AMP mRNA. The p38MAPK was further demonstrated to play a crucial role in stabilizing ARE-bearing mRNAs by inhibiting Tis11-mediated degradation in LPS induced AMP expression. This evidence suggests an evolutionarily conserved and functionally important molecular basis for and effective approach to exact control of AMP gene expression. These mechanisms thereby orchestrate a well balanced and dynamic antimicrobial spectrum of innate immunity to resist infection and maintain resident microbiota properly.

Bacterial-modulated signaling pathways in gut homeostasis

Symbiotic mutualism with gut microbes occurs in all metazoans, and it is well established that commensal bacteria influence multiple aspects of host gut physiology such as innate immunity and development. However, our understanding of these coevolved interactions between prokaryotes and eukaryotes remains unclear. One mechanism by which commensal bacteria modulate host intracellular signaling pathways in order to avoid excess inflammation has now been determined. In this process, bacterial-induced reactive oxygen species in gut epithelial cells act as key messengers that inhibit the cullin-1-dependent protein degradation machinery, which in turn results in the stabilization of a master negative regulator of inflammation, inhibitor of nuclear factor-kappaB (IkappaB). Furthermore, this bacterial-mediated system also appears to be involved in the stabilization of a key developmental regulator, beta-catenin. These findings provide new insights into the molecular mechanisms by which commensal microbes shape host cellular physiology.