Enhanced Biocide Treatments with D-amino Acid Mixtures against a Biofilm Consortium from a Water Cooling Tower

Different species of microbes form mixed-culture biofilms in cooling water systems. They cause microbiologically influenced corrosion (MIC) and biofouling, leading to increased operational and maintenance costs. In this work, two D-amino acid mixtures were found to enhance two non-oxidizing biocides [tetrakis hydroxymethyl phosphonium sulfate (THPS) and NALCO 7330 (isothiazoline derivatives)] and one oxidizing biocide [bleach (NaClO)] against a biofilm consortium from a water cooling tower in lab tests. Fifty ppm (w/w) of an equimass mixture of D-methionine, D-leucine, D-tyrosine, D-tryptophan, D-serine, D-threonine, D-phenylalanine, and D-valine (D8) enhanced 15 ppm THPS and 15 ppm NALCO 7330 with similar efficacies achieved by the 30 ppm THPS alone treatment and the 30 ppm NALCO 7330 alone treatment, respectively in the single-batch 3-h biofilm removal test. A sequential treatment method was used to enhance bleach because D-amino acids react with bleach. After a 4-h biofilm removal test, the sequential treatment of 5 ppm bleach followed by 50 ppm D8 achieved extra 1-log reduction in sessile cell counts of acid producing bacteria, sulfate reducing bacteria, and general heterotrophic bacteria compared with the 5 ppm bleach alone treatment. The 10 ppm bleach alone treatment showed a similar efficacy with the sequential treatment of 5 ppm bleach followed by 50 ppm D8. The efficacy of D8 was found better than that of D4 (an equimass mixture of D-methionine, D-leucine, D-tyrosine, and D-tryptophan) in the enhancement of the three individual biocides against the biofilm consortium

CRL4 antagonizes SCFFbxo7-mediated turnover of cereblon and BK channel to regulate learning and memory

Intellectual disability (ID), one of the most common human developmental disorders, can be caused by genetic mutations in Cullin 4B (Cul4B) and cereblon (CRBN). CRBN is a substrate receptor for the Cul4A/B-DDB1 ubiquitin ligase (CRL4) and can target voltage- and calcium-activated BK channel for ER retention. Here we report that ID-associated CRL4CRBNmutations abolish the interaction of the BK channel with CRL4, and redirect the BK channel to the SCFFbxo7ubiquitin ligase for proteasomal degradation. Glioma cell lines harbouring CRBN mutations record density-dependent decrease of BK currents, which can be restored by blocking Cullin ubiquitin ligase activity. Importantly, mice with neuron-specific deletion of DDB1 or CRBN express reduced BK protein levels in the brain, and exhibit similar impairment in learning and memory, a deficit that can be partially rescued by activating the BK channel. Our results reveal a competitive targeting of the BK channel by two ubiquitin ligases to achieve exquisite control of its stability, and support changes in neuronal excitability as a common pathogenic mechanism underlying CRL4CRBN–associated ID

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Inclusion chromatography using cyclodextrin-containing resins and studies of nonlinear chromatographic theories

Cylcodextrins are a family of cyclic-oligosaccharides, containing usually six to eight glucopyranose units. Because of their unique donut-shaped steric structure they are able to form inclusion complexes selectively with some guest molecules. In this work, a novel method of synthesizing cyclodextrin-containing resins for inclusion chromatography has been developed. Resins synthesized with this method possess a very high content of cyclodextrins and good physical properties. Experiments on the adsorption isotherms and stepwise adsorption/desorption column operations have been carried out to separate some biomolecules. Efforts have been made to recover phenylalanine from industrial waste samples using a $\beta$-Cyclodextrin column. Some water soluble aliphatic alcohols have been found to be good displacers. A robust and efficient numerical procedure has been developed to solve a general multicomponent rate model which considers axial dispersion, external film mass transfer, intraparticle diffusion and nonlinear isotherms. The method uses finite element and orthogonal collocation methods to discretize the bulk phase and particle phase partial differential governing equations, respectively. The resulting ordinary differential equation system is then solved by Gear\u27s stiff method. The model has also been extended to include second order kinetics, size exclusion, and the reaction between soluble ligands and macromolecules in the fluid phase for the study of affinity chromatography. Computer simulations of stepwise displacement qualitatively proved some of the experimental observations. A methodology has been developed to derive kinetic and isotherm models, which have successfully demonstrated isotherm cross-over and peak reversal phenomena for multicomponent systems with uneven saturation capacities. A unified approach based on a displacement effect has been proposed to explain the dominating interference effect in multicomponent chromatography. System peak patterns in binary elution have been summarized. Various aspects, including operational stages, the rate-limiting step and two types of inhibition in affinity chromatography have been analyzed. Multicomponent rate models for radial flow chromatography (RFC) have also been solved using an accurate numerical treatment in which the radial dispersion and the external film mass transfer coefficients are treated as variables. A comparison of, and mathematical analogy between, RFC and conventional axial flow chromatography have been made

Biocorrosion caused by microbial biofilms is ubiquitous around us

Biocorrosion first surfaced in the scientific literature when Richard H. Gaines associated corrosion with bacterial activities in 1910. It is also known as microbiologically influenced corrosion (MIC). In general, it covers two scenarios. One is that microbes cause corrosion directly, which usually means microbes secrete corrosive metabolites or microbes harvest electrons from a metal for respiration to produce energy. In the second scenario, microbes are behind the initiation or acceleration of corrosion caused by a pre-existing corrosive agent such as water and CO2, by compromising the passive film (often a metal oxide film on a metal). MIC is caused by microbial biofilms. It is everywhere around us. This work dissects some notable examples with perspectives

