Assessing the importance of a self-generated detachment process in river biofilm models

1. Epilithic biofilm biomass was measured for 14 months in two sites, located up‐ and downstream of the city of Toulouse in the Garonne River (south‐west France). Periodical sampling provided a biomass data set to compare with simulations from the model of Uehlinger, Bürher and Reichert (1996: Freshwater Biology, 36 , 249–263.), in order to evaluate the impact of hydraulic disturbance. 2. Despite differences in application conditions (e.g. river size, discharge, frequency of disturbance), the base equation satisfactorily predicted biomass between low and high water periods of the year, suggesting that the flood disturbance regime may be considered a universal mechanism controlling periphyton biomass. 3. However modelling gave no agreement with biomass dynamics during the 7‐month long low water period that the river experienced. The influence of other biomass‐regulating factors (temperature, light and soluble reactive phosphorus) on temporal biomass dynamics was weak. 4. Implementing a supplementary mechanism corresponding to a temperature‐dependent self‐generated loss because of heterotrophic processes allowed us to accurately reproduce the observed pattern: a succession of two peaks. This case study suggests that during typical summer low water periods (flow stability and favourable temperature) river biofilm modelling requires self‐generated detachment to be considered.     

Biofilm reactors in anaerobic wastewater treatment

Attached biofilm reactors provide the means for implementing energy-efficient anaerobic wastewater treatment at full scale. Progress has been made in the development of fixed, expanded and fluidized bed anaerobic processes by addressing fundamental reactor design issues. Several new biofilm reactor concepts have evolved from recent studies.     

Methyl mercury uptake by free and immobilized cyanobacterium

Methyl mercury uptake in free cells and different immobilizates of the cyanobacteriumNostoc calcicola has been examined. The general growth of the immobilized cyanobacterial cells could be negatively correlated with methyl mercury uptake. Alginate spheres proved most efficient in terms of uptake rate (0.48 nmol mg protein^–1 min^–1, 10 min) and total bioaccumulation (10.71 nmol mg protein^–1, 1 h) with a bioconcentration factor of 3.3×10³. Alginate biofilms showed a faster methyl mercury accumulation rate (0.83 nmol mg protein^–1 min^–1, 10 min) with a saturation of 10.28 nmol mg protein^–1 reached within only 30 min (bioconcentration factor, 3.1×10³). Foam preparations with a slow initial uptake approximated biofilms but were characterized by a lower bioconcentration factor (2.8×10³). Free cells, in comparison, maintained the initial slow rate of uptake (0.62 nmol mg protein^–1 min^–1, 10 min), saturating at 30 min (8.81 nmol mg protein^–1), and the resultant lowest bioconcentration factor (2.7×10³). Cell ageing (30 days) brought a drastic reduction (3-fold) in organomercury uptake by free cells while alginate spheres maintained the same potential. Foam preparations of the same age showed a significant improvement in methyl mercury uptake followed by only a marginal decline in alginate biofilms. Data are discussed in the light of the physiological efficiency and longevity of immobilized cells.     

Cyanobacteria of Rocks and Soils of the Orinoco Lowlands and the Guayana Uplands,Venezuela

The occurrence of 23 cyanobacterial species, belonging to 9 different genera and 5 cyanobacterial lichen species of 5 different genera on exposed, open rock surfaces of inselbergs and on soil in savannas of the Orinoco lowlands and the Guayana uplands is described. Their distribution patterns and frequency within the different habitats are given. The filamentous procaryotic blue-green algae/cyanobacteria Stigonema ocellatum and Scytonema crassum, together with the unicellular cyanobacterium Gloeocapsa sanguinea were the most frequent species on rocks, whereas the filamentous cyanobacterium, Schizothrix telephoroides, dominated in cyanobacterial mats on the savanna soil. All species showed intensively coloured sheaths, either brown or yellow in the case of Stigonema ocellatum and Scytonema crassum, or red in Gloeocapsa sanguinea and Schizothrix telephoroides. In addition, a number of cyanobacterial lichens occurred.     

