Phages with tails (Caudovirales) belong to three families, among which Siphoviridae possess a non contractile tail terminated by a tail tip or a baseplate serving for phage adsorption on its host. While the mechanism of bacterial infection by the two other Caudovirales families has been well documented, much less is known concerning infection of gram+ by Siphoviridae. Our group aims at deciphering the mechanisms underlying infection of Lactococcus lactis by siphophages. L. lactis, a Gram+ bacterium, and its bacteriophages (siphoviridae, dsDNA), are a topic of economical and scientific importance. Lactococcus lactis infection by virulent phages is an economical problem impairing any industrial milk fermentation for cheese production, because virulent phages are ubiquitous within their process environments as well as within pasteurized milk. Besides, several hundreds of L. lactis phages have been isolated worldwide, each phage infecting specifically one or a few L. lactis strains. In a previous project, we have determined the crystal structures of the receptor binding proteins (RBPs) from lactococcal phages, p2 and TP901-1, because the first step of infection involves the specific interaction of the phage RBP with the saccharidic host receptor evenly distributed at the surface of cell walls. The RBPs are attached to a phage organelle, the baseplate, which orientates it properly for receptor recognition. We have determined the structures of the phages p2 and TP901-1 baseplates by EM and X-ray diffraction. These two organelles (1.1 and 1.9 MDa) harbour 18 and 54 sugar binding sites, respectively. We have shown that p2 baseplate changes conformation in the presence of Ca++, a cation strictly necessary for infection. The 3D knowledge of the components of the baseplates revealed that many of them possess conserved structures. In particular we had shown that a common protein forms a baseplate hub of most gram+ infecting siphophages. Furthermore, some of these structural features are shared with other phages (Myoviridae) or even with the bacterial type VI secretion system. The present projects aims at keeping the momentum acquired. We have enormously progressed in understanding the mechanism of host recognition, still, we do not understand how the recognition event generates a signal, which, transmitted along the tail, triggers the capsid’s portal protein opening and DNA release. A first possible mechanism involves conformational changes of the major tail proteins (MTPs) induced by the baseplate activation. It might then propagate along the tail up to the terminator, and finally trigger the portal opening. A second hypothesis is based on a bell-ringing mechanism. The central component of the tail, the tail measure protein (TMP), might be pulled by the baseplate movement, which in turn would act on the portal protein. The portal trigger mechanism is likely general among siphophages and extends thus the generality of our project. Deciphering the trigger mechanism requires approaches in several directions. We will first examine by electron microscopy (EM) the effect of the receptors on the complete phage, ie, the conformational changes of the baseplate and eventually of the tail before and after DNA release. A second approach will involve the production (in E.coli or L.lactis) of complexes larger than the baseplates, incorporating all the components of the baseplate and tail, as well as receptor saccharides. Indeed, the tail size will be decreased to a few hexameric rings of the MTPs by reducing the size of the TMP. These constructions will be examined jointly by cryoEM and X-ray diffraction, in order to determine which of the two above-described mechanism is most likely. The virologists will provide the phages and perform functional infection assays of putatively important mutants identified by structural studies. Our ultimate goal is to assemble sufficient data to present a realistic “film” of viral infection, up to DNA ejection.