Anaerobic Corrosion of 304 Stainless Steel Caused by the Pseudomonas aeruginosa Biofilm

Pseudomonas aeruginosa is a ubiquitous bacterium capable of forming problematic biofilms in many environments. They cause biocorrosion of medical implants and industrial equipment and infrastructure. Aerobic corrosion of P. aeruginosa against stainless steels has been reported by some researchers while there is a lack of reports on anaerobic P. aeruginosa corrosion in the literature. In this work, the corrosion by a wild-type P. aeruginosa (strain PAO1) biofilm against 304 stainless steel (304 SS) was investigated under strictly anaerobic condition for up to 14 days. The anaerobic corrosion of 304 SS by P. aeruginosa was reported for the first time. Results showed that the average sessile cell counts on 304 SS coupons after 7- and 14-day incubations were 4.8 × 107 and 6.2 × 107 cells/cm2, respectively. Scanning electron microscopy and confocal laser scanning microscopy corroborated the sessile cell counts. The X-ray diffraction analysis identified the corrosion product as iron nitride, confirming that the corrosion was caused by the nitrate reducing biofilm. The largest pit depths on 304 SS surfaces after the 7- and 14-day incubations with P. aeruginosa were 3.9 and 7.4 μm, respectively. Electrochemical tests corroborated the pitting data

Preliminary Proof-of-Concept Testing of Novel Antimicrobial Heat-Conducting “Metallic” Coatings Against Biofouling and Biocorrosion

NiMo (nickel-molybdenum) and NiMo with embedded CeO2 nanoparticles (NPs; 100 nm) were tested as antimicrobial coatings (~15 μm thickness) on titanium (Ti) surfaces using an electrochemical process for heat exchanger applications onboard marine vessels. Preliminary static biofouling and biocorrosion (also known as microbiologically influenced corrosion) assessments were carried out in glass bottles using pure-culture Desulfovibrio vulgaris, a sulfate-reducing bacterium (SRB), in deoxygenated ATCC 1249 medium at 37°C, and using an alga (Chlorella vulgaris) mixed with general heterotrophic bacteria (GHB) in enriched artificial seawater at 28°C. It was found that the coating containing NiMo/CeO2 NPs were much more effective than NiMo in preventing SRB biofilm formation with an efficacy of 99% reduction in D. vulgaris sessile cells after 21 day incubation. The coating also exhibited a 50% lower corrosion current density compared to the uncoated Ti against SRB corrosion. Both NiMo and NiMo/CeO2 NP coatings achieved 99% reduction in sessile algal cells. Confocal laser scanning microscopy (CLSM) biofilm images indicated a large reduction of sessile GHB cells. The CLSM images also confirmed the biocidal kill effects of the two coatings. Unlike polymer coatings, the “metallic” coatings are heat conductive. Thus, the corrosion resistant antifouling coatings are suitable for heat exchanger applications

A Practical Mechanistic Model for MIC Based on a Biocatalytic Cathodic Sulfate Reduction Theory,” CORROSION/2009, Paper No. 09390

ABSTRACT Microbiologically induced corrosion (MIC) due to sulfate-reducing bacteria (SRB) is a major problem facing the oil and gas industry as well as other industries such as water utility. Current risk-factor probability models are useful in predicting the likelihood of MIC. However the reliable prediction of the progression of MIC pitting must depend on mechanistic modeling. This paper presents a mechanistic model for the prediction of MIC pitting progression based on a biocatalytic cathodic sulfate reduction (BCSR) theory. The hydrogenase system in the sessile SRB cells at the interface of biofilm and metal surface is treated as a bio-electrocatalyst for sulfate reduction. The model considers both charge transfer resistance and mass transfer resistance. It can be calibrated using an experimentally measured electrochemical parameter recast as "biofilm aggressiveness" for a particular SRB biofilm. Other charge transfer and mass transfer parameters are used as available in the literature or from existing experimental correlations. Computer simulation indicates that charge transfer resistance is important initially when the biofilm thickness is small. However, mass transfer resistance becomes dominant after pit grows to a sizable depth. In fact, the growth of any deep pits will always be mass transfer controlled regardless of how aggressive the biofilm is

Toward a better understanding of microbiologically influenced corrosion caused by sulfate reducing bacteria

© 2019Sulfate reducing bacteria (SRB) are often the culprits of microbiologically influenced corrosion (MIC) in anoxic environments because sulfate is a ubiquitous oxidant. MIC of carbon steel caused by SRB is the most intensively investigated topic in MIC because of its practical importance. It is also because biogenic sulfides complicate mechanistic SRB MIC studies, making SRB MIC of carbon steel is a long-lasting topic that has generated considerable confusions. It is expedient to think that biogenic H2S secreted by SRB acidifies the broth because it is an acid gas. However, this is not true because endogenous H2S gets its H+ from organic carbon oxidation and the fluid itself in the first place rather than an external source. Many people believe that biogenic H2S is responsible for SRB MIC of carbon steel. However, in recent years, well designed mechanistic studies provided evidence that contradicts this misconception. Experimental data have shown that cathodic electron harvest by an SRB biofilm from elemental iron via extracellular electron transfer (EET) for energy production by SRB is the primary cause. It has been demonstrated that when a mature SRB biofilm is subjected to carbon source starvation, it switches to elemental iron as an electron source and becomes more corrosive. It is anticipated that manipulations of EET related genes will provide genetic-level evidence to support the biocathode theory in the future. This kind of new advances will likely lead to new gene probes or transcriptomics tools for detecting corrosive SRB strains that possess high EET capabilities