Role of the Photorhabdus Dam methyltransferase during interactions with its invertebrate hosts

Photorhabdus luminescens is an entomopathogenic bacterium found in symbiosis with the nematode Heterorhabditis. Dam DNA methylation is involved in the pathogenicity of many bacteria, including P. luminescens, whereas studies about the role of bacterial DNA methylation during symbiosis are scarce. The aim of this study was to determine the role of Dam DNA methylation in P. luminescens during the whole bacterial life cycle including during symbiosis with H. bacteriophora. We constructed a strain overexpressing dam by inserting an additional copy of the dam gene under the control of a constitutive promoter in the chromosome of P. luminescens and then achieved association between this recombinant strain and nematodes. The dam overexpressing strain was able to feed the nematode in vitro and in vivo similarly as a control strain, and to re-associate with Infective Juvenile (IJ) stages in the insect. No difference in the amount of emerging IJs from the cadaver was observed between the two strains. Compared to the nematode in symbiosis with the control strain, a significant increase in LT50 was observed during insect infestation with the nematode associated with the dam overexpressing strain. These results suggest that during the life cycle of P. luminescens, Dam is not involved the bacterial symbiosis with the nematode H. bacteriophora, but it contributes to the pathogenicity of the nemato-bacterial complex

The plant endosphere world – bacterial life within plants

The plant endosphere is colonized by complex microbial communities and microorganisms, which colonize the plant interior at least part of their lifetime and are termed endophytes. Their functions range from mutualism to pathogenicity. All plant organs and tissues are generally colonized by bacterial endophytes and their diversity and composition depend on the plant, the plant organ and its physiological conditions, the plant growth stage as well as on the environment. Plant‐associated microorganisms, and in particular endophytes, have lately received high attention, because of the increasing awareness of the importance of host‐associated microbiota for the functioning and performance of their host. Some endophyte functions are known from mostly lab assays, genome prediction and few metagenome analyses; however, we have limited understanding on in planta activities, particularly considering the diversity of micro‐environments and the dynamics of conditions. In our review, we present recent findings on endosphere environments, their physiological conditions and endophyte colonization. Furthermore, we discuss microbial functions, the interaction between endophytes and plants as well as methodological limitations of endophyte research. We also provide an outlook on needs of future research to improve our understanding on the role of microbiota colonizing the endosphere on plant traits and ecosystem functioning.CEnter of the study of Biodiversity in AmazoniaCOntinental To coastal Ecosystems: evolution, adaptability and governanceBiosurveillance Next-Gen des changements dans la structure et le fonctionnement des écosystème

Changes in rearing conditions rapidly modify gut microbiota structure in <em>Tenebrio molitor</em> larvae

The gut microbiota of multicellular organisms has been shown to play a key role in their host biology. In mammals, it has an invariant component, responsible for establishing a mutualistic relationship with the host. It also contains a dynamic fraction which facilitates adaptation in response to changes in the environment. These features have been well described in mammals, but little is known about microbiota stability or plasticity in insects. We assessed changes in microbiota composition and structure in a reared insect after a change in rearing conditions. We reared Tenebrio molitor (Coleoptera, Tenebrioninae) larvae for five days in soil samples from two river banks and analyzed their gut microbial communities by a metabarcoding technique, using the V3-V4 region of the 16S rRNA gene and the housekeeping gene gyrB. We found that soil-reared insects had a significantly more diverse microbiota than the control insects and that insects reared in soil from different sites had significantly different microbiota. We confirmed this trend by absolute quantification of the two mains fluctuating taxonomic groups: the Enterobacteriaceae family and the Pseudomonas genus, dominant in the soil-reared insects and in the control insects, respectively. Our results suggest the existence of a resident microbiota in T. molitor gut, but indicate that rearing changes can induce rapid and profound changes in the relative abundance of some of the members of this resident microbiota

Bacterial community profile after the lethal infection of Steinernema–Xenorhabdus pairs into soil-reared Tenebrio molitor larvae

The host microbiota may have an impact on pathogens. This is often studied in laboratory-reared hosts but rarely in individuals whose microbiota looks like that of wild animals. In this study, we modified the gut microbiota of the insect Tenebrio molitor by rearing larvae in soil sampled from the field. We showed by high throughput sequencing methods that this treatment modifies the gut microbiota so that it is more diversified than that of laboratory-reared insects, and closely resembled the one of soil-dwelling insects. To describe what the entomopathogenic bacterial symbiont Xenorhabdus (Enterobacteriaceae), vectored by the soil-dwelling nematode Steinernema, might experience in natural conditions, we studied the infestation of the soil-reared T. molitor larvae with three Steinernema–Xenorhabdus pairs. We performed the infestation at 18◦C, which delays the emergence of new infective juveniles (IJs), the soil-dwelling nematode forms, but which is a temperature compatible with natural infestation. We analyzed by high throughput sequencing methods the composition of the bacterial community within the insect cadavers before the first emergences of IJs. These bacterial communities were generally characterized by one or two non-symbiont taxa. Even for highly lethal Steinernema–Xenorhabdus pairs, the symbiont does not dominate the bacterial community within the insect cadaver

<em>Photorhabdus</em> Dam methyltransferase overexpression impairs virulence of the nemato-bacterial complex in insects

Photorhabdus luminescens is an entomopathogenic bacterium found in symbiosis with the nematode Heterorhabditis. Dam DNA methylation is involved in the pathogenicity of many bacteria, including P. luminescens, whereas studies about the role of bacterial DNA methylation during symbiosis are scarce. The aim of this study was to determine the role of Dam DNA methylation in P. luminescens symbiosis with H. bacteriophora. We constructed a strain overexpressing dam by inserting an additional copy of the dam gene under the control of a constitutive promoter in the chromosome of P. luminescens and then achieved association between this recombinant strain and nematodes. The dam overexpressing strain was able to feed the nematode in vitro and in vivo similarly as a control strain, and to re-associate with Infective Juvenile (IJ) stages in the insect. No difference in the amount of emerging IJs from the cadaver was observed between the two strains. Compared to the nematode in symbiosis with the control strain, a significant increase in LT50 was observed during insect infestation with the nematode associated with the dam overexpressing strain. These results suggest that the P. luminescens Dam plays a role in the pathogenicity of the nemato-bacterial complex

Microbial biomarkers of tree water status for next‐generation biomonitoring of forest ecosystems

International audienceNext-generation biomonitoring proposes to combine machine-learning algorithms with environmental DNA data to automate the monitoring of the Earth's major ecosystems. In the present study, we searched for molecular biomarkers of tree water status to develop next-generation biomonitoring of forest ecosystems. Because phyllosphere microbial communities respond to both tree physiology and climate change, we investigated whether environmental DNA data from tree phyllosphere could be used as molecular biomarkers of tree water status in forest ecosystems. Using an amplicon sequencing approach, we analysed phyllosphere microbial communities of four tree species (Quercus ilex, Quercus robur, Pinus pinaster and Betula pendula) in a fores

Project Group &amp;quot;AUV Payload Development and Deep-Sea

The general objective of EXOCET/D is to develop, implement and test specific instruments aimed at exploring, describing, quantifying and monitoring biodiversity in deep-sea fragmented habitats as well as at identifying links between community structure and environmental dynamics. Inboard experimental devices will complement the approach, enabling experiments on species physiology. The EXOCET/D working fields include: video and acoustic imagery, in situ analysis of physicochemical factors, quantitative sampling of macro- and microorganisms, in vivo experiments, integration of multidisciplinary data, implementation on European deep-submersibles and a final phase of technical and scientific validation