The Horizon Europe project MobiHdic (New model organism for biotechnology: Haslea diatoms and the omic approaches) aims at developing a new model organism, the marine benthic diatom Haslea ostrearia, using interdisciplinary and multi-omic approaches, for fundamental research and industrial applications. The project MobiHdic will capitalize on the outcomes of the H2020 GHaNA project (The Genus Haslea, New marine resources for blue biotechnology and Aquaculture, grant agreement No 734708/GHaNA/H2020-MSCA-RISE-2016) (March 2017 – February 2021), which explored the biodiversity and characterized a new marine bioresource, the diatom genus Haslea, for applications mainly in bivalve aquaculture. The main outcomes of the GHaNA project are so far: - increased knowledge in the biodiversity and biogeography of the genus Haslea (new species identified) - draft genomes of different strains and species of blue and non-blue Haslea - better knowledge about the photobiology of blue Haslea - progress in the culture and production of blue Haslea in photobioreactors (PBR) at the lab scale - description of isoprenoid biosynthesis pathway in Haslea - new insights in marennine chemical nature (polysaccharides associated to a specific chromophore) - assessment of the antibacterial activities of marennine and application to bivalve models MobiHdic general objectives Capitalizing on these main achievements, the project MobiHdic will allow exploring new research avenues for which a long-lasting effort is needed and new expertise required, some of them being fundamental and others more applied-oriented. This is the rationale that underpins the MobiHdic project, the overall objective of which being to develop a new model of phytoplankton experimental organism, the diatom Haslea ostrearia, using interdisciplinary and multi-omic approaches for fundamental aspects and biotechnology and health applications. Expected outputs of the MobiHdic project will concern: - reference genome, genetics, epigenetics, stability / evolution of genomes - transcriptomics, proteomics, metabolomics in Haslea diatoms - environmental genomics and Haslea ecology - varietal selection, maintenance, improvement and characterization of strains - upscale of benthic algal production systems and development of downstream processes - biotechnology, transformation, molecular engineering, synthetic biology - identification of original biosynthesis pathways of marennine-like pigments and HBIs - high-value product applications in: o health and cosmetic industry (antiproliferative / antimicrobial compound, natural blue pigment) o food and feed (prebiotic- or probiotic-like compounds) o marennine-like pigments as sensitive element in electrochemical biosensors o new biosilica-based functionalized materials (e.g., nanoporous materials in solar panels) To fulfill these objectives, the consortium MobiHdic will gather all the required expertise in (1) biology and physiology of phytoplankton, (2) chemistry and physics applied to natural compounds, (3) molecular biology, multi-omics and bioinformatics, and (4) biotechnology applied to microalgae.

There is an urgent need to develop reliable and reproducible sensing technologies for in situ and continuous water monitoring for surface water and wastewaters. The AQUAE project will address this need by specifically developing dedicated chemical sensors that are versatile and adaptable enough to monitor priority substances and their degradation in a wide range of aquatic environments. Real-time monitoring of water quality using these chemical sensors will be performed in the real environment and at the point of discharge, which is necessary to prevent micropollution, define appropriate corrective actions for environmental remediation and decide when they should be undertaken (SCIRPE, BRGM, IFREMER with CEDRE). The AQUAE project will provide an attractive solution for real-time monitoring of nutrient concentration to control sustainable remediation processes such as phytoremediation (SCIRPE with DEEP INSA) and nutrient recovery treatment (Bioengine Laboratory, U. Laval, Canada). The development of chemical sensors for on-site detection will skillfully combine infrared photonics (IR) and electrochemical (EC) technology, both well mastered by the consortium (ISCR, KLEARIA, I.FOTON, BRGM & IFREMER). These two spectroscopic methods will be coupled in a portable device with a common microfluidic system for a fast, multivariate and in situ monitoring of organic contaminants. This hybrid prototype combining IR and EC sensors is oriented towards water pollution problems and wastewaters treatment by phytoremediation or nutrient recovery treatment. In addition to its fabrication for on-site use, a major challenge of the project is to overcome a new scientific barrier by designing and fabricating IR & EC sensors on a unique Lab-on-Chip. This AQUAE's LOC multifunctional sensors with an adapted microfluidic system will be designed to detect various priority substances (BTEX, PAH, pesticides, phthalate, drug residues and nitrates). Its efficiency will be tested at the laboratory scale for a first proof of concept. The detection concentrations in the AQUAE project for considered micropollutants will be at laboratory scale : BTEX and PAHs in case of vicinity of accidental pollution range from 50-150 µg/L, phthalate DEHP often in the range of 1-100 µg/L in wastewater and rain water, pesticides more than 5 µg/L in polluted sites for which the standard at 0.1 µg/L can be largely exceeded like in the north of France (metolachlor), non-steroidal anti-inflammatory drugs (diclofenac and ibuprofene) with tested range µg/L-mg/L. For nitrates detected by electrochemical sensor, we will consider the Nitrates Directive (91/676/EEC) which requires Member States to respect the quality standard not to be exceeded for the good status of groundwater (50 mg/L). The recommendation for discharges to water are about 15 mg/L of total nitrogen in the case of a treatment plant with a capacity of more than 600 kg/d. At the national level, the nitrate pollutant load of small treatment plants remains marginal. Reduction efforts must be concentrated on agricultural inputs especially in “vulnerable zones" where specific agricultural practices are imposed to limit the risks of pollution. In the AQUAE project, the sensors robustness will be demonstrated in the range 1-100 mg/L, at least with daily measurements to prevent any accidental event and with a t of 30 min to follow the denitrification process, in agreement with surface water analysis and industrial applications. The 0.05-1 mg/L range is a bonus for seawater analyses.