Linking bacterial diversity and biogeochemical cycling in a coastal planktonic community (Blanes Bay, NW Mediterranean)

GASOL, J. M.; ALONSO-SÁEZ, L.; BALAGUÉ, V.; CARDELÚS, C.; GÓMEZ-CORNASAU, L.; LEKUNBERRI, I.; PINHASSI, J.; SALA, M. M.; SCHAREK, R.; UNREIN, F.; VÁZQUEZ-DOMINGUEZ, E.; VILA-COSTA, M.; MASSANA, R.; SIMÓ, R.; PEDRÓS-ALIÓ, C.

Helsinki (Finlandia)

Simposio; SAME9, Symposium on Aquatic Microbial Ecology; 2005

 One of current goals of aquatic microbial ecologists is to identify bacteria that are key players in biogeochemical cycling. To that end, single-cell analysis techniques, such as autoradiography or flow cytometry, can be combined to the phylogenetic identification of the organisms. We show here the results of a seasonal study in which we calculate the contribution of different bacterial populations appearing in a coastal community to biogeochemical cycling. For example, summer communities were dominated by alpha-proteobacteria. Primary and bacterial productions were relatively low, and community respiration dominated over primary production. In July 2003, during a period of very stable warm weather, a free-living bacterial community was dominated (>30% of DAPI-positive cells) by Alteromonas, a representative of a group of cultivable gamma-proteobacteria which are fast-growing phylotypes commonly associated to transient changing water conditions. The appearance of this "bloom" of a particular bacterial group was associated to an extremely transparent water column, a high chlorophyll-specific primary production, high bacterial production, and a high percentage of active and actively-respiring bacteria, much above what is the normal summer situation. The bacterial community was limited by P but also by low-molecular weight organic molecules, such as DMSP. Using autoradiography associated to FISH, we computed the contribution of this single population to total community carbon and sulfur cycling, and compared it to other times of the year. We were able to associate values of carbon and sulfur cycling in a natural planktonic bacterial community to the presence of a dominant group of organisms.