Master of Science / Department of Grain Science and Industry / Bhadriraju Subramanyam / Hulya Dogan / Stored-product insects and stored products from feed mills and swine farms contain antibiotic and potentially virulent Enterococcus faecalis, Enterococcus faecium, Enterococcus casseliflavus, Enterococcus gallinarum, and Enterococcus hirae. Stored-product insects can serve as potential vectors of these enterococci which possess antibiotic resistance genes that can be spread by horizontal transfer to more serious human pathogens. In the present study, the species and concentration of enterococci from adults and larvae of key stored-product insects and insect diets and their antibiotic resistance profile were characterized. Adults of five species out of the 15 stored-product insects were tested positive for enterococci, and these included Callosobruchus maculatus (F.), Sitophilus granarius (L.), Stegobium paniceum (L.), Lasioderma serricorne (F.), and Sitophilus zeamais Motschulsky. Three enterococcal species (E. casseliflavus, E. faecalis, and E. faecium) were found in 53 to 97% of the 30 adults screened for each insect species, and the enterococcal concentrations ranged from 1.4 x 10³ to 3.1 x 10⁶ CFU/adult. About 10 to 100% of the mature larvae of the respective five insect species had these three enterococcal species with concentrations ranging from 0.3 x 10¹ to 1.4 x 10⁵ CFU/larvae. Only three of the eight insect diets screened had the same three enterococci species in addition to E. gallinarum and E. hirae at concentrations of 0.2 x 10¹ to 5.9 x 10³ CFU/g. The greatest enterococcal concentration was found in C. maculatus adults but not in their larvae or diet (cowpeas). In C. maculatus during a nine-day period after adult eclosion, the enterococcal concentrations increased exponentially from 0.6 x 10¹ to a maximum of 4.1 x 10⁷ CFU/adult. Enterococci were detected in the fecal material of C. maculatus during a four-day period with a maximum concentration of 3.3 x 10³ CFU/adult on the fourth day. A total of 298 enterococcal isolates from adults, larvae, and diets were represented by E. faecalis (51.7% of the total), E. faecium (19.1%), E. casseliflavus (18.8%), E. gallinarum (5.7%), and E. hirae (4.7%). Enterococci were phenotypically resistant to quinupristin (51.3% of the total), erythromycin (38.9%), tetracycline (30.1%), enrofloxacin (29.2%), doxycycline (11.5%), and tigecycline (2.7%). All isolates were susceptible to ampicillin and vancomycin.

The eutrophication of the Southern Bight of the North Sea has been benefitting to the prymnesiophyte Phaeocystis globosa (P. globosa). This species is a known high dimethylsulfoniopropionate (DMSP) producer whose bloom accounts for 95% of spring phytoplankton biomass. An increase in DMS(P) and its oxidation product dimethylsulfoxide (DMSO) cellular contents have been frequently observed in cellular stress conditions. To test this, we have first analysed the natural distribution of DMS(P,O) cellular contents in the North Sea. Secondly, we have measured DMS(P,O) cellular contents in monospecific cultures of several key species of the North Sea and their responses to salinity variations. Our main working hypothesis is that DMSP acts as an osmoregulator and/or as an antioxidant, depending on the species. The DMS(P,O) annual cycle in the Southern Bight of the North Sea revealed a seasonality linked to the spring phytoplankton communities succession: (1) colonial diatoms (reappearing in autumn), (2) Chaetoceros spp. (3) P. globosa, (4) large-size summer diatoms (mainly Guinardia spp.), and (5) dinoflagellates. Spatial gradients of DMS(P) were related to those of phytoplankton biomass, itself related to the inputs of nutrients from the Scheldt estuary. It also discharges suspended matter in which DMSO may have been produced by anaerobic oxidation of DMS. Laboratory measurements confirmed a large variability in DMSP cellular contents between the six studied diatoms (Nitzschia closterium, Skeletonema costatum, Thalassiosira rotula, Chaetoceros socialis, Chaetoceros debilis, and Guinardia delicatula), low producers in comparison with P. globosa and even more with Heterocapsa triquetra (Dinoflagellate). In particular, communities 2 and 4 have lower DMSP cellular contents than community 1 (N. closterium, S. costatum and T. rotula). Senescence induces a decrease in DMSP/DMSO suggesting an oxidative stress caused by nutrients and/or light limitation in DMSP producers. In S. costatum, DMSP seems to play an osmoregulatory role and is oxidised into DMSO in hyposaline conditions. In P. globosa and H. triquetra, an oxidative stress appears in hypo- and hypersaline conditions diverging from their salinity optimum. