Khara, A. | Search bioRxiv

bioRxiv2025

Metagenomic characterisation of fungal communities associated with Scots pine bark beetles: mechanisms of selective antagonism and monoterpene tolerance

Bark beetle-associated fungi contribute to beetle nutrition, detoxification, and interactions with conifer hosts; however, their composition and function across development and environments remain poorly understood. We characterised fungal communities of two pine-feeding Ips bark beetles, I. sexdentatus and I. acuminatus, in larval, pupal, and adult stages, and in wild versus laboratory populations, using high-throughput ITS2 amplicon sequencing combined with qPCR and functional assays. Both beetles harboured a stable core mycobiome dominated by Kuraishia, Ogataea, Ophiostoma, Graphilbum and Cyberlindnera, while adults showed species-specific differences and wild beetles, especially I. acuminatus, exhibited greater diversity than laboratory populations. Beetles shared more taxa with unfed control wood than with gallery wood, indicating acquisition during feeding and concurrent restructuring of the wood mycobiome. Monoterpene bioassays on beetle-associated yeasts revealed that mixtures of -pinene, 3-carene and terpinolene suppressed growth more strongly than single compounds, suggesting synergistic inhibition. Yeasts selectively antagonised entomopathogenic fungi and expressed complementary cell-wall-lytic and digestive activities, consistent with combined roles in pathogen suppression and plant-polymer deconstruction. Our results show that Ips mycobiomes are conserved yet dynamic across life stages and environments, and emphasise the importance of multi-terpene and interaction assays for understanding bark beetle-fungus-conifer interactions. ImportanceOur study reveals that pine-feeding bark beetles co-evolved in close association with a stable core mycobiota that supports nutrient acquisition, detoxification, and chemical signalling, while additional fungal partners shift in response to beetle development, environment, and host context. By demonstrating higher mycobiome diversity in beetle larvae and wild populations, substantial overlap between beetle- and wood-associated fungi, differential sensitivity to monoterpene blends and selective antagonism of yeasts towards entomopathogenic fungi, our study unravels key ecological and mechanistic principles shaping beetle-fungus assemblages under conifers, paving the way for more in-depth functional investigations.

microbiology↗

bioRxiv2024

Comparative metagenomic study unveils bacterial communities and their putative involvement in ecological success of two pine-feeding Ips beetle holobionts

Climate change has recently boosted the severity and frequency of the pine bark beetle attacks. The bacterial community associated with these beetles acts as "hidden players", enhancing their ability to infest and thrive on defence-rich pine trees. There is limited understanding of the environmental acquisition of these hidden players and their life stage-specific association with different pine-feeding bark beetles. There is inadequate knowledge on novel bacterial introduction to pine trees after the beetle infestation. Hence, we conducted the first comparative bacterial metabarcoding study comprehensively revealing the bacterial communities in the pine trees before and after beetle feeding and in different life stages of two dominant pine-feeding bark beetles, namely Ips sexdentatus and Ips acuminatus. We also evaluated the bacterial association between wild and lab-bred beetles to measure the deviation due to inhabiting a controlled environment. Significant differences in bacterial amplicon sequence variance (ASVs) abundance existed among different life stages within and between the pine beetles. Such observations endorsed that the bark beetle life stage shaped bacterial assemblage. Furthermore, lab-bred and wild-collected adult beetles had distinct bacterial assemblages, implying that the breeding environment induced crucial changes. Alteration of pine wood bacteriome after beetle feeding is an intriguing observation in the present study, which demands further investigation. We validated the relative abundances of selected bacterial taxa estimated by metagenomic sequencing with quantitative PCR. Functional predictions revealed that these bacterial genera might execute conserved functions, aiding the ecological success of these beetles. Nevertheless, these findings shed new insights into bacterial associations and their putative metabolic roles in pine beetles under the influence of various drivers such as environment, host, and life stages and provide the foundation for future downstream functional investigations. ImportanceThe current understanding of bark beetle as holobiont is restricted. Most studies lack information on microbial community assembly in bark beetle microhabitats. No data comprehensively reveals the influence of lab breeding on pine beetle microbial associations. It is unknown if there is any adaptive convergence in beetle microbial assemblage due to feeding on the same host. Such information is essential to developing a bark beetle management strategy to restore forests from beetle-mediated damage. Our study shows that lab-breeding considerably influences beetle bacterial community assembly. We documented that beetle feeding alters bacteriome at the microhabitat level, and the beetle life stage shapes the bacterial associations. Nevertheless, our study revisited the bark beetle symbiosis under the influence of different drivers and revealed intriguing insight into bacterial community assembly, facilitating future functional studies.

microbiology↗