Juan P. Pavissich

Culture dependent and independent analyses of bacterial communities involved in copper plumbing corrosion.

Aims:u2002 This study used culture‐dependent and culture‐independent approaches to characterize bacterial communities in copper plumbing corrosion and to assess biofilm formation and copper resistance of heterotrophic bacteria isolated from copper pipes.

Multicomponent model of deformation and detachment of a biofilm under fluid flow

A novel biofilm model is described which systemically couples bacteria, extracellular polymeric substances (EPS) and solvent phases in biofilm. This enables the study of contributions of rheology of individual phases to deformation of biofilm in response to fluid flow as well as interactions between different phases. The model, which is based on first and second laws of thermodynamics, is derived using an energetic variational approach and phase-field method. Phase-field coupling is used to model structural changes of a biofilm. A newly developed unconditionally energy-stable numerical splitting scheme is implemented for computing the numerical solution of the model efficiently. Model simulations predict biofilm cohesive failure for the flow velocity between and m s−1 which is consistent with experiments. Simulations predict biofilm deformation resulting in the formation of streamers for EPS exhibiting a viscous-dominated mechanical response and the viscosity of EPS being less than . Higher EPS viscosity provides biofilm with greater resistance to deformation and to removal by the flow. Moreover, simulations show that higher EPS elasticity yields the formation of streamers with complex geometries that are more prone to detachment. These model predictions are shown to be in qualitative agreement with experimental observations.

Novel polymerase chain reaction primers for the specific detection of bacterial copper P-type ATPases gene sequences in environmental isolates and metagenomic DNA.

Aims:u2002 In the last decades, the worldwide increase in copper wastes release by industrial activities like mining has driven environmental metal contents to toxic levels. For this reason, the study of the biological copper‐resistance mechanisms in natural environments is important. Therefore, an appropriate molecular tool for the detection and tracking of copper‐resistance genes was developed.

Sulfate reduction, molecular diversity, and copper amendment effects in bacterial communities enriched from sediments exposed to copper mining residues.

Sulfate-reducing bacterial communities from coastal sediments with a long-term exposure to copper (Cu)-mining residues were studied in lactate enrichments. The toxicity of excess copper may affect sulfate-reducing bacterial communities. Sulfate reduction was monitored by sulfate and organic acid measurements. Molecular diversity was analyzed by 16S rRNA, dissimilatory sulfate reduction dsrAB, and Cu translocating phospho-type adenosine triphosphatases (P-ATPases) cop-like gene sequence profiling. The influence of Cu amendment was tested in these enrichments. Results showed fast sulfate reduction mostly coupled to incomplete organic carbon oxidation and partial sulfate reduction inhibition due to copper amendment. The 16S rRNA clonal libraries analysis indicated that delta- and gamma-Proteobacteria and Cytophaga-Flexibacter-Bacteroides dominated the enrichments. The dsrAB libraries revealed the presence of Desulfobacteraceae and Desulfovibrionaceae families-related sequences. Copper produced significant shifts (i.e., a decrease in the relative abundance of sulfate-reducing microorganisms) in the enriched bacterial community structure as determined by terminal-restriction fragment length polymorphism (T-RFLP) profiling and multivariate analyses. Clonal libraries of cop-like sequences showed low richness in the enriched microbial communities, and a strong effect of copper on its relative abundance. Novel Cu-P(IB)-ATPase sequences encoding Cu resistance were detected. The present study indicates that Cu does not significantly affect sulfate reduction and genetic diversity of taxonomic and dissimilatory sulfate-reduction molecular markers. However, the diversity of Cu resistance genetic determinants was strongly modified by this toxic metal.

A methodology to assess the effects of biofilm roughness on substrate fluxes using image analysis, substrate profiling, and mathematical modelling.

