Jean-Luc Rols

A photosynthetic rotating annular bioreactor (Taylor–Couette type flow) for phototrophic biofilm cultures

In their natural environment, the structure and functioning of microbial communities from river phototrophic biofilms are driven by biotic and abiotic factors. An understanding of the mechanisms that mediate the community structure, its dynamics and the biological succession processes during phototrophic biofilm development can be gained using laboratory-scale systems operating with controlled parameters. For this purpose, we present the design and description of a new prototype of a rotating annular bioreactor (RAB) (Taylor-Couette type flow, liquid working volume of 5.04 L) specifically adapted for the cultivation and investigation of phototrophic biofilms. The innovation lies in the presence of a modular source of light inside of the system, with the biofilm colonization and development taking place on the stationary outer cylinder (onto 32 removable polyethylene plates). The biofilm cultures were investigated under controlled turbulent flowing conditions and nutrients were provided using a synthetic medium (tap water supplemented with nitrate, phosphate and silica) to favour the biofilm growth. The hydrodynamic features of the water flow were characterized using a tracer method, showing behaviour corresponding to a completely mixed reactor. Shear stress forces on the surface of plates were also quantified by computer simulations and correlated with the rotational speed of the inner cylinder. Two phototrophic biofilm development experiments were performed for periods of 6.7 and 7 weeks with different inoculation procedures and illumination intensities. For both experiments, biofilm biomasses exhibited linear growth kinetics and produced 4.2 and 2.4 mg cm(-)² of ash-free dry matter. Algal and bacterial community structures were assessed by microscopy and T-RFLP, respectively, and the two experiments were different but revealed similar temporal dynamics. Our study confirmed the performance and multipurpose nature of such an innovative photosynthetic bioreactor for phototrophic biofilm investigations.

Procedures in Ready Biodegradability Testing: Effects of the Inoculation and the Monitored Parameter

Ready biodegradability tests are often limited because of a lack of definition in some operating conditions, which can be critical for reproducibility and efficiency. In this paper, the effects of the monitored analytical parameter and the variations in the inoculum quantity on test results are studied. In a Sturm standardized assay, sodium acetate and dodecylbenzene sulfonate (DBS) were tested at several initial substrate to biomass ratios (S0/X0). The analytical parameter did show itself to be determinant in the estimation of the extent of the acetate biodegradation. In DBS assays, imposed S0/X0 ratios did control both lag time and biodegradation level as well as final carbon distribution in cellular, mineralized and residual carbon. Therefore, quantitative measurement of the S0/X0 ratio, or alternatively its setting at a certain value, could enhance the reliability of test results. In order to improve the comparison between different analytical procedures, a low S0/X0 ratio is deemed advantageous. The ...

Changes in tolerance to herbicide toxicity throughout development stages of phototrophic biofilms

Ecotoxicological experiments have been performed in laboratory-scale microcosms to investigate the sensitivity of phototrophic biofilm communities to the alachlor herbicide, in relation to the stages of phototrophic biofilm maturation (age of the phototrophic biofilms) and physical structure (intact biofilm versus recolonization). The phototrophic biofilms were initially cultivated on artificial supports in a prototype rotating annular bioreactor (RAB) with Taylor-Couette type flow under constant operating conditions. Biofilms were collected after 1.6 and 4.4 weeks of culture providing biofilms with different maturation levels, and then exposed to nominal initial alachlor concentration of 10 μg L(-1) in either intact or recolonized biofilms for 15 days in microcosms (mean time-weighted average concentration - TWAC of 5.52 ± 0.74 μg L(-1)). At the end of the exposure period, alachlor effects were monitored by a combination of biomass descriptors (ash-free dry mass - AFDM, chlorophyll a), structural molecular fingerprinting (T-RFLP), carbon utilization spectra (Biolog) and diatom species composition. We found significant effects that in terms of AFDM, alachlor inhibited growth of the intact phototrophic biofilms. No effect of alachlor was observed on diatom composition or functional and structural properties of the bacterial community regardless of whether they were intact or recolonized. The intact three-dimensional structure of the biofilm did not appear to confer protection from the effects of alachlor. Bacterial community structure and biomass level of 4.4 weeks - intact phototrophic biofilms were significantly influenced by the biofilm maturation processes rather than alachlor exposure. The diatom communities which were largely composed of mobile and colonizer life-form populations were not affected by alachlor. This study showed that the effect of alachlor (at initial concentration of 10 μg L(-1) or mean TWAC of 5.52 ± 0.74 μg L(-1)) is mainly limited to biomass reduction without apparent changes in the ecological succession trajectories of bacterial and diatom communities and suggested that carbon utilization spectra of the biofilm are not damaged resulting. These results confirmed the importance of considering the influence of maturation processes or community age when investigating herbicide effects. This is particularly important with regard to the use of phototrophic biofilms as bio-indicators.

