Biology subjects

Deziel, E.

Publications and source records attributed to Deziel, E..

4 recordsLinked to original sources

bioRxiv2018

The symbiotic complex of Dendroctonus simplex: implications in the beetle attack and its life cycle

The eastern larch beetle (Dendroctonus simplex Le Conte) is recognized as a serious destructive forest pest in the upper part of North America. Under epidemic conditions, this beetle can attack healthy trees, causing severe damages to larch stands. Dendroctonus species are considered as holobionts, as they engage in multipartite interactions with microorganisms, such as bacteria, filamentous fungi, and yeasts, which are implicated in physiological processes of the insect, such as nutrition. They also play a key role in the beetles attack, as they are responsible for the detoxification of the subcortical environment and weaken the trees defense mechanisms. The eastern larch beetle is associated with bacteria and fungi, but their implication in the success of the beetle remains unknown. Here, we investigated the bacterial and fungal microbiota of this beetle pest throughout its ontogeny (pioneer adults, larvae and pupae) by high-throughput sequencing. A successional microbial assemblage was identified throughout the beetle developmental stages, reflecting the beetles requirements. These results indicate that a symbiotic association between the eastern larch beetle and some of these microorganisms takes place and that this D. simplex symbiotic complex is helping the insect to colonize its host tree and survive the conditions encountered.

ecology↗

bioRxiv2017

Fungal communities associated with the eastern larch beetle: diversity and variation within developmental stages

Bacterial and fungal communities associated with bark beetles, especially some Dendroctonus species, mediate challenging aspects of the subcortical habitat for their hosts. Filamentous fungi and yeasts are important in various metabolic processes of certain bark beetles, with involvement in nutrition, protection and detoxification of plant defense compounds. The eastern larch beetle, Dendroctonus simplex, is recognized as a serious forest pest in the upper part of North America. Although D. simplex is well studied, the fungal communities and their ecological role remain to be investigated. Here, using 18S rRNA gene pyrosequencing, we provide a comprehensive overview of the yeasts and filamentous fungi associated with the eastern larch beetle and compare fungal communities between different developmental stages and microenvironments. Fungal mycobiome associated with the galleries was also investigated. Our study has unveiled an unexpected fungal diversity associated with the developmental stages. Significant differences in species richness between the developmental stages were determined. Yeasts were found to be predominant in the adult and larval stages, whereas filamentous fungi were most prevalent in the pupae. Our results indicate a possible implication of yeasts in the eastern larch beetle nutrition.

microbiology↗

bioRxiv2017

Two rsaM homologues encode central regulatory elements modulating quorum sensing expression in Burkholderia thailandensis

The bacterium Burkholderia thailandensis possesses three conserved N-acyl-L-homoserine lactone (AHL) quorum sensing (QS) systems designated BtaI1/BtaR1 (QS-1), BtaI2/BtaR2 (QS-2), and BtaI3/BtaR3 (QS-3). These QS-systems are associated with the biosynthesis of N-octanoyl-homoserine lactone (C8-HSL), N-3-hydroxy-decanoyl-homoserine lactone (3OHC10-HSL), as well as N-3-hydroxy-octanoyl-homoserine lactone (3OHC8-HSL), which are produced by the LuxI-type synthase BtaI1, BtaI2, and BtaI3, and modulated by the LuxR-type transcriptional regulators BtaR1, BtaR2, and BtaR3. Both btaR1/btaI1 and btaR2/btaI2 gene clusters contain an additional gene that is conserved in the Burkholderia genus, homologous to a gene coding for the negative AHL biosynthesis modulatory protein RsaM originally identified in the phytopathogen Pseudomonas fuscovaginae, and hence designated rsaM1 and rsaM2. We have characterized the function of these two rsaM homologues and demonstrated their involvement in the regulation of AHLs biosynthesis in B. thailandensis strain E264. We measured the production of C8-HSL, 3OHC10-HSL, and 3OHC8-HSL by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in the wild-type strain and in the rsaM1- and rsaM2- mutants, and monitored the transcription of btaI1, btaI2, and btaI3 using chromosomal mini-CTX-lux transcriptional reporters. The expression of btaR1, btaR2, and btaR3 was also measured by quantitative everse-transcription PCR (qRT-PCR). We demonstrate that the QS-1 system is repressed by RsaM1, whereas RsaM2 principally represses the QS-2 system. We also found that both rsaM1 and rsaM2 are QS-controlled, as well as negatively auto-regulated. We conclude that RsaM1 and RsaM2 are an integral part of the QS modulatory circuitry of B. thailandensis, and play a major role in the hierarchical and homeostatic organization of the QS-1, QS-2, and QS-3 systems.\n\nImportanceQuorum sensing (QS) is a global regulatory mechanism of genes expression depending on bacterial density. QS is commonly involved in the coordination of genes expression associated with the establishment of host-pathogen interactions and acclimatization to the environment. We present the functional characterization of the two rsaM homologues designated rsaM1 and rsaM2 in the regulation of the multiple QS systems coexisting in the non-pathogenic bacterium Burkholderia thailandensis, widely used as a model system for the study of the pathogen Burkholderia pseudomallei. We found that inactivation of these rsaM homologues, which are clustered with the other QS genes, profoundly affects the QS regulatory circuity of B. thailandensis. It is proposed that these genes code for QS repressors and we conclude that they constitute essential regulatory components of the QS modulatory network of B. thailandensis, and provide additional layers of regulation to modulate the expression of QS-controlled genes, including those encoding virulence/survival factors and linked to environmental adaptation in B. pseudomallei.

