Gut microorganisms of Locusta migratoria in various life stages and its possible influence on cellulose digestibility

Locusta migratoria is an important phytophagous pest, and its gut microbial communities play an important role in cellulose degradation. In this study, the gut microbial and cellulose digestibility dynamics of Locusta migratoria were jointly analyzed using high-throughput sequencing and anthrone colorimetry. The results showed that the gut microbial diversity and cellulose digestibility across life stages were dynamically changing. The species richness of gut bacteria was significantly higher in eggs than in larvae and imago, the species richness and cellulose digestibility of gut bacteria were significantly higher in early larvae (first and second instars) than in late larvae (third to fifth instars), and the diversity of gut bacteria and cellulose digestibility were significantly higher in imago than in late larvae. There is a correlation between the dynamics of gut bacterial communities and cellulose digestibility. Enterobacter, Lactococcus, and Pseudomonas are the most abundant genera throughout all life stages. Six strains of highly efficient cellulolytic bacteria were screened, which were dominant gut bacteria. Carboxymethyl cellulase activity (CMCA) and filter paper activity (FPA) experiments revealed that Pseudomonas had the highest cellulase enzyme activity. This study provides a new way for the screening of cellulolytic bacteria and lays the foundation for developing insects with significant biomass into cellulose-degrading bioreactors.

IMPORTANCE

Cellulose is the most abundant and cheapest renewable resource in nature, but its degradation is difficult, so finding efficient cellulose degradation methods is an urgent challenge. Locusta migratoria is a large group of agricultural pests, and the large number of microorganisms that inhabit their intestinal tracts play an important role in cellulose degradation. We analyzed the dynamics of Locusta migratoria gut microbial communities and cellulose digestibility using a combination of high-throughput sequencing technology and anthrone colorimetry. The results revealed that the gut microbial diversity and cellulose digestibility were dynamically changed at different life stages. In addition, we explored the intestinal bacterial community of Locusta migratoria across life stages and its correlation with cellulose digestibility. The dominant bacterial genera at different life stages of Locusta migratoria were uncovered and their carboxymethyl cellulase activity (CMCA) and filter paper activity (FPA) were determined. This study provides a new avenue for screening cellulolytic bacteria and lays the foundation for developing insects with significant biomass into cellulose-degrading bioreactors.

Changes in the bacterial communities of Harmonia axyridis (Coleoptera: Coccinellidae) in response to long-term cold storage and progressive loss of egg viability in cold-stored beetles

Bacteria have a profound influence on life history and reproduction of numerous insects, while the associations between hosts and bacteria are substantially influenced by environmental pressures. Cold storage is crucial for extending the shelf life of insects used as tools for biological control, but mostly causes detrimental effects. In this study, we observed a great decrease in egg hatch rate of cold-stored Harmonia axyridis during the later oviposition periods. Furthermore, most eggs produced by their F1 offspring exhibited complete loss of hatchability. We hypothesized that long-term exposure to cold may greatly alter the bacterial community within the reproductive tracts of H. axyridis, which may be an important factor contributing to the loss of egg viability. Through sequencing of the 16S rRNA gene, we discovered considerable changes in the bacterial structure within the reproductive tracts of female cold-stored beetles (LCS_F) compared to non-stored beetles (Control_F), with a notable increase in unclassified_f_Enterobacteriaceae in LCS_F. Furthermore, in accordance with the change of egg hatchability, we observed a slight variation in the microbial community of eggs produced by cold-stored beetles in early (Egg_E) and later (Egg_L) oviposition periods as well as in eggs produced by their F1 offspring (Egg_F1). Functional predictions of the microbial communities revealed a significant decrease in the relative abundance of substance dependence pathway in LCS_F. Moreover, this pathway exhibited relatively lower abundance levels in both Egg_L and Egg_F1 compared to Egg_E. These findings validate that long-term cold storage can greatly modify the bacterial composition within H. axyridis, thereby expanding our understanding of the intricate bacteria-insect host interactions.