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Le géothermomètre Δ47 est basé sur la relation entre l’abondance des liaisons 13C–18O des carbonates et la température de calcification. Ce proxy contourne potentiellement les limites des autres thermomètres (δ18O, Mg/Ca) pour reconstruire les paléo-températures des océans, expliquant son développement exponentiel depuis dix ans. Cette thèse teste pour la première fois le potentiel et les limites de la thermométrie Δ47 sur les coccolithes, des nannofossiles calcaires produits par des organismes calcifiants dans la zone photique. Ces biominéraux calcitiques et ubiquistes constituent une part importante de l’archive sédimentaire. Des cultures in vitro nous ont permis d’établir que trois espèces de coccolithes actuelles enregistrent la même relation Δ47 – T que la calcite inorganique, alors qu'elles présentent de très larges effets vitaux en δ18O (±5‰). Nous concluons que ces espèces de coccolithes d'importance géologique ne présentent pas d’effets vitaux en Δ47. Nous avons ensuite appliqué le Δ47 à l’étude des sédiments enregistrant l’événement d’anoxie océanique du Toarcien (–183 Ma) au cours duquel les reconstructions de températures restent encore ambigües, notamment du fait de la méconnaissance de la composition isotopique en oxygène de l’eau de mer. Sur la base des données Δ47 acquises, nous proposons des températures élevées (de l’ordre de 36°C), mais restant relativement stables sur l'intervalle d'étude. En couplant ces températures aux données de δ18O des carbonates, nous suggérons une variation importante du δ18O de l'eau de mer dans le Bassin de Paris lors de la mise en place des faciès black shales. Enfin, sur des sédiments pélagiques subactuels, l’une des espèces étudiées présente des déséquilibres isotopiques en Δ47 non observés en culture et explicables par d’autres paramètres environnementaux comme l’intensité lumineuse. Cette thèse illustre le potentiel du thermomètre Δ47 des coccolithes en différents contextes, ouvrant un vaste champ d’application de reconstruction des paléo-environnements sur le Méso-Cénozoïque / The Δ47 geothermometer relies on the relationship between the 13C–18O abundance in carbonateand temperature of calcification. This proxy has the potential to overcome limitations of other thermometers(δ18O, Mg/Ca) to reconstruct oceanic paleotemperatures. This thesis evaluates for the first time the potentialand the limitations of the Δ47 thermometry of the coccoliths, the calcareous nannofossils produced byorganisms calcifying in the photic zone. These calcitic and ubiquitous biominerals represent an importantpart of the sedimentary archive. In vitro cultures allow us to establish that three modern coccoliths speciesrecord the same Δ47–T relation than inorganic calcite, although exhibiting substantial δ18O vital effects(±5‰). We conclude that these coccoliths species do not present any Δ47 vital effect. We subsequentlyapplied the Δ47 proxy to sediments from the Toarcian oceanic anoxic events (–183 Ma) during which thetemperatures reconstructions are still elusive, mainly due to the unknown oxygen isotopic composition ofseawater. On the basis of our Δ47 data, we infer relatively high, yet steady temperatures (around 36°C) duringthe examined interval. By combining these Δ47-derived temperatures to carbonate δ18O data, we can suggestdrastic change in the seawater δ18O composition in the Paris Basin at the onset of black shale deposition. Acore top calibration of Δ47 of coccoliths revealed that one of the studied cultured species exhibits Δ47disequilibrium that is accountable by other environmental parameters, such as light irradiance in the naturalenvironment. Thus, this thesis illustrates the potential of the coccolith Δ47 thermometer in different settings,opening a wide range of application to reconstruct the palaeoenvironments over the Meso-Cenozoic Eras