Assessment of a low-frequency ultrasound device on prevention of biofilm formation and carbonate deposition in drinking water systems.

A device generating low-frequency and low-intensity ultrasound waves was used for mitigating biofilm accumulation and scaling. Two systems were tested: a lab-scale plate heat exchanger operated with continuously recycled water and a continually fed flow-through drinking water pilot used for mimicking water circulation in pipes. Initial deposition of bacterial cells was not prevented by ultrasound wave treatment.

Nano-exploration of organic conditioning film formed on polymeric surfaces exposed to drinking water.

Adsorption of organic macromolecules onto surfaces in contact with waters forms a so-called conditioning film and induces modifications of the surface properties. Here, we characterized conditioning films formed onto two hydrophobic materials (used as pipe liner) and immersed for 24 h in tap water. Using combination of atomic force microscopy (AFM), and chemical force microscopy (CFM), we detected some changes in roughness and hydrophilic/hydrophobic balance of the surface of the tested coupons, and also the deposition of numerous organic polymers (few millions/cm) randomly distributed on the surface.

Bacterial repopulation of drinking water pipe walls after chlorination.

The short-term kinetics of bacterial repopulation were evaluated after chlorination of high-density polyethylene (HDPE) colonized with drinking water biofilms and compared with bare HDPE surfaces. The effect of chlorination was partial as a residual biofilm persisted and was time-limited as repopulation occurred immediately after water resupply. The total number of bacteria reached the same levels on both the bare and chlorinated biofilm-fouled HDPE after a seven-day exposure to drinking water.

Patterned hydrophobic domains in the exopolymer matrix of Shewanella oneidensis MR-1 biofilms.

Water-dispersible amphiphilic surface-engineered quantum dots (QDs) were found to be strongly accumulated within discrete zones of the exopolymer network of Shewanella oneidensis MR-1 biofilms, but not on the cell surfaces. These microdomains showed a patterned distribution in the exopolymer matrix, which led to a restricted diffusion of the amphiphilic nanoparticles.

Cohesiveness and hydrodynamic properties of young drinking water biofilms.

Drinking water biofilms are complex microbial systems mainly composed of clusters of different size and age. Atomic force microscopy (AFM) measurements were performed on 4, 8 and 12 weeks old biofilms in order to quantify the mechanical detachment shear stress of the clusters, to estimate the biofilm entanglement rate ξ. This AFM approach showed that the removal of the clusters occurred generally for mechanical shear stress of about 100 kPa only for clusters volumes greater than 200 μm3.

Persistence and dissemination of the multiple-antibiotic-resistance plasmid pB10 in the microbial communities of wastewater sludge microcosms.

Plasmid-mediated dissemination of antibiotic resistance genes is widely recognized to take place in many environmental compartments but remains difficult to study in a global perspective because of the complexity of the environmental matrices considered and the lack of exhaustive tools. In this report, we used a molecular approach based on quantitative PCR to monitor the fate of the antibiotic resistance plasmid pB10 and its donor host in microbial communities collected from various wastewater treatment plant (WWTP) sludges and maintained in microcosms under different conditions. In aerated activated sludge microcosms, pB10 did not persist because of an apparent loss of the donor bacteria.

Improving the recovery of qPCR-grade DNA from sludge and sediment.

DNA extraction is often considered as the limiting step of most molecular approaches in ecology and environmental microbiology. Ten existing DNA extraction protocols were compared for recovery of DNA from sludge and a modified version of the protocol described by Porteous et al. (Mol Ecol 6:787-791, 1997) was determined to be the best method for recovery of DNA suitable for PCR.

Probing young drinking water biofilms with hard and soft particles.

The aim of our study was to investigate, through the use of soft (Escherichia coli) and hard (polystyrene microspheres) particles, the distribution and persistence of allochthonous particles inoculated in drinking water flow chambers. Biofilms were allowed to grow for 7-10 months in tap water from Nancy's drinking water network and were composed of bacterial aggregates and filamentous fungi. Both model particles adhered almost exclusively on the biofilms (i.

Adhesion of Campylobacter jejuni and Mycobacterium avium onto polyethylene terephtalate (PET) used for bottled waters.

Adhesion of the bacteria Campylobacter jejuni and Mycobacterium avium onto polyethylene terephtalate (PET), a polymer widely used within the bottled water industry was measured in two different groundwater solutions. From this, it was found that whilst the percentage cell adhesion for a given strain did not change between groundwater types, substantial variation was obtained between the two bacterial species tested: M. avium (10-30% adhered cells) and C.

Role of glutathione metabolism status in the definition of some cellular parameters and oxidative stress tolerance of Saccharomyces cerevisiae cells growing as biofilms.

The resistance of Saccharomyces cerevisiae to oxidative stress (H(2)O(2) and Cd(2+)) was compared in biofilms and planktonic cells, with the help of yeast mutants deleted of genes related to glutathione metabolism and oxidative stress. Biofilm-forming cells were found predominantly in the G1 stage of the cell cycle. This might explain their higher tolerance to oxidative stress and the young replicative age of these cells in an old culture.

Effect of wall shear rate on biofilm deposition and grazing in drinking water flow chambers.

The effect of four-wall shear rates (34.9, 74.8, 142.

Advantage provided by iron for Escherichia coli growth and cultivability in drinking water.

The presence of iron, used both as a nutrient and as an electron acceptor, was demonstrated to give an advantage to Escherichia coli bacteria in drinking water. Slight additions of ferrous sulfate to water with initial low iron concentrations led to a significant increase in the number of E. coli bacteria.

Nucleic acid fluorochromes and flow cytometry prove useful in assessing the effect of chlorination on drinking water bacteria.

Flow cytometry (FCM), combined with staining using two fluorochromes (propidium iodide, PI, or SYBR Green II RNA gel stain, SYBR-II), was used to assess nucleic acid injuries to chlorinated drinking water bacteria. Highly fluorescent SYBR-II-stained bacteria were converted to bacteria with low fluorescence after chlorination. PI staining of bacteria exposed to different doses of chlorine showed membrane permeabilisation ([Cl2] < 0.

Fatty acids of lipid fractions in extracellular polymeric substances of activated sludge flocs.

Phospholipid (PL), glycolipid (GL), and neutral lipid (NL) FA, and the lipopolysaccharide 2- and 3-hydroxy (LPS 2-OH and 3-OH) FA of activated sludges and extracted extracellular polymeric substances (EPS) were determined on samples collected from two wastewater treatment plants. EPS extracted from sludges by means of sonication and cation exchange contained proteins (43.4%), humic-like substances (11.

Influence of phosphate on bacterial adhesion onto iron oxyhydroxide in drinking water.

The transport and storage of drinking water in water distribution systems can modify its initial composition and properties. The accumulation of bacteria on corroded pipes is prejudicial and may lower the microbiological quality of the water. Previous results have shown that when pipes are highly corroded, the addition of phosphate, used as an anticorrosion treatment, decreases the bacterial concentration in the water.

Iron(II,III) hydroxycarbonate green rust formation and stabilization from lepidocrocite bioreduction.

Bioreduction of the well-crystallized ferric oxyhydroxide gamma-FeOOH lepidocrocite was investigated in batch cultures using Shewanella putrefaciens bacterium (strain CIP 8040) at initial pH 7.5 in bicarbonate buffer. The cultures were performed with formate as electron donor without phosphate, in the presence or absence of anthraquinone-2,6-disulfonate (AQDS) as electron shuttle.