Gut Microbiota of Ostrinia Nubilalis Larvae Degrade Maize Cellulose

BackgroundWhile most insects rely on gut bacteria to digest cellulose and produce sugars or fatty acids that are then available to the host, this has been disputed in Lepidopteran larvae due to their simple gut morphology and rapid digestive throughput. The European corn borer (ECB), Ostrinia nubilalis (Hübner), is a devastating pest that feeds the lignocellulose-rich tissues of maize plants. However, the potential role of ECB gut microbes in degrading maize cellulose remains unexplored. Here, we investigate the gut microbiota of ECB fed with different diets and the potential function of their gut bacteria in maize lignocellulose degradation.ResultsThe diversity and composition of gut bacterial communities varied dramatically between the ECB larva fed with artificial diets (ECB-D) and maize plants (ECB-M). Draft genomes of the bacterial isolates from ECB-D and ECB-M show that the principal degraders of cellulose mainly belonged to Firmicutes or Proteobacteria and were primarily found in the midgut. The bacterial isolates contained genes encoding various carbohydrate-active enzymes (CAZyme). Furthermore, scanning electron microscopy (SEM) revealed significant breakdown of lignocellulose in maize treated by the two bacterial isolates for nine days in vitro. Cellulose content in maize particles treated with BI-M were significantly lower than those treated with BI-D or the control (Kruskal–Wallis test: Χ2 = 6.72, df = 2; P = 0.0259). Metabolomic analyses reveal that maize particles treated by two bacterial isolates generate distinctive metabolomic profiles, with enrichment for different monosaccharides and amino acids.ConclusionThe results indicated that the diet of the host impacts the composition and the function of its gut microbiota, and that ECB exploits specific gut microbes to digest maize lignocellulose with distinctive products. Our study provides valuable microbiota resources for lignocellulose bioconversion.