Print PageThermal adaptations regulate the metabolic responses of microorganisms to changing temperature. Understanding community-level thermal adaptations should improve our understanding of the temporal dynamics of microbial community function at a range of temporal and spatial scales. In addition, such information could improve our ability to model the microbial contribution to ecosystem respiration. For example, the length of seasonal lags in community response to temperature could influence the Q10 of soil respiration. Any markers of thermal adaptation that can be derived from large-scale molecular profiling of microbial communities could provide insights into the climatic drivers of fungal community dynamics and ecosystem respiration. We explored the utility of phylogeny and secondary structure, specifically the %GC content of stem regions, of the ITS2 rRNA gene as indicators of thermal adaptation in fungi. Although explorations of rRNA in prokaryotes indicate that stem regions of rRNA are enriched in %GC with increasing temperature, this pattern has not been explored in fungi. The ITS2 region is widely used in high-resolution fungal community analyses, and has been the subject of tool development for secondary structure prediction. If thermal adaptation information can be extracted from the ITS2 region, simultaneous analysis of community composition and thermal adaptation could be achieved. We related phylogeny, known secondary structures (%GC) and thermal adaptation traits (maximum growth temperature) from the literature and our own databases.
Results/Conclusions
We found a strong phylogenetic signal in both thermal adaptation and GC content, with GC content in basal fungal lineages < Basidiomycota < Ascomycota, and significant variation among lineages within these taxonomic groups. Phylogenetic pattern in thermal adaptation was found at a range of taxonomic levels. The group with the highest %GC (Ascomycota) also had the most thermophilic species and the fewest psychrophilic species. However, without controlling for phylogeny stem %GC does not predict maximum growth temperature. We are exploring whether adaptation to osmotic stress could also influence base composition. Partitioning of phylogenetic, thermal and other drivers of ITS2 stem GC% will be necessary to discern a thermal adaptation signal in fungal community rDNA profiles. Directly relating phylogeny to thermal adaptations of cultured fungi may be a useful foundation for predicting thermal adaptations of uncultured fungi.
