Dissolved organic matter released by two marine heterotrophic bacterial strains and its bioavailability for natural prokaryotic communities.

Marine heterotrophic prokaryotes (HP) play a key role in organic matter processing in the ocean; however, the view of HP as dissolved organic matter (DOM) sources remains underexplored. In this study, we quantified and optically characterized the DOM produced by two single marine bacterial strains. We then tested the availability of these DOM sources to in situ Mediterranean Sea HP communities.

Changes in bacterial community metabolism and composition during the degradation of dissolved organic matter from the jellyfish Aurelia aurita in a Mediterranean coastal lagoon.

Spatial increases and temporal shifts in outbreaks of gelatinous plankton have been observed over the past several decades in many estuarine and coastal ecosystems. The effects of these blooms on marine ecosystem functioning and particularly on the dynamics of the heterotrophic bacteria are still unclear. The response of the bacterial community from a Mediterranean coastal lagoon to the addition of dissolved organic matter (DOM) from the jellyfish Aurelia aurita, corresponding to an enrichment of dissolved organic carbon (DOC) by 1.

High contribution of SAR11 to microbial activity in the north west Mediterranean Sea.

We investigated the abundance and activity of SAR11 on a monthly time scale between January 2008 and October 2008 in the oligotrophic NW Mediterranean Sea. Applying MICRO-CARD-FISH, we observed that SAR11 had a large contribution to bulk abundance (37 ± 6% of DAPI-stained cells) and to bulk bacterial heterotrophic production (BHP), as estimated from leucine incorporation (55 ± 15% of DAPI-cells assimilating leucine) in surface waters (5 m) throughout the study period. SAR11 contributed also substantially to the assimilation of glucose, ATP, and a combination of amino acids (44 ± 17%, 37 ± 14%, and 43 ± 12% of DAPI cells assimilating these compounds, respectively), organic compounds that provide either single or combined sources of C, P, and N.

Impact of lower salinity waters on bacterial heterotrophic production and community structure in the offshore NW Mediterranean Sea.

We investigated the impact of water masses originating from freshwater input on bacterial heterotrophic metabolism and community structure at an offshore site in the oligotrophic NW Mediterranean Sea in 2007 and 2008. By combining 16S rRNA gene clone libraries and MICRO-CARD-FISH we determined the dominant operational taxonomic units (OTU) and their contribution to bulk abundance and activity in the presence of buoyant water masses characterized by lower salinity (LSW, < 37.9) and compared these with the winter and spring phytoplankton blooms.