Within gut physiochemical variation does not correspond to distinct resident fungal and bacterial communities in the tree-killing xylophage, Anolophora glabripennis

Authors: MASON, CHARLES - Pennsylvania State University; LONG, DAVID - Pennsylvania State University; MCCARTHY, ELIZABETH - Pennsylvania State University; ROSA, CHRISTINA - Pennsylvania State University; Scully, Erin; HOOVER, KELLI - Pennsylvania State University

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2017
Publication Date: 9/14/2017
Publication URL: https://handle.nal.usda.gov/10113/5822270
Citation: Mason, C.J., Long, D.C., McCarthy, E.M., Rosa, C., Scully, E.D., Hoover, K. 2017. Within gut physiochemical variation does not correspond to distinct resident fungal and bacterial communities in the tree-killing xylophage, Anolophora glabripennis. Journal of Insect Physiology. 102:27-35. http://dx.doi.org/10.1016/jinsphys.2017.08.003.
DOI: https://doi.org/10.1016/jinsphys.2017.08.003

Interpretive Summary: The Asian longhorned beetle (ALB) is a tree-killing insect that completes its entire development while feeding exclusively on woody tissue of its host trees, which is difficult to digest and contains low concentrations of essential nutrients. Fungi and bacteria housed in ALB’s gut can provide essential nutrients missing from woody tissue and contribute to digestion, but physiological conditions within the gut may be variable and impact the types of microbes present. Analysis of oxygen content and pH along the length of the gut revealed that while the pH and redox potential varied from 5.5 to 9 and high to low, respectively, from the middle to the lower regions of the gut t, and the oxygen content was consistently low throughout the entire gut. Despite the differences in pH and redox potential, the composition of the gut bacterial and fungal communities did not differ along the length of the gut. These differences in pH and redox potential in various regions of the gut possibly serve to accommodate different digestive processes occurring in different regions. The consistent gut microbial community throughout the gut indicates tolerance to a variety of environmental conditions and contribution to a variety of digestive processes. Understanding how gut microbes interact with ALB in different gut regions will allow us to better understand how they contribute to digestive physiology and how we can disrupt insect-microbe interactions to control this destructive pest.

Technical Abstract: Insect guts harbor diverse microbial assemblages that can be influenced by multiple factors, including gut physiology and interactions by the host with its environment. The Asian longhorned beetle (ALB; Anoplophora glabripennis) is an invasive tree–killing insect, which harbors a diverse consortium of fungal and bacterial gut associates that provision the beetle with nutrients and facilitate digestion of lignocellulose. The physiological conditions of the ALB gut and how these conditions may influence the microbial composition across gut regions are unknown. In this study, we measured oxygen tension, pH, and redox potential along the length of the ALB larval gut from two North American populations. We then analyzed and compared bacterial and fungal gut communities of ALB from these two populations within individual hosts along the length of the gut. The ALB midgut lumen was anoxic, with a pH gradient from 5.5 to 9, moving anterior to posterior. Redox potential was higher in the anterior midgut compared to posterior regions. We observed no differences in gut physiological conditions between the two populations. The two beetle populations harbored diverse assemblages of bacteria and fungi, which differed between the geographic locations. However, the composition of the ALB gut microbiota did not differ among gut regions despite physiological differences within a given host. Unlike other insect systems that have distinct gut compartmentalization and corresponding microbial assemblages, the ALB gut lacks such morphological modifications, which may explain why discrete regional microbial community structures were not found along the digestive system.