Christopher Burot (CEM/MEB) will present his thesis in person and by videoconference on : Friday, March 18, 2022 at 9:30 am (Oceanomed Amphitheater)

On the following topic:

"Study of the degradation of ice algae and open water phytoplankton in the Arctic zone: impact of the stress state of the bacteria associated with this material on its preservation and contribution to sediments"

Director : Mr. JEAN-FRANCOIS RONTANI, RESEARCH DIRECTOR
Co-director: Mrs. PATRICIA BONIN, RESEARCH DIRECTOR

Abstract:

The Arctic Ocean and the perturbations of its functioning linked to global warming are a major concern of the world scientific community. At the base of the functioning of the Arctic Ocean is the primary production, provided by sympagic organisms called ice algae. In some Arctic regions, they can provide up to 60% of the total primary production. Given the relatively low degradation activity of this material by the bacterioplankton in these regions (between 25 and 80% of the bacterioplankton being dead or inactive) and the capacity of the sympagic material to fall rapidly to the sediments, the ice algae contribute strongly to the export of atmospheric carbon to the sea floor. The low degradation activity of bacterioplankton can be attributed to: (i) osmotic stress in hypersaline ice brine channels, (ii) chemical stress related to the production of bactericidal compounds by ice algae or (iii) photooxidative stress.

   The objective of this thesis is therefore to better understand the impact of these different stresses on the physiological state of bacteria associated with sympagic material and on the preservation of the latter along its fall to the sediments. The effect of haline and chemical stresses has been demonstrated through the analysis of numerous samples of particles in suspension, sedimentation or sediments collected during various sampling campaigns in the Canadian Arctic. These analyses have demonstrated the importance of haline stress on bacteria associated with sympagic algae, especially at the beginning of the melt cycle, which is the cause of a lower biodegradation activity by the associated bacteria. The importance of the stress related to the production of free fatty acids by ice algae, especially in case of strong irradiation of this material was also highlighted. Indeed, the quantities of free palmitoleic acid measured in our samples (up to 4.8 mg.L-1) seem to be at the origin of the high mortality (up to 75%) of associated bacteria observed in the ice and in the particles. The importance of photochemical stress on sympagic bacteria as well as the increased resistance of pigmented bacteria to this stress could also be demonstrated. These results may partly explain the high occurrence of pigmented bacteria in bacterioplankton communities at the end of phytoplankton blooms.

Key words: Ice algae, Associated bacteria, Photo-oxidative stress, Haline stress,