Biology subjects

Brillard, J.

Publications and source records attributed to Brillard, J..

3 recordsLinked to original sources

bioRxiv2026

Experimental evolution at high temperature in a Lepidopteran host of an entomopathogenic nematode and its associated microbiota

Entomopathogenic Nematodes (EPNs) have a great potential to control various insect crop pests, but their ability to perform their entire life-cycle in insects depends on environmental conditions. The insect killing ability of the endosymbiotic bacterial species (i.e., Xenorhabdus) located in the EPNs' gut (Steinernema) has been described for years. More recently, experimental data have suggested that other bacteria species of the nematode microbiota may also contribute to the parasitic success of the EPNs. EPNs and their associated bacteria should therefore be considered as holobionts. Global change, among its many predicted consequences, is expected to increase temperatures which may impair the parasitic success of these EPNs in the insect. Furthermore, higher environmental temperatures could modify the composition of the EPN-associated microbiota and could therefore also contribute to parasitic impairement. Using a S. carpocapsae strain originating from a French orchard, we investigated these hypotheses by experimentally evolving independent EPNs lineages in vivo in the lepidopteran species Galleria mellonella, at elevated and control temperatures. Several life-history traits of the evolved lineages were measured (insect killing ability, EPN emergence rate, EPN reproduction rate), and the bacterial microbiota of the evolved lineages was characterized by a metabarcoding approach. The EPNs' lineages evolved at higher temperature showed impaired emergence rate and their reproduction rate was lower, when compared to lineages evolved at control temperature. The bacterial microbiota composition of these lineages was modified, with particular enrichment in bacteria of the genera Alcaligenes and Pseudomonas. Our results provide new evidence that modification of the environment (here, the abiotic parameter temperature) during several successive generations can modify the parasitic success of EPNs, concomitantly to a change in the microbiota composition. A better understanding of the life-history traits of these EPNs should help improve the biocontrol efficiency in a context of global warming.

microbiology↗

bioRxiv2023

Evidence for increased fitness of a plant pathogen conferred by epigenetic variation

Adaptation is usually explained by adaptive genetic mutations that are transmitted from parents to offspring and become fixed in the adapted population. However, more and more studies show that genetic mutation analysis alone is not sufficient to fully explain the processes of adaptive evolution and report the existence of non-genetic (or epigenetic) inheritance and its significant role in the generation of adapted phenotypes. In the present work, we tested the hypothesis of the role of DNA methylation, a form of epigenetic modification, in adaptation of the plant pathogen Ralstonia solanacearum to the host plant during an experimental evolution. Using SMRT-seq technology, we analyzed the methylomes of 31 experimentally evolved clones that were obtained after serial passages on a given host plant during 300 generations, either on susceptible or tolerant hosts. Comparison with the methylome of the ancestral clone revealed between 12 and 21 differential methylated sites (DMSs) at the GTWWAC motif in the evolved clones. Gene expression analysis of the 39 genes targeted by these DMSs revealed limited correlation between differential methylation and differential gene expression. Only one gene showed a correlation, the RSp0338 gene encoding the EpsR regulator protein. The MSRE-qPCR (Methylation Sensitive Restriction Enzyme - qPCR) technology was used as an alternative approach to assess the methylation state of the DMSs found by SMRT-seq between the ancestral and evolved clones. This approach also found the two DMSs upstream of RSp0338. Using site-directed mutagenesis, we demonstrated the contribution of these two DMSs in host adaptation. As these DMSs appeared very quickly in the experimental evolution, we hypothesize that such fast epigenetic changes can allow rapid adaptation to the plant stem environment. To our knowledge, this is the first study showing a link between epigenetic variation and evolutionary adaptation to new environment.

evolutionary biology↗

bioRxiv2019

Photorhabdus 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.

microbiology↗