PROOF

SINPAS : SINking PArticle Simulation

( 18-Fév-2008 / cT/mpT)

SCIENTIFIC GOALS

Hypotheses:

1) Increase in hydrostatic pressure conditions alters bacterial mineralization rates and slows down the decomposition of particle during their fall throughout the water column. This affects (a) the quality of DOM released into the seawater, thus modifying the growth of pelagic bacteria, and (b) the dissolution rate of mineral ballasts (silicate, carbonate and dust). Dissolution of mineral ballast would affect the sinking rate of particles.

2) Hydrostatic pressure condition alters the species composition of prokaryotes communities associated with sinking particles. This succession in microbial communities alters biogeochemical processes exerted by prokaryotes on the particles. This affects mineralization processes throughout intermediate and deep-sea water masses, and the pelagic-benthos coupling, and thus the flux and the quality of organic inputs for intermediate, deep-sea and benthic microbial communities.

Objectives:

1) To quantify effects of increasing hydrostatic pressure on microbiological processes of organic matter mineralization (POC DOC transformation) and regeneration of biogenic elements (silicates, carbonates) within intermediate and deep-sea waters. These biogeochemical processes affect organic inputs throughout the intermediate and deep-sea water masses and the coupling between the pelagic zone and the benthos.

2) To determine effects of hydrostatic pressure on prokaryotic species composition ( Bacteria and Archaea ) using DGGE (or T-RFLP) and FISH during sinking simulation experiments and in "neutrally buoyant floc" (atmospheric pressure) experiments.

3) To study effects of hydrostatic pressure on the dynamics of prokaryotic community composition and activities. The microbial "black box" should not be regarded as homogeneous. Micro-FISH method breaks down this black box with fluorescent 16S rRNA probes and simultaneously determines DOM uptake by each prokaryotic subgroup.

SCIENTIFIC CONTEXT

Sinking particulate matter is the major vehicle for exporting carbon and energy from the sea surface to the intermediate and deep-sea waters until the final receptacle constituted by the sediments. During its transit towards the seafloor, most particulate organic carbon (POC) is returned to inorganic form. Attached bacteria play an important role in the degradation of aggregates, converting POC to dissolved organic carbon (DOC), bacterial carbon and carbon dioxide (CO2) through the preliminary step of ectoenzymatic hydrolysis Experiments devoted to the measurement of biodegradation rates of sinking particles are currently conducted under atmospheric pressure conditions.

We used a new experimental strategy to simulate the particle sinking through the water column. Our preliminary results show that the increase of hydrostatic pressure affects the bacterially-mediated biodegradation and biodissolution of sinking particles. Yet, metabolic activities of surface-produced bacteria attached on particles sinking through the whole water column decrease in the twilight zone, and then in the deep-sea water. Hence, thanks to the we propose, we will be able to better understand a major step of the functioning of the global ocean, and to better quantify the role of attached bacteria on the transformation POC to DOC and recycling of biogenic elements (as silicate and carbonate biominerals).

Molecular techniques based on culture-independent methods would permit us to better understand the role of heterotrophic bacteria in organic cycles and other biogeochemical processes. Whenever the metabolic potential of a community has been demonstrated, molecular techniques such as DGGE make it possible to know its structure without isolation. After DNA extraction of the community, PCR products of 16S rRNA V3-V5 gene fragments can be separated according to their electrophoretic mobility along a denaturating gradient. DGGE can sort DNA fragments of identical length but with different nucleotide sequences. DGGE can detect up to 95% of all possible single base substitutions among sequences of up to 1000 base pairs in length. After electrophoresis, major DGGE bands can be excised from the gel for subsequent phylogenic analysis or detected by genus probe after hybridization. However a number of studies has shown that bacteria attached to particles may be phylogenetically different from free-living bacteria.

This project consists of multidisciplinary experimental studies devoted to biogeochemical processes of interest for the modeling of mater and energy flows through the whole water column. Experimental data obtained using the a specific equipment allowing to simulate increase in pressure conditions during the sink of particles through the water column will be related to field data obtained from sediment traps, and analysis of organic and inorganic compound concentrations in the water column. So, results will greatly enhance the possibility to quantify and qualify the pelagos – benthos relationships.


