Nanopore-Sequencing Characterization of the Gut Microbiota of Melolontha melolontha Larvae: Contribution to Protection against Entomopathogenic Nematodes?

Ewa Sajnaga,Adrian Wiater,Magdalena Lis,Karolina Ferenc,Marcin Skowronek,Waldemar Kazimierczak,Agnieszka Kalwasińska

doi:10.3390/pathogens10040396

Abstract

This study focused on the potential relationships between midgut microbiota of the common cockchafer Melolontha melolontha larvae and their resistance to entomopathogenic nematodes (EPN) infection. We investigated the bacterial community associated with control and unsusceptible EPN-exposed insects through nanopore sequencing of the 16S rRNA gene. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant bacterial phyla within the complex and variable midgut microbiota of the wild M. melolontha larvae. The core microbiota was found to include 82 genera, which accounted for 3.4% of the total number of identified genera. The EPN-resistant larvae differed significantly from the control ones in the abundance of many genera belonging to the Actinomycetales, Rhizobiales, and Clostridiales orders. Additionally, the analysis of the microbiome networks revealed different sets of keystone midgut bacterial genera between these two groups of insects, indicating differences in the mutual interactions between bacteria. Finally, we detected Xenorhabdus and Photorhabdus as gut residents and various bacterial species exhibiting antagonistic activity against these entomopathogens. This study paves the way to further research aimed at unravelling the role of the host gut microbiota on the output of EPN infection, which may contribute to enhancement of the efficiency of nematodes used in eco-friendly pest management.

Highlights

The insect gut is an organ with a highly diverse structure and a rich symbiotic community, which contains mostly bacteria and archaea, fungi, viruses, and protozoa [1,2].The composition of insect gut microbiota has been extensively explored with the use of high-throughput DNA sequencing techniques over the last decade, circumventing the limitations of culture-based methods [3]
We characterized the midgut bacterial communities of 27 M. melolontha L2 and L3 larva samples collected from soils of eastern Poland, of which 13 larvae were selected in the laboratory as entomopathogenic nematodes (EPN)- resistant (Table 1, Figure S1)
In the EPN-exposed unsusceptible larvae, we found a significant increase in the abundance of several bacterial genera belonging to the orders Actinomycetales and Rhizobiales, while the abundance of some other Clostridiales decreased

Summary

Introduction

The composition of insect gut microbiota has been extensively explored with the use of high-throughput DNA sequencing techniques over the last decade, circumventing the limitations of culture-based methods [3]. It seems that the diet, habitat, host taxonomy, and developmental stage determine gut assemblies most significantly [4,5]. Intestine residents can confer a wide array of advantages for the host through involvement in e.g., nutrition, development, communication, or detoxification They can protect their hosts against pathogens and parasites, which can be achieved indirectly by enhancing the insect innate immune system or intestinal epithelium cell regeneration and directly by competition for nutrients and space or production of antagonist compounds [1,6,7]. Based on their diverse abilities, the potential application of insect gut bacteria in medicine and industry is being recognized [12,13,14]

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Discussion

Conclusion