Standardization of activated sludge for biodegradation tests

AbstractActivated sludges are an inoculum source commonly used in biodegradation studies, as wastewater treatment facilities constitute an entry point to the environment for many chemicals. In this paper, the main issues relating to the use of activated sludge in biodegradability tests are presented. Special attention is also devoted to discussing the factors affecting both the activity of the microbial communities and the test results. After a short survey of the state of the art of microbiology of activated sludge, the paper focuses on the methods used to reduce the variations in the diversity, quality and quantity of these communities. Finally, use of surrogates as reference materials in biodegradability tests is discussed. FigureGraphical abstract

Activated sludge as inoculum for ready biodegradability testing: effect of source.

Abstract Results of ready biodegradability tests (RBT) are barely reproducible owing to a well‐known lack of definition in inoculum source and quality. In this study, the degree of variability expected when only activated sludges are used as inoculum source was investigated. For this, the characteristics of activated sludges collected in municipal wastewater treatment plants operating at various massic loading rates (MLR; 0.1, 0.5 and 0.9 kgBOD, kgVSS‐1 d‐1) were compared. In order to provide suitable cellular densities for RBT, inocula were obtained after settling of activated sludges and analyzed in terms of active and cultivable cell densities, dehydrogenasic activity, BODS and a general profile of hydrolytic enzymes. In our analysis, biomass obtained from the High‐MLR treatment plant constituted the inoculum having the highest biodegradation potential both with respect to microbial densities and to enzyme activities. This biomass also yielded the fastest biodégradation kinetics in dodecyl benzene sulfonate RBT. An attempt of biomass homogenization of inocula on the basis of cultivable cell density and dehydrogenasic activity gave negative results with this chemical compound. Since, in practice, restriction of activated sludge sources may be difficult, our results emphasize the importance of further studies aimed at homogenization of inoculum quality and quantity.

Metal contaminations impact archaeal community composition, abundance and function in remote alpine lakes: Metal contaminations impact archaeal diversity facets

Using the 16S rRNA and mcrA genes, we investigated the composition, abundance and activity of sediment archaeal communities within 18 high-mountain lakes under contrasted metal levels from different origins (bedrock erosion, past-mining activities and atmospheric depositions). Bathyarchaeota, Euryarchaeota and Woesearchaeota were the major phyla found at the meta-community scale, representing 48%, 18.3% and 15.2% of the archaeal community respectively. Metals were equally important as physicochemical variables in explaining the assemblage of archaeal communities and their abundance. Methanogenesis appeared as a process of central importance in the carbon cycle within sediments of alpine lakes as indicated by the absolute abundance of methanogen 16S rRNA and mcrA gene transcripts (105 to 109 copies g-1 ). We showed that methanogen abundance and activity were significantly reduced with increasing concentrations of Pb and Cd, two indicators of airborne metal contaminations. Considering the ecological importance of methanogenesis in sediment habitats, these metal contaminations may have system wide implications even in remote area such as alpine lakes. Overall, this work was pioneer in integrating the effect of long-range atmospheric depositions on archaeal communities and indicated that metal contamination might significantly compromise the contribution of Archaea to the carbon cycling of the mountain lake sediments.

Corrigendum to “Zn isotope fractionation during interaction with phototrophic biofilm” [Chemical Geology 390 (2014) 46–60]

a Universite de Toulouse, UPS, GET (Geosciences and Environment Toulouse) UMR 5563 CNRS, 14 Avenue Edouard Belin, 31400 Toulouse, France b CNRS, GET, 31400 Toulouse, France c Universite de Toulouse, INP, UPS, EcoLab (Laboratoire Ecologie Fonctionnelle et Environnement), 118 Route de Narbonne, 31062 Toulouse, France d CNRS, EcoLab, 31062 Toulouse, France e BIO-GEO-CLIM Laboratory, Tomsk State University, Tomsk, Russia