A dual fluorescence technique for visualization ofStaphylococcus epidermidis biofilm using scanning confocal laser microscopy

A new dual fluorescence technique is described which, when combined with scanning confocal laser microscopy (SCLM), can be used to visualize the components of biofilm produced byStaphylococcus epidermidis. Chemostat cultures of RP62A (a well-characterized slime-producing strain ofS. epidermidis) were used to produce mature biofilm on polyvinylcholoride (PVC) disks immobilized in a modified Robbins device using a seed and feed model system. Serial horizontal and vertical optical thin sections, as well as three-dimensional computer reconstructions, were obtained onin situ biofilm using the dual fluorescence procedure. Bacteria were visualized by green autofluorescence excited at 488 nm with an Argon laser. Cell-associated and exocellular matrix material (slime) was visualized by red fluorescence excited at 568 nm with a Krypton laser after interaction of the biofilm with Texas Red-labeled wheat germ agglutinin which is a slime-specific lectin marker. Structural analysis revealed that the cocci grew in slime-embedded cell clusters forming distinct conical-shaped microcolonies. Interspersed open channels served to connect the bulk liquid with the deepest layers of the mature, hydrated biofilm which increased overall surface area and likely facilitated the exchange of nutrients and waste products throughout the biofilm. The combined dual fluorescence technique and SCLM is potentially useful as a specific noninvasive tool for studying the effect of antimicrobial agents on the process of biofilm formation and for the characterization of the architecture ofS. epidermidis biofilm formedin vivo andin vitro on medical grade virgin or modified inert polymer surfaces.     

Quantitative analysis of biofilm thickness variability

The thickness variability of biofilms of Pseudomonas aeruginosa, Klebsiella pneumoniae, and the binary population combination of these two species was quantified. The experimental method involved cryoembedding biofilms with a commercial tissue embedding agent, sectioning, and applying image analysis to construct thickness profiles along linear transects (up to 1 cm in length) across the substratum. Biofilms embedded and sectioned by this method were locally as thin as a single cell attached to the surface (<5 mum) and as thick as 1000 mum. Week-old biofilms of three different species compositions displayed distinct structural features as indicated by their mean thicknesses and by a roughness coefficient. Monopopulation biofilms of P. aeruginosa (29 mum mean thickness) or K. pneumoniae (100 mum mean thickness) were thinner than the binary population biofilm (400 mum mean thickness). A roughness coefficient developed in this investigation corroborated the qualitative visual characterization of P. aeruginosa biofilms as relatively uniformly thick (mean roughness coefficient 0.15), K. pneumoniae biofilms as patchy (mean roughness coefficient 1.14), and the binary population biofilm as intermediate (mean roughness coefficient 0.26). Whereas P. aeruginosa and binary population biofilms covered the substratum completely, significant areas of essentially bare substratum were apparent in K. pneumoniae biofilms. The patchiness of K. pneumoniae biofilms may be due to the fact that this organism is nonmotile. A spatial correlation analysis of the thickness data indicated that thickness measurements were still correlated even when separated by distances that exceeded the mean biofilm thickness. Cell aggregates, some of them hundreds of microns in size, were observed in the effluent of K. pneumoniae and binary population biofilm reactors. Measurements of thickness variability and other observations reported in this article provide a quantitative basis for analysis of microscale structural heterogeneity of biofilms. (c) 1995 John Wiley & Sons, Inc.     

A modeling study of anaerobic biofilm systems: II. Reactor modeling

A rigorous steady-state model of anaerobic biofilm reactors taking into account acid-base and gas-phase equilibria in the reactor in conjunction with detailed chemical equilibria and mass transfer in acetate-utilizing methanogenic biofilms is presented. The performances of ideal completely stirred tank reactors (CSTRs) and plug-flow reactors, as well as reactors with nonideal hydraulic conditions, are simulated. Decreasing the surface loading rate increases the acetate removal efficiency, while decreasing the influent pH and increasing the buffering capacity improves the removal efficiency only if the bulk pH of the reactor shifts toward more optimal values between 6.8 to 7.0. The reactor can have negative or positive removal efficiencies depending on the start-up conditions. The respiration coefficient plays a critical role in determining the minimum influent pH required for reactor recovery after failure. Having multiple CSTRs-in-series generally increases the overall removal efficiency for the influent conditions investigated. Monitoring of the influent feed quality is critical for plug-flow reactors, becasue failure of the initial sections of the reactor may cause a cascading effect that may lead to a rapid reactor failure. (c) 1995 John Wiley & Sons, Inc.     

Formation of nesquehonite and other minerals as a consequence of biofilm dehydration

A microbial biofilm community was established over 971 days within gravel in an aquarium so as to model biofouling of an aquifer. When the water was allowed to evaporate slowly, white crystalline deposits, containing several carbonate and sulphate minerals including nesquehonite (MgCO₃.3H2O), were seen at the highest points on the surface of the biofouled gravel. No such deposits occurred in regions lacking biofilms. These crystals appeared to originate from evaporation of dissolved salts which had migrated through the biofilm. Surfaceadherent microbial biofilms may conceivably provide a conduit for solute transport in porous media such as soils and aquifers.