Biology subjects

Marsot, M.

Publications and source records attributed to Marsot, M..

3 recordsLinked to original sources

bioRxiv2019

Taxon appearance from extraction and amplification steps demonstrates the value of multiple controls in tick microbiome analysis

BackgroundThe development of high throughput sequencing technologies has substantially improved analysis of bacterial community diversity, composition, and functions. Over the last decade, high throughput sequencing has been used extensively to identify the diversity and composition of tick microbial communities. However, a growing number of studies are warning about the impact of contamination brought along the different steps of the analytical process, from DNA extraction to amplification. In low biomass samples, e.g. individual tick samples, these contaminants may represent a large part of the obtained sequences, and thus generate considerable errors in downstream analyses and in the interpretation of results. Most studies of tick microbiota either do not mention the inclusion of controls during the DNA extraction or amplification steps, or consider the lack of an electrophoresis signal as an absence of contamination. In this context, we aimed to assess the proportion of contaminant sequences resulting from these steps. We analyzed the microbiota of individual Ixodes ricinus ticks by including several categories of controls throughout the analytical process: crushing, DNA extraction, and DNA amplification.\n\nResultsControls yielded a significant number of sequences (1,126 to 13,198 mean sequences, depending on the control category). Some operational taxonomic units (OTUs) detected in these controls belong to genera reported in previous tick microbiota studies. In this study, these OTUs accounted for 50.9% of the total number of sequences in our samples, and were considered contaminants. Contamination levels (i.e. the percentage of sequences belonging to OTUs identified as contaminants) varied with tick stage and gender: 76.3% of nymphs and 75% of males demonstrated contamination over 50%, while most females (65.7%) had rates lower than 20%. Contamination mainly corresponded to OTUs detected in crushing and DNA extraction controls, highlighting the importance of carefully controlling these steps.\n\nConclusionHere, we showed that contaminant OTUs from extraction and amplification steps can represent more than half the total sequence yield in sequencing runs, and lead to unreliable results when characterizing tick microbial communities. We thus strongly advise the routine use of negative controls in tick microbiota studies, and more generally in studies involving low biomass samples.

microbiology↗

bioRxiv2019

The immunomodulatory effect of IrSPI, a tick salivary gland serine protease inhibitor involved in Ixodes ricinus tick feeding

Ticks are strict hematophagous arthropods and are the most important vectors of pathogens affecting both domestic and wild animals worldwide. Moreover, they are second only to mosquitoes as vectors of human pathogens. Hard tick feeding is a slow process--taking up to several days for repletion prior to detachment--and necessitates extended control over the host response. The success of the feeding process depends upon injection of saliva by tick, which not only controls host haemostasis and wound healing, but also subverts the host immune response to avoid tick rejection during this long-lasting process. In turn, the manipulation of the host immune response creates a favourable niche for the survival and propagation of diverse tick-borne pathogens transmitted during feeding. Here, we report on the molecular and biochemical features and functions of IrSPI, an Ixodes ricinus salivary serine protease inhibitor involved in blood meal acquisition. Our results show that IrSPI harbours the typical conformational fold of Kunitz type I serine protease inhibitors and that it functionally inhibits the elastase and, to a lesser extent, chymotrypsin. We also show that IrSPI is injected into the host during feeding. Crucially, we found that IrSPI has no impact on tissue factor pathway-induced coagulation, fibrinolysis, apoptosis, or angiogenesis, but a strong effect on immune cells. IrSPI affects antigen-presenting macrophages by hampering IL-5 production. In addition, IrSPI represses proliferation of mitogen-stimulated CD4+ cells. The inhibition of T cell proliferation was associated with marked reductions in pro-inflammatory cytokine secretion. Our study contributes valuable knowledge to tick-host interactions and provides insights that could be further exploited to design anti-tick vaccines targeting this immunomodulator implicated in successful I. ricinus tick feeding.\n\nAuthor summaryTicks are the most important vector influencing both human and animal health in Europe, where Ixodes ricinus is the most abundant tick species. Ticks feed on animal or human blood for an extended period, during which their saliva allows both feeding and pathogen transmission by interfering with native host responses. A better understanding of tick-host-pathogen interactions is central to the discovery of improved control methods. Within this context, we previously identified IrSPI as an I. ricinus salivary molecule implicated in both tick feeding and bacterial transmission. This serine protease inhibitor was almost characterised as an elastase inhibitor, and here, we show IrSPI overexpression in several tick organs--especially salivary glands--during blood feeding. We demonstrate that IrSPI is injected into the host through saliva, and despite having no impact on endothelial cell angiogenesis or apoptosis during blood feeding, we report an immunomodulatory role, whereby CD4+ T lymphocyte proliferation is repressed and where the cytokine secretion pattern of both splenocytes and macrophages is modified. Our study provides new insights into the complex armament developed by ticks to overcome the host response, and uncovers a potential vaccine target for disruption of feeding processes and pathogen transmission.

animal behavior and cognition↗

bioRxiv2019

A three-years assessment of Ixodes ricinus-borne pathogens in a French peri-urban forest

BackgroundIxodes ricinus is the predominant tick species in Europe and the primary pathogen vector for both humans and animals. These ticks are frequently involved in the transmission of Borrelia burgdorferi sensu lato, the causative agents of Lyme borreliosis. While much more is known about I. ricinus tick-borne pathogen composition, information about temporal tick-borne pathogen patterns remain scarce. These data are crucial for predicting seasonal/annual patterns which could improve understanding and prevent tick-borne diseases. MethodsWe examined tick-borne pathogen (TBPs) dynamics in I. ricinus collected monthly in a peri-urban forest over three consecutive years. In total, 998 nymphs were screened for 31 pathogenic species using high-throughput microfluidic real-time PCR. ResultsWe detected DNA from Anaplasma phagocytophilum (5.3%), Rickettsia helvetica (4.5%), Borrelia burgdorferi s.l. (3.7%), Borrelia miyamotoi (1.2%), Babesia venatorum (1.5%) and Rickettsia felis (0.1%). Among all analysed ticks, 15.9% were infected by at least one of these microorganisms, and 1.3% were co-infected. Co-infections with B. afzeli/B. garinii and B. garinii/B. spielmanii were significantly over-represented. Moreover, significant variations in seasonal and/or inter-annual prevalence were observed for several pathogens (R. helvetica, B. burgdorferi s.l., B. miyamotoi, and A. phagocytophilum). ConclusionsAnalysing TBPs prevalence in monthly sampled tick over three years allowed us to assess seasonal and inter-annual fluctuations of the prevalence of TBPs known to circulate in the sampled area, but also to punctually detect less common species. All these data emphasize that sporadic tick samplings are not sufficient to determine TBPs prevalence and that regular monitoring is necessary.

epidemiology↗