Amplifiable DNA from gram-negative and gram-positive bacteria by a low strength pulsed electric field method

Effect of Pulsed Electric Field (PEF) on Bacterial Viability and Whey Protein in the Processing of Raw Milk

There is growing concern regarding the nutritional value of processed food products. Although thermal pasteurization, used in food processing, is a safe method and is widely applied in the food industry, food products lack quality and nutritional value because of the high temperatures used during pasteurization. In this study, the effect of pulsed electric field (PEF) processing on whey protein content and bacterial viability in raw milk was evaluated by changing the PEF strength and number of pulses. For comparison, traditional pasteurization techniques, such as low-temperature long-time (LTLT), ultra-high temperature (UHT), and microfiltration (MF), were also tested for total whey protein content, bacterial activity, and coliforms. We found that, after treatment with PEF, a significant decrease in total bacterial viability of 2.43 log and coliforms of 0.9 log was achieved, although undenatured whey protein content was not affected at 4.98 mg/mL. While traditional pasteurization techniques showed total bacterial inactivation, they were detrimental for whey protein content: β-lactoglobulin was not detected using HPLC in samples treated with UHT. LTLT treatment led to a significant decrease of 75% in β-lactoglobulin concentration; β-lactoglobulin content in milk samples treated with MF was the lowest compared to LTLT and UHT pasteurization, and ~10% and 27% reduction was observed.

Shock waves associated with electric pulses affect cell electro-permeabilization

New features of cell electro-permeabilization are obtained by using high field (several tens of kV/cm) with short (sub-microsecond, nanosecond) pulse duration. Arcing appears as a main safety problem when air gaps are present between electrodes. A new applicator design was chosen to obtain a closed chamber where high field pulses could be delivered in a safe way with very short pulse duration. The safety issue of the system was validated under millisecond, microsecond and nanosecond pulses. The closed chamber applicator was then checked for its use under classical electro-mediated permeabilization and electro-gene transfer (EGT). A 20 times decrease in gene expression was observed compared with classical open chambers. It was experimentally observed that shock waves were present under the closed chamber configuration of the applicator. This was not the case with an open chamber design. Electropulsation chamber design plays a role on pulsing conditions and in the efficiency of gene electro transfer.

Microfluidic electroporation for cellular analysis and delivery

Electroporation is a simple yet powerful technique for breaching the cell membrane barrier. The applications of electroporation can be generally divided into two categories: the release of intracellular proteins, nucleic acids and other metabolites for analysis and the delivery of exogenous reagents such as genes, drugs and nanoparticles with therapeutic purposes or for cellular manipulation. In this review, we go over the basic physics associated with cell electroporation and highlight recent technological advances on microfluidic platforms for conducting electroporation. Within the context of its working mechanism, we summarize the accumulated knowledge on how the parameters of electroporation affect its performance for various tasks. We discuss various strategies and designs for conducting electroporation at the microscale and then focus on analysis of intracellular contents and delivery of exogenous agents as two major applications of the technique. Finally, an outlook for future applications of microfluidic electroporation in increasingly diverse utilities is presented.

Genomic DNA extraction from cells by electroporation on an integrated microfluidic platform

The vast majority of genetic analysis of cells involves chemical lysis for release of DNA molecules. However, chemical reagents required in the lysis interfere with downstream molecular biology and often require removal after the step. Electrical lysis based on irreversible electroporation is a promising technique to prepare samples for genetic analysis due to its purely physical nature, fast speed, and simple operation. However, there has been no experimental confirmation on whether electrical lysis extracts genomic DNA from cells in a reproducible and efficient fashion in comparison to chemical lysis, especially for eukaryotic cells that have most of the DNA enclosed in the nucleus. In this work, we construct an integrated microfluidic chip that physically traps a low number of cells, lyses the cells using electrical pulses rapidly, then purifies and concentrates genomic DNA. We demonstrate that electrical lysis offers high efficiency for DNA extraction from both eukaryotic cells (up to ∼36% for Chinese hamster ovary cells) and bacterial cells (up to ∼45% for Salmonella typhimurium) that is comparable to the widely used chemical lysis. The DNA extraction efficiency has dependence on both the electric parameters and relative amount of beads used for DNA adsorption. We envision that electroporation-based DNA extraction will find use in ultrasensitive assays that benefit from minimal dilution and simple procedures.

