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1.  Short-term responses of unicellular planktonic eukaryotes to increases in temperature and UVB radiation 
BMC Microbiology  2012;12:202.
Small size eukaryotes play a fundamental role in the functioning of coastal ecosystems, however, the way in which these micro-organisms respond to combined effects of water temperature, UVB radiations (UVBR) and nutrient availability is still poorly investigated.
We coupled molecular tools (18S rRNA gene sequencing and fingerprinting) with microscope-based identification and counting to experimentally investigate the short-term responses of small eukaryotes (<6 μm; from a coastal Mediterranean lagoon) to a warming treatment (+3°C) and UVB radiation increases (+20%) at two different nutrient levels. Interestingly, the increase in temperature resulted in higher pigmented eukaryotes abundances and in community structure changes clearly illustrated by molecular analyses. For most of the phylogenetic groups, some rearrangements occurred at the OTUs level even when their relative proportion (microscope counting) did not change significantly. Temperature explained almost 20% of the total variance of the small eukaryote community structure (while UVB explained only 8.4%). However, complex cumulative effects were detected. Some antagonistic or non additive effects were detected between temperature and nutrients, especially for Dinophyceae and Cryptophyceae.
This multifactorial experiment highlights the potential impacts, over short time scales, of changing environmental factors on the structure of various functional groups like small primary producers, parasites and saprotrophs which, in response, can modify energy flow in the planktonic food webs.
PMCID: PMC3478981  PMID: 22966751
Small eukaryotes; Molecular diversity; Temperature; UVB radiation; Microcosms experiment; Mediterranean lagoon
2.  Application of a Specific and Sensitive Radiometric Assay for Microbial Lipase Activities in Marine Water Samples from the Lagoon of Nouméa 
Applied and Environmental Microbiology  2003;69(12):7395-7400.
Marine microbiologists commonly assay lipase activities by using a synthetic fluorescent analog, 4-methylumbelliferyl (MUF)-oleate. The technique is convenient, but it is considered to be unspecific because of the structure of this analog. This study reports the design of a new specific and sensitive lipase assay based on the use of a radiolabeled triglyceride, [3H]triolein. Free fatty acids (FFA) resulting from its hydrolysis are isolated as a function of time in a one-step liquid-liquid extraction and then radioassayed. MUF-oleate and [3H]triolein techniques were compared by measuring lipase activities at similar substrate concentrations along a trophic gradient in the Southwest Lagoon of New Caledonia, near Nouméa. Hydrolysis rates decreased from the nearshore station to the offshore station and showed similar trends regardless of the technique used. Rates decreased from 5.83 to 0.88 nmol of FFA · liter−1 · h−1 and from 0.76 to 0.23 nmol of 3H-FFA · liter−1 · h−1, respectively. These results appeared to be consistent with bacterial production results, which also decreased similarly (from 0.59 to 0.26 μg of C · liter−1 · h−1). However, the ratio of MUF-oleate activities to [3H]triolein activities, which was constant at the offshore stations (3.8 ± 0.1), gradually increased at the nearshore stations (from 4.1 to 7.6). This result shows that the two assays respond in different ways to changes in environmental conditions and validates the need to set up more specific enzymatic assays.
PMCID: PMC309873  PMID: 14660390

Results 1-2 (2)