SCIENTIFIC GOALS

	Hypotheses: 1) Increase in hydrostatic pressure conditions alters bacterial mineralization rates and slows down the decomposition of particle during their fall throughout the water column. This affects (a) the quality of DOM released into the seawater, thus modifying the growth of pelagic bacteria, and (b) the dissolution rate of mineral ballasts (silicate, carbonate and dust). Dissolution of mineral ballast would affect the sinking rate of particles. 2) Hydrostatic pressure condition alters the species composition of prokaryotes communities associated with sinking particles. This succession in microbial communities alters biogeochemical processes exerted by prokaryotes on the particles. This affects mineralization processes throughout intermediate and deep-sea water masses, and the pelagic-benthos coupling, and thus the flux and the quality of organic inputs for intermediate, deep-sea and benthic microbial communities. Objectives: 1) To quantify effects of increasing hydrostatic pressure on microbiological processes of organic matter mineralization (POC DOC transformation) and regeneration of biogenic elements (silicates, carbonates) within intermediate and deep-sea waters. These biogeochemical processes affect organic inputs throughout the intermediate and deep-sea water masses and the coupling between the pelagic zone and the benthos. 2) To determine effects of hydrostatic pressure on prokaryotic species composition ( Bacteria and Archaea ) using DGGE (or T-RFLP) and FISH during sinking simulation experiments and in "neutrally buoyant floc" (atmospheric pressure) experiments. 3) To study effects of hydrostatic pressure on the dynamics of prokaryotic community composition and activities. The microbial "black box" should not be regarded as homogeneous. Micro-FISH method breaks down this black box with fluorescent 16S rRNA probes and simultaneously determines DOM uptake by each prokaryotic subgroup.
SCIENTIFIC CONTEXT

	Sinking particulate matter is the major vehicle for exporting carbon and energy from the sea surface to the intermediate and deep-sea waters until the final receptacle constituted by the sediments. During its transit towards the seafloor, most particulate organic carbon (POC) is returned to inorganic form. Attached bacteria play an important role in the degradation of aggregates, converting POC to dissolved organic carbon (DOC), bacterial carbon and carbon dioxide (CO2) through the preliminary step of ectoenzymatic hydrolysis Experiments devoted to the measurement of biodegradation rates of sinking particles are currently conducted under atmospheric pressure conditions. We used a new experimental strategy to simulate the particle sinking through the water column. Our preliminary results show that the increase of hydrostatic pressure affects the bacterially-mediated biodegradation and biodissolution of sinking particles. Yet, metabolic activities of surface-produced bacteria attached on particles sinking through the whole water column decrease in the twilight zone, and then in the deep-sea water. Hence, thanks to the we propose, we will be able to better understand a major step of the functioning of the global ocean, and to better quantify the role of attached bacteria on the transformation POC to DOC and recycling of biogenic elements (as silicate and carbonate biominerals). Molecular techniques based on culture-independent methods would permit us to better understand the role of heterotrophic bacteria in organic cycles and other biogeochemical processes. Whenever the metabolic potential of a community has been demonstrated, molecular techniques such as DGGE make it possible to know its structure without isolation. After DNA extraction of the community, PCR products of 16S rRNA V3-V5 gene fragments can be separated according to their electrophoretic mobility along a denaturating gradient. DGGE can sort DNA fragments of identical length but with different nucleotide sequences. DGGE can detect up to 95% of all possible single base substitutions among sequences of up to 1000 base pairs in length. After electrophoresis, major DGGE bands can be excised from the gel for subsequent phylogenic analysis or detected by genus probe after hybridization. However a number of studies has shown that bacteria attached to particles may be phylogenetically different from free-living bacteria. This project consists of multidisciplinary experimental studies devoted to biogeochemical processes of interest for the modeling of mater and energy flows through the whole water column. Experimental data obtained using the a specific equipment allowing to simulate increase in pressure conditions during the sink of particles through the water column will be related to field data obtained from sediment traps, and analysis of organic and inorganic compound concentrations in the water column. So, results will greatly enhance the possibility to quantify and qualify the pelagos – benthos relationships.