(1st Place) The plant-cell-wall degraders and the core microbial community from the digestive tracts of the coconut rhinoceros beetle (Oryctes rhinoceros; Coleoptera: Scarabaeidae)

Coconut rhinoceros beetle (CRB, Oryctes rhinoceros) is a serious pest on palm trees that can digest woody plant tissues that many insects cannot. This study sought to identify how this diet is digested. Chemical assays of CRB intestinal tissues suggested the presence of enzymes that can break down cellulose and hemicellulose. These were hypothesized to be produced by intestinal microbes, since expression tests found that the endogenous CRB cellulase is inactive. The apparent hindgut swelling in CRB larvae suggests that major fermentation processes occur there. Tree-like structures on the hindgut inner lining were observed with stereomicroscopy. Scanning electron microscopy revealed that these structures are covered in a conspicuous biofilm comprised of possibly symbiotic bacteria. To investigate the composition of CRB’s hindgut microbiome and find the plant-cell wall-degraders, 16S sequencing was used to study the samples around Taiwan. The class Clostridia was dominant in most samples. Within this class, Papillibacter cinnamivorans and Christensenella massiliensis were identified as part of the core microbiome. Whole metagenome sequencing and the CRB transcriptome further provided a detailed profile of all carbohydrate active enzymes (CAZymes) from the CRB holobiont. Most CAZymes, especially lignocellulose degrading enzymes (LDMs), are derived from the microbiome. Phylogenetic reconstruction indicates the majority of LDM providers are Clostridia as well. In summary, this study identified a core microbiome group producing lignocellulolytic enzymes for CRB that may enable their survival on wood, can possibly be targeted as means of pest management and control, or could be used for biotechnological and industrial purposes.