Gamma-irradiated Aspergillus conidia show a growth curve with a reproductive death phase

In this study, we evaluated the effects of gamma irradiation on the germination of Aspergillus conidia and mycelial growth using microscopy and predictive microbiological modeling methods. A dose of 0.4 kGy reduced the germination rate by 20% compared to the untreated control, indicating interphase death due to the high radiation dose. The number of colonies formed (5.5%) was lower than the germination rate (69%), suggesting that most colonies died after germination. Microscopic observations revealed that mycelial elongation ceased completely in the middle of the growth phase, indicating reproductive death. The growth curves of irradiated conidia exhibited a delayed change in the growth pattern, and a decrease in slope during the early stages of germination and growth at low densities. A modified logistic model, which is a general purpose growth model that allows for the evaluation of subpopulations, was used to fit the experimental growth curves. Dose-dependent waveform changes may reflect the dynamics of the subpopulations during germination and growth. These methods revealed the occurrence of two cell death populations resulting from gamma irradiation of fungal conidia and contribute to the understanding of irradiation-induced cell death in fungi.

Lethal and mutagenic effects of different LET radiations on Bacillus subtilis spores

New, useful microorganism resources have been generated by ionizing radiation breeding technology. However, the mutagenic effects of ionizing radiation on microorganisms have not been systematically clarified. For a deeper understanding and characterization of ionizing radiation-induced mutations in microorganisms, we investigated the lethal effects of seven different linear energy transfer (LET) radiations based on the survival fraction (SF) and whole-genome sequencing analysis of the mutagenic effects of a dose resulting in an SF of around 1% in Bacillus subtilis spores. Consequently, the lower LET radiations (gamma [surface LET: 0.2 keV/µm] and 4He2+ [24 keV/µm]) showed low lethality and high mutation frequency (MF), resulting in the major induction of single-base substitutions. Whereas higher LET radiations (12C5+ [156 keV/µm] and 12C6+ [179 keV/µm]) showed high lethality and low MF, resulting in the preferential induction of deletion mutations. In addition, 12C6+ (111) ion beams likely possess characteristics of both low- and high-LET radiations simultaneously. A decrease in the relative biological effectiveness and an evaluation of the inactivation cross section indicated that 20Ne8+ (468 keV/µm) and 40Ar13+ (2214 keV/µm) ion beams had overkill effects. In conclusion, in the mutation breeding of microorganisms, it should be possible to regulate the proportions, types, and frequencies of induced mutations by selecting an ionizing radiation of an appropriate LET in accordance with the intended purpose.

High-Resolution Detection of Translocation of Oral Bacteria to the Gut

Ectopic enrichment of oral microbes in the gut is a notable alteration in gut microbial balance. These microbes are likely delivered from the oral cavity with saliva and food; however, evidence of oral-gut microbial transmission is insufficient and needs further investigation. In this observational study, we examined 144 pairs of saliva and stool samples collected from community-dwelling adults to verify the oral-gut microbial link and identify the relevant influencing factors on the increased abundance of oral microbes within the gut. The bacterial composition of each sample was determined using PacBio single-molecule long-read sequencing of the full-length 16S ribosomal RNA gene and amplicon sequence variant (ASV) analysis. Although the bacterial compositions of salivary and gut microbiota were distinctly different, at least 1 ASV was shared between salivary and gut microbiota in 72.9% of subjects. Shared ASVs accounted for 0.0% to 63.1% (median 0.14%) of the gut microbiota in each subject and frequently included abundant Streptococcus salivarius and Streptococcus parasanguinis. Their total relative abundance in the gut was significantly higher in older subjects or those with dental plaque accumulation. The gut microbiota with ≥5% of shared ASVs displayed a higher abundance of Streptococcus, Lactobacillus, and Klebsiella and a lower abundance of Faecalibacterium, Blautia, Megamonas, and Parabacteroides. Our study presents evidence for the translocation of oral bacteria to the gut in community-dwelling adults and suggests that aging and dental plaque accumulation contribute to an increased abundance of oral microbes in the gut, which might be relevant to the compositional shift in the gut commensals.

