Abstract
Simple SummaryEuropean Bark Beetle (Ips typographus) is a pest that affects dead and weakened spruce trees. Under certain environmental conditions, it has massive outbreaks, resulting in attacks of healthy trees, becoming a forest pest. It has been proposed that the bark beetle’s microbiome plays a key role in the insect’s ecology, providing nutrients, inhibiting pathogens, and degrading tree defense compounds, among other probable traits. During a study of bacterial associates from I. typographus, we isolated three strains identified as Pseudomonas from different beetle life stages. In this work, we aimed to reveal the taxonomic status of these bacterial strains and to sequence and annotate their genomes to mine possible traits related to a role within the bark beetle holobiont. Our study indicates that these bacteria constitute a new species for which the name of Pseudomonas typographi sp. nov. is proposed. Moreover, their genome analysis suggests different metabolic pathways possibly related to the beetle’s ecology. Finally, in vitro tests conclude the capability of these bacteria to inhibit beetle’s fungal pathogens. Altogether, these results suggest that P. typographi aids I. typographi nutrition and resistance to fungal pathogens. These findings might be of interest in the development of integrated methods for pest control.European Bark Beetle Ips typographus is a secondary pest that affects dead and weakened spruce trees (Picea genus). Under certain environmental conditions, it has massive outbreaks, resulting in the attacks of healthy trees, becoming a forest pest. It has been proposed that the bark beetle’s microbiome plays a key role in the insect’s ecology, providing nutrients, inhibiting pathogens, and degrading tree defense compounds, among other probable traits yet to be discovered. During a study of bacterial associates from I. typographus, we isolated three strains identified as Pseudomonas from different beetle life stages. A polyphasic taxonomical approach showed that they belong to a new species for which the name Pseudomonas typographi sp nov. is proposed. Genome sequences show their potential to hydrolyze wood compounds and synthesize several vitamins; screening for enzymes production was verified using PNP substrates. Assays in Petri dishes confirmed cellulose and xylan hydrolysis. Moreover, the genomes harbor genes encoding chitinases and gene clusters involved in the synthesis of secondary metabolites with antimicrobial potential. In vitro tests confirmed the capability of the three P. typographi strains to inhibit several Ips beetles’ pathogenic fungi. Altogether, these results suggest that P. typographi aids I. typographi nutrition and resistance to fungal pathogens.
Highlights
European bark beetle I. typographus is a secondary pest that affects mainly dead, stressed, and weakened spruce trees (Picea genus)
As a part of a broader work aiming to study bacteria associated to bark beetles, we isolated strains CA3AT, C2L11, and C2L12B, which, based on the nearly complete
HW001T was included as an outgroup (Figure 1). This analysis showed that strains CA3AT, C2L11, and C2L12B cluster together and aside of every closest Pseudomonas-type strain included in the analysis
Summary
European bark beetle I. typographus is a secondary pest that affects mainly dead, stressed, and weakened spruce trees (Picea genus). Its main life cycle occurs inside the inner bark of their host. Adult bark beetles perforate the external bark to reach the inner bark, where their life cycle will be developed. They excavate their own galleries, develop, and proceed through all the life stages (pupae, young adult, and adults). Almost all their life cycle develops inside the inner bark, which is mainly composed of cellulose, hemicellulose, and lignin [1,3,4]
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