microbiology↗

bioRxiv2017

The complex quorum sensing circuitry of Burkholderia thailandensis is both hierarchically and homeostatically organized

The genome of the bacterium Burkholderia thailandensis encodes for three complete LuxI/LuxR-type quorum sensing (QS) systems: BtaI1/BtaR1 (QS-1), BtaI2/BtaR2 (QS-2), and BtaI3/BtaR3 (QS-3). The LuxR-type transcriptional regulators BtaR1, BtaR2, and BtaR3 modulate the expression of target genes in association with various N-acyl-L-homoserine lactones (AHLs) as signaling molecules produced by the LuxI-type synthases BtaI1, BtaI2, and BtaI3. We have systematically dissected the complex QS circuitry of B. thailandensis strain E264. Direct quantification of octanoyl-homoserine lactone (C8-HSL), N-3-hydroxy-decanoyl-homoserine lactone (3OHC10-HSL), and N-3-hydroxy-octanoyl-homoserine lactone (3OHC8-HSL), the primary AHLs produced by this bacterium, was performed in the wild-type strain and in QS deletion mutants. This was compared to the expression of btaI1, btaI2, and btaI3 using chromosomal mini-CTX-lux transcriptional reporters. Furthermore, transcription of btaR1, btaR2, and btaR3 was monitored by quantitative reverse-transcription PCR (qRT-PCR). We observed that C8-HSL, 3OHC10-HSL, and 3OHC8-HSL are differentially produced over time during bacterial growth and correlate with the btaI1, btaI2, and btaI3 genes expression profiles, revealing a sequential activation of the corresponding QS systems. Moreover, transcription of the btaR1, btaR2, and btaR3 genes is modulated by AHLs, showing that their regulation depend on themselves, and on other systems. We conclude that the three QS systems in B. thailandensis are interdependent, suggesting that they cooperate dynamically and function in a concerted manner in modulating the expression of QS target genes through a sequential regulatory network.\n\nImportanceQuorum sensing (QS) is a widespread bacterial communication system coordinating the expression of specific genes in a cell density-dependent manner and allowing bacteria to synchronize their activities and to function as multicellular communities. QS plays a crucial role in bacterial pathogenicity by regulating the expression of a wide spectrum of virulence/survival factors and is essential to environmental adaptation. The results presented here demonstrate that the multiple QS systems coexisting in the bacterium Burkholderia thailandensis, considered as the avirulent version of the human pathogen Burkholderia pseudomallei and thus commonly used as an alternative study model, are hierarchically and homeostatically organized. We found these QS systems finely integrated into a complex regulatory network, including transcriptional and post-transcriptional interactions, and further incorporating growth stages and temporal expression. These results provide a unique, comprehensive illustration of a sophisticated QS network and will contribute to a better comprehension of the regulatory mechanisms that can be involved in the expression of QS-controlled genes, in particular those associated with the establishment of host-pathogen interactions and acclimatization to the environment.

microbiology↗