Non-disruptive release of Pseudomonas putida proteins by in situ electric breakdown of intact cells

Analysis of the native proteome of bacterial cells typically involves physical procedures (sonication, French press) and/or biochemical methods (treatment with lysozyme, osmotic shock etc.) to break open the bacteria to yield a soluble protein fraction. Such procedures are not only time consuming, but they change bacterial physiology during manipulation and affect labile post-translational modifications such as His-P bonds. In this work, we document the efficacy of the dielectric breakdown of live bacteria for releasing and delivering the protein contents of intact cells directly into a non-denaturing gel system. By means of such an in situ electrophoresis, the protein pool enters the separation medium without any manipulation of the cells other than being exposed to a moderate electric voltage. To validate the method we have followed the fate of the two forms of the PtsN (EIIA(Ntr)) protein of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) of Pseudomonas putida through the various stages of the procedure. Apart of detecting the corresponding polypeptides, we show that this procedure releases the bulk of the proteome while keeping unharmed the phosphorylation state of EIIA(Ntr) as it was present in the cells prior to applying the electric field. The method is applicable to other bacteria as well.

Effect of low-voltage static electric field on growth of Esoherichia coli

AIM: To study the influence of static electric field with different intensities on the growth of Esoherichia coli.

METHODS: The static electric field of 3 and 24 volt were used upon the big tubes (Ф = 30 mm) in which E. coli were cultured. The optical density and bacterial colony numbers were measured during the growth process of E. coli. Meanwhile, the morphology of E. coli under the action of 24-volt static electric field was observed by scanning electron microscopy (SEM) comparatively analyzed with the control group.

RESULTS: The growth of E. coli obviously restrained during the prophase of culturing under the experiment conditions. Stable growth period of E. coli was advanced 2 and 4 hours under the action of static electric fields of 3 and 24 volt, respectively. E. coli appeared the second logarithm growth period 6-8 h after the first stable period started. That was the growth remediation of bacteria. And in the experimental conditions, the intensity of static electric field was in inverse relation with the restoring speed of E. coli. In addition, the morphological distortion of E. coli was found under the SEM.

CONCLUSION: The external low-voltage static electric field has inhibitory effect on the growth of E. coli.

Mechanisms underlying the impact of humic acids on DNA quantification by SYBR Green I and consequences for the analysis of soils and aquatic sediments

DNA quantification of soils and sediments is useful for the investigation of microbial communities and for the acquisition of their genomes that are exploited for the production of natural products. However, in such samples DNA quantification is impaired by humic acids (HA). Due to its lack of specificity and sensitivity, UV spectrophotometry cannot be applied. Consequently, fluorimetric assays applying Hoechst (H) 33258 or PicoGreen (PG) are used. Here, we investigated the SYBR Green I (SG) assay, which was also affected by HA, but was found to be 25- and 1.7-fold more sensitive compared to the H 33258 and PG assays, respectively. Spectrophotometric, fluorimetric and quenching studies as well as gel mobility shift assays suggested that the effect of HA on the SG assay was based on an inner filter effect, collisional quenching and binding of SG to HA. As to the latter finding, the standard 6250-fold dilution of the SG reagent was optimised to a 2000-fold dilution. Although the sensitivity of the optimised SG assay was reduced by a factor of 1.3, the interfering effect of HA could be reduced up to 22-fold. A significant reduction of HA interferences by lowering the pH of the assay was not observed. Finally, the performance of the modified SG assay and the corresponding evaluation methods were verified by the determination of DNA recoveries and concentrations of standards and environmental samples in comparison to the PG assay.