How can one measure group cohesion? From individual organisms to their interaction

Measuring atomic and molecular interactions was one of the main objectives of physics during the past century. It was an essential step not only in itself but because most macroscopic properties can be derived once one knows interaction strengths. At the present time, except for systems that can be described as discrete networks (like the Internet network) our knowledge of social and biological ties still remains very limited. An important step is to develop experimental means for measuring social and biological interactions. In this talk there are two parts. Firstly, we describe experimental evidence of inter-individual attraction in populations of insects. Secondly, we focus on a specific system, namely populations of Euglena gracilis, a green, swimming unicellular organism, for which we try to determine individual and interaction properties

On the use of the FluoroProbe®, a phytoplankton quantification method based on fluorescence excitation spectra for large-scale surveys of lakes and reservoirs

Although microscope analysis is very useful for studying phytoplankton communitycomposition, it does not allow for high frequency (spatial and/or temporal) data acquisi-tion. In an attempt to overcome this issue, fluorescence-based approaches that useselective excitation of pigment antennae have spread rapidly. However, the ability of spectral fluorescence to provide accurate estimates of phytoplankton biomass andcomposition is still debated, and only a few datasets have been tested to date.In this study, we sampled of a wide range of water bodies (n¼50) in the Ile-de-Franceregion (North Central France). We used the resulting extensive dataset to assess theability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton communitycomposition in lakes and reservoirs.We demonstrated that FP data yields better estimates of total phytoplankton biovolumethan do spectrophotometric chlorophyllameasures and that FP data can be further cor-rected using the average chlorophyllato biovolume ratio among phytoplankton groups.Overall, group-specific relationships between FP and biovolume data were consistent.However, we identified a number of cases where caution is required. We found thatEuglenophytes are expected to depart from the global FPvs.biovolume relationship of the‘green’ group due to varying Fv/Fm and pigment content in response to environmentalconditions (photoautotrophicvs.photoheterotrophic growth). Then, it appears necessaryto consider the composition of the Chromophytes community in order to obtain a goodagreement between both biomass estimation methods. Finally, we confirmed the misat-tribution toward the ‘red’ group of phycoerythrin-containing cyanobacteria and theoccurrence of a strong scattering in the relationship between the FPvs.biovolume of the‘blue’ group that can be partly attributed to the occurrence of large colony-forming cya-nobacteria (e.g.,Microcystisspp,Aphanizomenon flos-aquae).We propose correcting procedures to improve the quality of data obtained from spectral fluorescence tools in the context of large-scale sampling of lakes and reservoirs

Nano-gold biosynthesis by silica-encapsulated micro-algae : a "living" bio-hybrid material

International audienc

Effects of water absorption and surface roughness on the bioreceptivity of ETICS compared to clay bricks

External thermal insulation composite systems (ETICS) have been used in European buildings since the 70’s due to the optimal protection from thermal loss, the low cost and the ease of application. The progressive thickening of ETICS used for either thermal insulation in new buildings or energy requalification of ancient buildings has facilitated the growth of microalgae on façades, due to limitation of outgoing heat flux, and hence to condensation of atmospheric moisture on building façade external layer. This study was aimed to comparatively evaluating the growth of two selected microalgal strains on ETICS and fired clay bricks; to this end, the influence of water absorption, porosity and surface roughness of these building materials was investigated. Biodeterioration of building materials was induced through a laboratory-accelerated growth test. Results from colorimetric and confocal laser scanning microscopy (CLSM) analyses clearly demonstrated that bioreceptivity of the building materials assayed is strongly affected by surface roughness and total porosit