BUSCADOR RECOLECTA

MODIVUS Cruise (29GD20070917) carried out on the Research Vessel García del Cid in 2007, Dissolved organic matter serves as a source of energy for aquatic ecosystems. However, most of it is uncharacterized, and the processes that regulate its composition are practically unknown. The heterotrophic bacteria are responsible for the biotic mineralization of organic matter (OM) and therefore control their fate. But we do not know to what extent the mineralization is conditioned by the structure of the community of mineralizing microorganisms. The mineralization of MO by bacterial activity accounts for most of the CO2 production of the planktonic ecosystem, with which some of the most important functions of the ecosystems are directly influenced by the activity of the bacteria and the quality and types of OM , that probably interact. Three major objectives are at the base of the MODIVUS project: 1) the description of the sources of organic matter in a coastal ecosystem; 2) the relation of this organic matter, its composition and lability, with the structure of the communities of bacteria and 3) the relationship between the two components mentioned above (MO, bacterial diversity) and the functioning of the ecosystem (MO processing and respiration ). MODIVUS will combine in situ determinations with experimental approaches (disturbances in the laboratory and in nature). In situ (seasonal cycle in the coastal Mediterranean and small oceanographic campaign) the origin and degradability of the dissolved organic matter will be estimated (1), the composition and structure of the bacterial community is determined (2), and the functioning of the ecosystem in the processing of organic matter (lability, respiration, incorporation in the microbial trophic network) (3). The experiments are designed to determine the interactions between characteristics of dissolved organic matter and the structure of the bacterial community. Various types of experimental approaches will be used: microcosms, in situ incubations in dialysis bags, incubations with radiation manipulation. Our starting hypothesis is that it is possible to determine empirical relationships between the characteristics of the available organic matter, the structure of the bacterial community, and the functioning of the ecosystem with regard to the processing of that organic matter.water samples were collected during the MODIVUS cruise (17-27 September 2007) on board R/V García del Cid at three stations from coastal to open sea. Seawater (8 liters) was collected using Niskin bottles and was also prefiltered through 200-mm mesh net. A piece of 20-mm Nylon mesh was attached to the entrance tube cap of the filtration system and all environmental water samples were filtered first through a 3-mm pore-size polycarbonate filter (Poretics) and then through a 0.2-mm polycarbonate filter (Poretics) using a peristaltic pump (MasterFlex 7553-89 with cartridges Easy Load II 77200-62, Cole-Parmer Instrument Company) to collect the bacteria and picoeukaryotes. Filters were flash-frozen in liquid nitrogen and then stored at -80ºC until processed. Total RNA was extracted from the 0.2-mm polycarbonate filters