Isabelle Billy

Digenean trematodes-marine mollusc relationships: a stable isotope study.

The stable carbon and nitrogen isotopic composition of digenean trematode parasites and their marine mollusc hosts was investigated to describe the potential influence of parasites on their host and its different tissues, and to obtain further insight into their trophic relationships. Four parasite-host systems were studied: Labratrema minimus-Cerastoderma edule, Monorchis parvus-C. edule, Lepocreadiidae parasites-Nassarius reticulatus and Zoogonidae parasites-N. reticulatus. Among the 4 sampling occasions reported here and corresponding to the 4 parasite-host systems, isotopic shifts from pathologic (i.e. linked to disturbances in host metabolism) and mass-balance (i.e. linked to significant differences between host and parasite isotopic signatures) origins were observed only once. Both corresponded to delta 13C measurements of the L. minimus-C. edule system when the infestation load (percentage parasite dry weight compared to total flesh dry weight) was highest (9 to 25%, mean = 16%) over the sampling period. Overall, measurements indicate that digenean trematode parasitism induced low or no shifts in isotopic signatures of C. edule and N. reticulatus tissues. The 2 endoparasites L. minimus and M. parvus appeared to be slightly depleted in 13C compared to C. edule digestive gland and gonads, which were the most parasitized tissues. In contrast, no fractionation or low 15N trophic enrichments occurred in the parasites. These results highly contrast with the classical trophic enrichment reported in prey-predator systems but are in agreement with the scarce literature regarding other parasite-host systems. Our results indicate that (1) digenean trematodes mainly feed on digestive glands (the cockle tissue with which they are mainly associated) with a possible slight preference for lipids, and (2) fractionation due to parasite metabolism should be low due to abbreviated metabolic pathways and/or slight loss of materials through excretion, tegument diffusion and respiration.

Sonochemical Disproportionation of Carbon Monoxide in Water: Evidence for Treanor Effect during Multibubble Cavitation

Eighty years after the discovery of ultrasound-induced chemical processes, known as sonochemistry, it remains a subject of extensive research. It is generally accepted that sonochemistry arises from acoustic cavitation, which is the nucleation, growth, and implosive collapse of microbubbles in liquids subjected to ultrasonic waves. Nevertheless, debate still continues over the origin of extreme conditions created by the bubble collapse. Usually the sonochemical reactions are interpreted according to Flynn s “thermal” hypothesis presuming adiabatic or quasi-adiabatic transient heating of gases and vapours inside the cavitating bubble. However, the recent observation of light emission from positively charged O2 + species during single-bubble collapse in H2SO4 provided evidence for nonthermal plasma formation inside the bubble. The relationship between the mechanisms of single-bubble and multibubble cavitations is still not clear. Recent studies of multibubble sonoluminescence in H2SO4 and water revealed some similarities in the origin of both kinds of processes. 6] In this view thermal equilibration during the cavitation event remains an important question that is not yet resolved. Herein, we report the first “chemical” evidence for nonequilibrium molecule vibrational excitation occurring during multibubble cavitation. We studied the ultrasonically driven disproportionation of carbon monoxide (DCO) in water saturated with a CO/Ar gas mixture. To our knowledge, this reaction had never been studied under ultrasonic irradiation. By contrast, the plasma– chemical DCO reaction in the gas phase has been a very active topic of research as working media for CO lasers and as a promising method for carbon isotope separation. According to published results, the strongly endothermic DCO reaction (DH = 5.5 eVmol , Ea = 6 eVmol ) can be significantly accelerated by the vibrational excitation of CO molecules. The population of highly vibrational states CO*(nn), n 40, occurs through an anharmonic vibrationto-vibration pumping mechanism (V–V), known as the Treanor effect. This approach produces nonthermal plasma far from the thermodynamic equilibrium with a vibrational temperature (Tv) of CO molecules much higher than their translational (T0) or rotational (TR) temperatures. An experimental illustration of the Treanor V–V pumping is a kinetic isotope effect (KIE) during DCO in nonequilibrium plasma. The coefficient of isotopic selectivity (a) for vibrationally excited isotopes can be expressed by Equation (1), where Dw w 1⁄4 w2 w1 w2 is the relative defect of resonance.