Vacuolar H+-ATPase and plasma membrane H+-ATPase contribute to the tolerance against high-pressure carbon dioxide treatment in Saccharomyces cerevisiae

Temperature-dependency on the inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles

Temperature-dependency on cell membrane injury and inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles (MBCO₂) was investigated. The number of surviving S. pastorianus cells after MBCO₂ treatment detected with yeast and mould agar (YMA, an optimum agar) was higher than that with YMA adding 2.5 g/L sodium chloride and yeast nitrogen base agar (a minimum agar). However, the decrease of the surviving number by thermal treatment was not changed among above agars used. The fluorescence polarization (FP), which indicated the phase transition of the membrane of S. pastorianus cells treated with MBCO₂ increased with increasing temperature. The activity of the alkaline phosphatase (AP), a periplasmic enzyme, in S. pastorianus cells after MBCO₂ and thermal treatments increased with the FP but was reduced by further increasing temperature. The FP and AP activities after MBCO₂ treatment increased at a temperature lower than the temperature of the thermal treatment. In addition, intracellular pH of S. pastorianus decreased by the MBCO₂ treatment at lower temperature with increasing pressure. Therefore, it was revealed that phase transition of the cell membrane and inactivation of S. pastorianus was caused by MBCO₂ treatment at lower temperature than thermal treatment and that the effect was induced by the dissolved CO₂ and increased with increasing pressure.

Supercritical CO2 technology: The next standard sterilization technique?

Sterilization of implantable medical devices is of most importance to avoid surgery related complications such as infection and rejection. Advances in biotechnology fields, such as tissue engineering, have led to the development of more sophisticated and complex biomedical devices that are often composed of natural biomaterials. This complexity poses a challenge to current sterilization techniques which frequently damage materials upon sterilization. The need for an effective alternative has driven research on supercritical carbon dioxide (scCO₂) technology. This technology is characterized by using low temperatures and for being inert and non-toxic. The herein presented paper reviews the most relevant studies over the last 15 years which cover the use of scCO₂ for sterilization and in which effective terminal sterilization is reported. The major topics discussed here are: microorganisms effectively sterilized by scCO₂, inactivation mechanisms, operating parameters, materials sterilized by scCO₂ and major requirements for validation of such technique according to medical devices' standards.

Studies on formation, control and application of biofilm formed by food related microorganisms

Biofilms are sessile microbial aggregates on the interfaces, and they were usually considered as microbial contamination sources in medical care and various industries. We studied the control and application of biofilms formed by food-related microorganisms, and mechanism of the biofilm formation was also investigated. We studied the biofilm formation in mixed cultures using various combinations of two strains of food-related microorganisms. There were various microorganisms that showed decreased or increased biofilm formation in the mixed culture in comparison with that in a single culture. Biofilm formed by lactic acid bacteria and yeast isolated from traditional fermented food, Fukuyama pot vinegar, exhibited unique feature in that structure and formation mechanism, and expected to be used as an immobilized microorganism in fermentation production. Here our studies on the control and application of biofilms and the mechanisms of its formation were described.

Acid resistance contributes to the high-pressure carbon dioxide resistance of Escherichia coli K-12

Effect of deletion of acid resistant genes of E. coli on the high-pressure carbon dioxide (HPC) resistance was investigated. Genes coding amino acid decarboxylases, such as lysine, arginine, and glutamate decarboxylase, were found to contribute to HPC resistance. Protonophore-treated cells showed hypersensitivity to HPC, confirming that HPC induced cytoplasm acidification and exerted severe damage on cells by intrusion of gaseous carbon dioxide into cytoplasm.

The effect of low-pressure carbonation on the heat inactivation of Escherichia coli

The heat inactivating effect of low-pressure carbonation (LPC) at 1 MPa against Escherichia coli was enhanced to 3.5log orders. This study aimed to investigate the mechanisms of this increase in heat inactivation efficiency. The increased inactivation ratio was found to be the result of LPC-induced heat sensitization. This sensitization was not due to any physical damage to the cells as a result of the treatment. Following the depletion of intracellular ATP, the failure of the cells to discard protons caused an abnormal decrease in the intracellular pH. However, in the presence of glucose, the inactivation ratio decreased. In addition, a further increase in inactivation of more than 2log orders occurred in the presence of the protein synthesis inhibitor chloramphenicol. Hence, the decreased heat resistance of E. coli under LPC was most likely due to a depletion of intracellular ATP and a decreased capacity for protein synthesis.

Effects of high-pressure carbon dioxide on proteins and DNA in Escherichia coli

Protein changes in Escherichia coli, when subjected to high-pressure carbon dioxide (HPCD) at 10 MPa and 3 °C for 5-75 min, were assessed using the Bradford method, 2D electrophoresis (2-DE) and liquid chromatography-electrospray ionization-MS-MS (LC-ESI-MS-MS). The changes in DNA in E. coli under the same conditions were also investigated by using flow cytometry with propidium iodide and acridine orange, agarose gel electrophoresis (AGE) and the comet assay. The results showed that HPCD induced leakage loss of the proteins and DNA of E. coli as a function of treatment time. With regard to the protein changes, 182 proteins in the 2-DE profile were not found in the HPCD-treated E. coli. Among 20 selected protein spots exhibiting significant changes in intensity, 18 protein spots were identified as 15 known proteins and two as hypothetical proteins. These proteins were involved in cell composition, energy metabolism pathways, nucleic acid metabolism, global stress regulation and general metabolism. The DNA denaturation of E. coli induced by HPCD was demonstrated in this study for the first time to our knowledge, and the denaturation was enhanced by increasing treatment time. However, HPCD did not cause DNA degradation, as suggested by both AGE analysis and the comet assay.

Phenotypic heterogeneity can enhance rare-cell survival in 'stress-sensitive' yeast populations

Individual cells within isogenic microbial cultures exhibit phenotypic heterogeneity, an issue that is attracting intense interest. Heterogeneity could confer benefits, in generating variant subpopulations that may be better equipped to persist during perturbation. We tested this hypothesis by comparing the survival of wild-type Saccharomyces cerevisiae with that of mutants which are considered stress-sensitive but which, we demonstrate, also have increased heterogeneity. The mutants (e.g. vma3, ctr1, sod1) exhibited the anticipated sensitivities to intermediate doses of nickel, copper, alkaline pH, menadione or paraquat. However, enhanced heterogeneity meant that the resistances of individual mutant cells spanned a broad range, and at high stress occasional-cell survival in most of these populations overtook that of the wild type. Green fluorescent protein (GFP) reporter studies showed that this heterogeneity-dependent advantage was not related to perturbation of buffered gene expression. Deletion strain screens combined with other approaches revealed that vacuolar alkalinization resulting from loss of Vma-dependent vacuolar H(+)-ATPase activity was not the cause of vma mutants' net stress sensitivities. An alternative Vma-dependent resistance mechanism was found to suppress an influence of variable vacuolar pH on the metal resistances of individual wild-type cells. In addition to revealing new mechanisms of heterogeneity generation, the results demonstrate experimentally a benefit under adverse conditions that arises specifically from heterogeneity, and in populations conventionally considered to be disadvantaged.