【报告题目1】 Exquisite architectures of surface appendages of marine microorganisms
【报告人】 吴龙飞 (Research director, Centre National de la Recherche Scientifique, France)
【报告题目2】Why keep the pressure to estimate prokaryotic activities?
【报告时间】 11月21日周四 上午10：00-11：30
【报告人】 Christian Tamburini (Research associate , Centre National de la Recherche Scientifique, France)
Bacteria produce diverse appendages on their outer surfaces. These extracellular structures, called pili, fimbriae, spinae, stocks or flagella are employed in attachment and invasion, biofilm formation, cell motility or nutrient uptake. Our studies have revealed two exquisite architectures of the marinebacterial surface appendages: spinae and flagella. Electron cryo-tomographyrevealed that the spinae of a marine bacterium Roseobacter spinae consist of a single proteolysis-resistant filament winding into a helical, hollow flared base that progressively changes to a cylinder with an overall view like the Eiffel Tower. Thermal treatmentripped the spinae into ribbons that were melted with prolonged heating. Differential scanning calorimetry, infrared spectroscopy and X-ray energy dispersive spectroscopy analyses suggest that the main component of the spinae is non-proteinous. Therefore, the spinae distinguish from other bacterial appendages in both the chemical composition and mechanism of assembly. Marine magnetotactic ovoid bacterium MO-1 is capable of swimming along the geomagnetic field lines by means of its two sheathed flagellar bundles at speed up to 300µm/s. By using electron microscopy we showed that, in each bundle, 6 individual flagella were organized in hexagon with a seventh in the middle. We identified 12 flagellin paralogs and 2 putative flagellins in the genome of MO-1. Using RT-PCR and q-PCR and nLC-ESI-MS/MS mass spectrometry analyses we found that all flagellin genes were transcribed and that twelve flagellin proteins are glycosylated and existed in multiple isoforms. These results show unprecedented complexity in the spatial organization and flagellin composition of the flagellar propeller. Such architecture is observed only for ovoid-coccoid, bilophotichously flagellated magnetotactic bacteria living in marine sediments, suggesting aspecies and environmental specificity. Taken together, these results imply that there are still many exquisite architectures of marine bacteria waiting to be discovered.
Hydrostatic pressure influences the physiology of organisms living at depth in the ocean, the most extensive habitat of the biosphere in terms of volume (1.3 x 1018 m3). The realm below 200 m, the dark ocean, is characterized not only by permanent darkness (insufficient light to support photosynthesis) but also by cold temperature(except for the Mediterranean, Red, and Sulu Seas), high inorganic nutrients, and low organic carbon concentration.
Recent discoveries challenge the paradigm that cycling of organic matter is slow in the deep sea and mediated by microbial food webs of static structure and function. Data showing spatial variation in prokaryotic abundance and activity support the hypothesis that deep-sea microorganisms respond dynamically to variations in organic matter input to the bathypelagic realm. Moreover, almost half of the total water column heterotrophic prokaryotic production takes place below the epipelagic layer. Compiled global budgets suggest that the estimate of metabolic activity in the dark pelagicocean exceeds the input of organic carbon. However, these conclusions are based mainly on measurements done at atmospheric pressure without taking into account pressure effects on natural prokaryotic assemblages.
The high-pressure sampler developed in our laboratory, fully adapted to usual Sea-Bird rosette carousel to take deep-sea samples will be presented. I will also present other high-pressure equipments useful to perform laboratory experiments (sinking particles simulation, strain culture studies…).
In this presentation, I will clarify, by reviewing literature data, the effect of hydrostatic pressure on prokaryotes living in the dark ocean and inform experimental design and the achievement of more accurate estimates of microbial activity in the deep ocean. Their potential capabilities to degrade complexcompounds as well as the chemolithoautrophy in the deep ocean represent examples of ways to explore deeper the role of deep-sea prokaryotes in the global cycles. Finally, I will also present link between physica l and environmental variables with biological activity (using bioluminescence as a proxy) in the Mediterranean deep-sea waters