8-HQA adjusts the number and diversity of bacteria in the gut microbiome of Spodoptera littoralis

Abstract

Quinolinic carboxylic acids are known for their metal ion chelating properties in insects, plants and bacteria. The larval stages of the lepidopteran pest, Spodoptera littoralis, produce 8-hydroxyquinoline-2-carboxylic acid (8-HQA) in high concentrations from tryptophan in the diet. At the same time, the larval midgut is known to harbor a bacterial population. The motivation behind the work was to investigate whether 8-HQA is controlling the bacterial community in the gut by regulating the concentration of metal ions. Knocking out the gene for kynurenine 3-monooxygenase (KMO) in the insect using CRISPR/Cas9 eliminated production of 8-HQA and significantly increased bacterial numbers and diversity in the larval midgut. Adding 8-HQA to the diet of knockout larvae caused a dose-dependent reduction of bacterial numbers with minimal effects on diversity. Enterococcus mundtii dominates the community in all treatments, probably due to its highly efficient iron uptake system and production of the colicin, mundticin. Thus host factors and bacterial properties interact to determine patterns of diversity and abundance in the insect midgut.

Comparative genomics of pesticide-degradingEnterococcussymbionts ofSpodoptera frugiperda(Lepidoptera: Noctuidae) leads to the identification of two new species and the reappraisal of insect-associatedEnterococcusspecies

“…Lepidopterans are also known to host a range of microbes, with bacteria mainly inhabiting the gut lumen [12,13]. Early studies on the microbial association with the lepidopteran gut disbelieved the existence of intimate microbial partnerships [14], but several other studies with lepidopteran larvae have demonstrated that gut bacteria can aid in food digestion [15], provide nutrients [16] and antimicrobials to regulate pathogens in the host gut microbiota [17] and participate in the metabolization of host plant-derived defense molecules [18,19] and pesticides [20][21][22].…”

Genomics of insecticide-metabolizing bacteria associated with >i<Spodoptera frugiperda>/i< (Lepidoptera: Noctuidae) and their potential role in host detoxification

“…However, subsequent research on lepidopteran larvae has demonstrated that gut bacteria play crucial roles in food digestion facilitation [15], nutrient absorption enhancement [12], and direct contribution to host nutrition through production of essential nutrients (eg, L-tryptophan) [16]. Yet, gut bacteria of lepidopteran larvae can inhibit potentially harmful microorganisms by producing antimicrobial compounds [17] and reduce the toxicity of xenobiotics by the metabolization of host plantderived defense molecules [18,19] and pesticides [20][21][22].…”