Cytochrome oxidase activity and confocal laser scanning microscopic analysis of the hamster submandibular gland using microwave irradiated fixation

A comparative study on the structure of Saccharomyces cerevisiae under nonthermal technologies: high hydrostatic pressure, pulsed electric fields and thermo-sonication

Nonthermal technologies are becoming more popular in food processing; however, little detailed research has been conducted on the study of the lethal effect of these technologies on certain microorganisms. Saccharomyces cerevisiae is a yeast related to spoilage of fruit products such as juices; novel technologies have been explored to inactivate this yeast. Three nonthermal technologies, high hydrostatic pressure (HHP), pulsed electric fields (PEF) and thermo-sonication (TS), were used to evaluate and to compare the structural damage of yeast cells after processing. Processing conditions were chosen based on previous experiments to ensure the death of cells; HHP was conducted at 600 MPa for 7 min (room temperature, 21 °C); for PEF, 30.76 kV/cm at 40 °C and 21 pulses (2 μs each), and finally for TS the conditions were 120 μm, 60 °C and 30 min in continuous and pulsed modes; all treatments were applied in apple juice. Cells were prepared for electron microscopy using an innovative and short microwave assisted dehydration technique. Scanning electron microscopy showed the degree of damage to the cells after processing and illustrated the important and particular characteristics of each technology. Cells treated with high hydrostatic pressure showed a total disruption of the cell membrane, perforation, and release of the cell wall; scars were also observed on the surface of the pressurized cells. PEF treated cells showed less superficial damage, with the main changes being the deformation of the cells, apparent fusion of cells, the formation of pores, and the breakdown of the cell wall in some cells. Finally, the thermo-sonicated cells showed a similar degree of cellular damage to their structure regardless of whether the TS was applied continuously or pulsed. The main characteristics of cellular death for this technology were the erosion and disruption of the cellular membrane, formation of orifices on the surface, lysis of cells causing the release of intracellular contents, roughness of the cell membrane, and displacement of cell debris to the surface of other cells. This study confirms some theories about cell inactivation and presents new and detailed results about nonthermal technologies, but also shows that after using the above mentioned conditions, recovery of cells, specifically those that are pressurized and thermo-sonicated, it is not possible to do it following the high extent of damage observed in the entire population. Furthermore, a faster methodology that was used in sample preparation for electron microscopy provided high quality resolution images, allowing closer study of the detail of structural lethal effects on treated cells.

Metaproteomic and metagenomic analyses of defined oceanic microbial populations using microwave cell fixation and flow cytometric sorting

A major obstacle in the molecular investigation of natural, especially oceanic, microbial cells is their adequate preservation for further land-based molecular analyses. Here, we examined the use of microwaves for cell fixation before high-speed flow cytometric sorting to define the metaproteomes and metagenomes of key microbial populations. The microwave fixation procedure was established using cultures of Synechococcus cyanobacteria, the photosynthetic eukaryote Micromonas pusilla and the gammaproteobacterium Halomonas variabilis. Shotgun proteomic analyses showed that the profile of microwave-fixed and -unfixed Synechococcus sp. WH8102 cells was the same, and hence proteome identification of microwave-fixed sorted cells by nanoLC-MS/MS is possible. Microwave-fixed flow-sorted Synechococcus cells can also be successfully used for whole-genome amplification and fosmid library construction. We then carried out successful metaproteomic and metagenomic analyses of microwave-fixed Synechococcus cells flow sorted from concentrates of microbial cells, collected in the North Atlantic Ocean. Thus, the microwave fixation procedure developed appears to be useful for molecular studies of microbial populations in aquatic ecosystems.

Microwave antigen retrieval blocks endogenous peroxidase activity in immunohistochemistry

Endogenous peroxidase activity blocking is one of the most critical steps for a successful immunostaining. A traditional procedure for this purpose was to use diluted hydrogen peroxide (H2O2) solution to gain a better visualization. Our current study was designed to test if the conventional antigen retrieval (AR) step with microwave oven could also inhibit endogenous peroxidase. Tissue sections were treated in following different ways before incubating with 3, 3' diaminobenzidine tetrahydrochloride reaction mixture: (1) microwave alone, (2) 0.3% or 3% of H2O2 before AR, or (3) 0.3% or 3% of H2O2 after AR. Surprisingly, we found that all different treatments completely eliminated the endogenous enzymatic activity, mostly in eosinophils and erythrocytes, suggesting that microwave exposure itself is able to block the endogenous peroxidase. The results were validated in most gastrointestinal tract mucosa from human and some tissues from mice, including blood enriched tissues, such as liver and spleen. We have obtained perfect immunostaining without any H2O2 blocking procedure. On the basis of our observation, we conclude that blockage of endogenous peroxidase with H2O2 in immunostaining could be omitted and replaced by microwave oven heating.

Structural and antigenic preservation of plant samples by microwave-enhanced fixation, using dedicated hardware, minimizing heat-related effects

We explored the use of microwave technology in fixation with the objective of achieving quicker fixation regimes, lower concentrations of toxic and volatile reagents, and enhanced antigen detection. We used a modified domestic microwave oven (900 W) and a low-power (5 W) microwave bench. The work was done on plant materials. The oven was supplemented with a cooling device, a stirring system, and a record of the sample temperature and the time of effective irradiation. The sample, immersed in a fixative solution of 1% paraformaldehyde (PFA) in PBS, was irradiated for only 10 minutes. The sample temperature did not exceed 37 degrees C. In these mild conditions, the quality of the (ultra)structural preservation of the samples, morphometrically assessed, was at the same level as obtained with the same fixative, using conventional methods. On the contrary, samples fixed in the same conditions without irradiation showed a poor structural preservation. The antigenic preservation of the irradiated samples was excellent, since the labeling levels of two nucleolar proteins, detected by immunogold, were three times higher than in conventionally fixed samples. In the so-called microwave bench, the pathway of microwaves is guided, so that low-power microwaves directly hit the sample and there is no dispersion of energy. Temperature of fixative did not increase after microwave irradiation. Fixation in the bench with either 4% PFA, or 1% PFA, for 20 minutes resulted in structural preservation of samples similar in quality as obtained with conventional fixation and in a similar or better level of antigen preservation. Therefore, controlling temperature and effective irradiation is crucial in order to obtain optimal structural and antigen preservation with microwave-enhanced fixation. The dramatic differences observed between microwave-irradiated samples and samples fixed in the same conditions without irradiation, strongly support the existence of specific effects of microwaves on fixation, independent from the mere heating of the samples.