Environment-Dependent Variation in Gut Microbiota of an Oviparous Lizard (Calotes versicolor)

Simple Summary

The different gut sections potentially provide different habitats for gut microbiota. We found that Bacteroidetes, Firmicutes, and Proteobacteria were the three primary phyla in gut microbiota of C. versicolor. The relative abundance of dominant phyla Bacteroidetes and Firmicutes exhibited an increasing trend from the small intestine to the large intestine, and there was a higher abundance of genus Bacteroides (Class: Bacteroidia), Coprobacillus and Eubacterium (Class: Erysipelotrichia), Parabacteroides (Family: Porphyromonadaceae) and Ruminococcus (Family: Lachnospiraceae), and Family Odoribacteraceae and Rikenellaceae in the hindgut, and some metabolic pathways were higher in the hindgut. Our results reveal the variations of gut microbiota composition and metabolic pathways in different parts of the lizards’ intestine.

Abstract

Vertebrates maintain complex symbiotic relationships with microbiota living within their gastrointestinal tracts which reflects the ecological and evolutionary relationship between hosts and their gut microbiota. However, this understanding is limited in lizards and the spatial heterogeneity and co-occurrence patterns of gut microbiota inside the gastrointestinal tracts of a host and variations of microbial community among samples remain poorly understood. To address this issue and provide a guide for gut microbiota sampling from lizards, we investigated the bacteria in three gut locations of the oriental garden lizard (Calotes versicolor) and the data were analyzed for bacterial composition by 16S ribosomal RNA (16S rRNA) gene amplicon sequencing. We found the relative abundance of the dominant phyla exhibited an increasing trend from the small intestine to the large intestine, and phyla Firmicutes, Bacteroidetes and Proteobacteria were the three primary phyla in the gut microbiota of C. versicolor. There were a higher abundance of genus Bacteroides (Class: Bacteroidia), Coprobacillus and Eubacterium (Class: Erysipelotrichia), Parabacteroides (Family: Porphyromonadaceae) and Ruminococcus (Family: Lachnospiraceae), and Family Odoribacteraceae and Rikenellaceae in the sample from the hindgut. The secondary bile acid biosynthesis, glycosaminoglycan degradation, sphingolipid metabolism and lysosome were significantly higher in the hindgut than that in the small intestine. Taken together our results indicate variations of gut microbiota composition and metabolic pathway in different parts of the oriental garden lizard.

The maternal foam plug constitutes a reservoir for the desert locust's bacterial symbionts

A hallmark of the desert locust's ancient and deserved reputation as a devastating agricultural pest is that of the long-distance, multi-generational migration of locust swarms to new habitats. The bacterial symbionts that reside within the locust gut comprise a key aspect of its biology, augmenting its immunity and having also been reported to be involved in the swarming phenomenon through the emission of attractant volatiles. However, it is still unclear whether and how these beneficial symbionts are transmitted vertically from parent to offspring. Using comparative 16S rRNA amplicon sequencing and direct experiments with engineered bacteria, we provide evidence for vertical transmission of locust gut bacteria. The females may perform this activity by way of inoculation of the egg-pod's foam plug, through which the larvae pass upon hatching. Furthermore, analysis of the composition of the foam revealed chitin to be its major component, along with immunity-related proteins such as lysozyme, which could be responsible for the inhibition of some bacteria in the foam while allowing other, more beneficial, strains to proliferate. Our findings reveal a potential vector for the transgenerational transmission of symbionts in locusts, which contributes to the locust swarm's ability to invade and survive in new territories.

Locust Bacterial Symbionts: An Update

As one of the world's most infamous agricultural pests, locusts have been subjected to many in-depth studies. Their ability at one end of their behavioral spectrum to live as solitary individuals under specific conditions, and at the other end of the spectrum to form swarms of biblical scale, has placed them at the focus of vast research efforts. One important aspect of locust ecology is that of their interactions with the bacteria that reside in and on them. Although this aspect of locust ecology has been little studied relative to the mainstream locust research, these bacteria have been shown both to affect locust immunity and to participate in maintaining swarm integrity through the secretion of attractant volatiles. The interaction between locusts and their bacteria seems, however, to be bi-directional, with the bacteria themselves, as recently shown, being influenced by their host's swarming tendencies. This seems to be a consequence of the bacterial composition in the locust's gut, reproductive organs, and integument undergoing change with the change in their host's behavior. In this review we describe the current state of knowledge of the locust-bacteria interactions (data exists mainly for the desert and the migratory locusts), as well as highlighting some newly-gained understanding; and offer perspectives for future research.