We present a novel approach, based on image analysis and modelling, to study the impact of morphological variability (roughness) and fluid dynamics on substrate mass fluxes in biofilms. Specifically, we used this method to assess substrate fluxes in counter-diffusional autotrophic biofilms in a hydrogen-based membrane biofilm reactor. The physical structure of the biofilm was determined in situ at the meso-scale using stereomicroscopy. Image analysis was used to characterize the biofilm structure, and substrate profiles were obtained using microsensors. A two-dimensional, continuum biofilm model including microbial reactions, mass transport, and fluid dynamics was developed to compute substrate conversion in irregularly shaped counter-diffusional biofilms. Experimental biofilm structures were reproduced in the model and simulated under the prevailing substrate and hydrodynamic conditions for flow velocities varied over three orders of magnitude. Model calculations were consistent with experimental results and showed enhanced conversion rates with increased roughness at higher flow velocities. Also, modelling showed that conversion rates in counter-diffusional biofilms were typically higher than in co-diffusional biofilms. This study highlights the potential to use a simple image acquisition approach coupled to a theoretical model, to evaluate biofilm overall substrate utilization related to biofilm morphological heterogeneity.

Multi-technique approach to assess the effects of microbial biofilms involved in copper plumbing corrosion

Microbially influenced corrosion (MIC) is recognized as an unusual and severe type of corrosion that causes costly failures around the world. A microbial biofilm could enhance the copper release from copper plumbing into the water by forming a reactive interface. The biofilm increases the corrosion rate, the mobility of labile copper from its matrix and the detachment of particles enriched with copper under variable shear stress due to flow conditions. MIC is currently considered as a series of interdependent processes occurring at the metal-liquid interface. The presence of a biofilm results in the following effects: (a) the formation of localized microenvironments with distinct pH, dissolved oxygen concentrations, and redox conditions; (b) sorption and desorption of labile copper bonded to organic compounds under changing water chemistry conditions; (c) change in morphology by deposition of solid corrosion by-products; (d) diffusive transport of reactive chemical species from or towards the metal surface; and (e) detachment of scale particles under flow conditions. Using a multi-technique approach that combines pipe and coupon experiments this paper reviews the effects of microbial biofilms on the corrosion of copper plumbing systems, and proposes an integrated conceptual model for this phenomenon supported by new experimental data.

Impact of copper on the abundance and diversity of sulfate-reducing prokaryotes in two chilean marine sediments

We studied the abundance and diversity of the sulfate-reducing prokaryotes (SRPs) in two 30-cm marine chilean sediment cores, one with a long-term exposure to copper-mining residues, the other being a non-exposed reference sediment. The abundance of SRPs was quantified by qPCR of the dissimilatory sulfite reductase gene β-subunit (dsrB) and showed that SRPs are sensitive to high copper concentrations, as the mean number of SRPs all along the contaminated sediment was two orders of magnitude lower than in the reference sediment. SRP diversity was analyzed by using the dsrB-sequences-based PCR-DGGE method and constructing gene libraries for dsrB-sequences. Surprisingly, the diversity was comparable in both sediments, with dsrB sequences belonging to Desulfobacteraceae, Syntrophobacteraceae, and Desulfobulbaceae, SRP families previously described in marine sediments, and to a deep branching dsrAB lineage. The hypothesis of the presence of horizontal transfer of copper resistance genes in the microbial population of the polluted sediment is discussed.

Kinetics of nitrous oxide (N2O) formation and reduction by Paracoccus pantotrophus

Nitrous oxide (N2O) is a powerful greenhouse gas emitted from wastewater treatment, as well as natural systems, as a result of biological nitrification and denitrification. While denitrifying bacteria can be a significant source of N2O, they can also reduce N2O to N2. More information on the kinetics of N2O formation and reduction by denitrifying bacteria is needed to predict and quantify their impact on N2O emissions. In this study, kinetic parameters were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Parameters included the maximum specific reduction rates,

Copper Corrosion and Biocorrosion Events in Premise Plumbing

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