Seasonal shifts in gut microbiota and cold tolerance metrics in a northern population of the eastern subterranean termite Reticulitermes flavipes

Eastern subterranean termites, Reticulitermes flavipes (Kollar), are widely distributed across North America where they are exposed to a broad range of environmental conditions. However, mechanisms to contend with variations in climatic conditions, are still not well understood. Wisconsin is a unique location to study mechanisms of cold tolerance as it represents the northern boundary for persistent R. flavipes populations. In this study, we evaluated seasonal shifts in cold tolerance using critical thermal minimum (CTmin) and supercooling point (SCP) data and examined how these data may correlate to changes in the microbial community of the termite gut at these same sampling dates. Results showed CTmin fluctuated seasonally, indicating cold acclimation. However, SCP increased with cold, meaning termites froze at higher temperatures. One possible explanation for this is an increase in uric acid content in the termite body at later collection dates, which may be serving as an ice nucleating agent. Principal coordinate analysis of the gut microbiota suggested seasonal shifts in microbial community composition and showed a strong correlation between the y-axis and SCP. In particular, Methanobrevibacter sp. (Euryarchaeota) seem to be associated with cold. Members of Methanobrevibacter are well-known for producing protective enzymes against oxidative stress which, combined with the antioxidant activity of uric acid, may be important in thermal tolerance. Further work is needed focusing on specific contributions of certain gut microbes, particularly their role in providing protection from oxidative stress associated with changes in environmental conditions and the importance of uric acid within this system.