Detoxifying symbiosis in Nezara viridula

The Southern green shield bug, Nezara viridula, is an invasive piercing and sucking pest insect that feeds on leguminous crops and poses a threat to global food production. Insects are known to live in a close relationship with microorganisms, which provide hosts with unique capabilities, such as resistance to toxic secondary plant metabolites, e.g. 3-nitropropionic acid. In this study, we sequenced isolated members of N. viridula microbial gut community and analysed phylogenetic markers of toxin-degrading genes. We combined it with culturing eight bacterial isolates on 3-nitroproponic acid-rich agar plates and in liquid media to assess their resistance and ability to metabolize toxins. We showed that core- and transient-associated gut microorganisms had different tolerance to high concentrations of the toxin and that six strains detoxified 3-nitropropionic acid. Using transcriptomics and untargeted metabolomics approaches, we revealed that the toxin might influence the metabolism and transport of amino acids, particularly leucine biosynthesis. Also, we investigated pairwise microbial interactions between members of the gut community are found that core microbiota shapes the composition of the N. viridula microbiome by favouring the growth of symbiotic microorganisms and suppression of transient bacteria. With this research, we provided novel insights into the microbial role in shaping the insect gut community and demonstrated that N. viridula harbours many toxin-degrading bacteria that could support its resistance to plant defences.