[Detection of Gamma-Ray Irradiation History of Dried Plant-Based Foods via the Analysis of 5,6-Dihydrothymidine]

Irradiation is widely used worldwide to sterilize and kill insects in food, and prevent the germination of agricultural products. However, in Japan, food irradiation is prohibited except to prevent potato sprouting. Herein, 5,6-dihydrothymidine (DHdThd) residue-a damaged nucleoside generated from the thymidine (dThd) residue in DNA contained in food upon irradiation-was used as a detection indicator. Eight dried plant-based food samples were gamma ray-irradiated in the range from 3.2 to 8.3 kGy. Subsequently, DNA was extracted from the irradiated sample and digested into nucleosides by the three enzymes, and the test solution was analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Evidently, in all samples, the concentration ratio of DHdThd to dThd in the test solution (DHdThd/dThd) was dependent on the irradiation dose; moreover, during storage under frozen conditions for at least 890 d post-irradiation, this concentration ratio was equal to that immediately after irradiation. The irradiation histories of the eight types of dried plant-based food samples were correctly detected.

Theory and application of growth delay analysis of colony formation for evaluation of injured population of the stressed fungal conidia

A new concept of injured population assessment is proposed, in which the size of the injured population in stressed mold spores is evaluated by analyzing the colony formation process on a solid agar medium. In this method, a small paper disc containing mold spores is placed on a subculture agar plate, and the linear increase in the radius of the colony formed by development from the spore is measured over time. Then, the principle of the previously reported growth delay analysis (GDA) method originally using a liquid medium is applied to obtain the integrated viable ratio (IV) of the stressed population from the delay time relative to the growth of the unstressed population. On the other hand, the viable ratio (V) to the initial value as the colony count obtained with the stressed culture is obtained; the difference between the logarithms of V and IV is determined as the log number of the injured population. Applying this analysis method to heated spores of Cladosporium sphaerospermum, we determined the size of the injured population that occurred. This method was considered to be effective as a new method for quantifying injured populations using a solid medium.

Excessive ultraviolet C irradiation causes spore protein denaturation and prohibits the initiation of spore germination in Bacillus subtilis

Ultraviolet (UV) -C is widely used to kill bacteria as it damages chromosomal DNA. We analyzed the denaturation of the protein function of Bacillus subtilis spores after UV-C irradiation. Almost all of the B. subtilis spores germinated in Luria-Bertani (LB) liquid medium, but the colony-forming unit (CFU) of the spores on LB agar plates decreased to approximately 1/10³ by 100 mJ/cm² of UV-C irradiation. Some of the spores germinated in LB liquid medium under phase-contrast microscopy, but almost no colonies formed on the LB agar plates after 1 J/cm² of UV-C irradiation. The fluorescence of the green fluorescent protein (GFP) -fused spore proteins, YeeK-GFP, YeeK is a coat protein, decreased following UV-C irradiation of over 1 J/cm², while that of SspA-GFP, SspA is a core protein, decreased following UV-C irradiation of over 2 J/ cm², respectively. These results revealed that UV-C affected on coat proteins more than core proteins. We conclude that 25 to 100 mJ/cm² of UV-C irradiation can cause DNA damage, and more than 1 J/cm² of UV-C irradiation can cause the denaturation of spore proteins involved in germination. Our study would contribute to improve the technology to detect the bacterial spores, especially after UV sterilization.

Different patterns of germination inhibition by carvacrol and thymol in Bacillus subtilis spores

This study aimed to clarify how the phenolic monoterpene carvacrol and its structural isomer thymol both as essential oil components (EOCs) inhibit the germination of Bacillus subtilis spore. Germination was evaluated by the OD₆₀₀ reduction rate in a growth medium and phosphate buffer containing either l-alanine (l-Ala) system or l-asparagine, d-glucose, d-fructose plus KCl (AGFK) system. The germination of the wild-type spores in the Trypticase Soy broth (TSB) was found to be greatly inhibited by thymol than by carvacrol. Such a difference in the germination inhibition was confirmed by the dipicolinic acid (DPA) release from germinating spores in the AGFK buffer system, but not in the l-Ala system. Similar to the wild-type spores, no difference in the inhibitory activity between the EOCs was also indicated with the gerB, gerK-deletion mutant spores in the l-Ala buffer system and the above substantial difference was also done with the gerA-deleted mutant spores in the AGFK. Fructose was found to release spores from the EOC inhibition and inversely even stimulated. Increased concentrations of glucose and fructose partially suppressed the germination inhibition by carvacrol. The results obtained should contribute to the elucidation of the control effects of these EOCs on bacterial spores in foods.

Preparation of High-quality Oil from Vegetable Oil with High-free Fatty Acid (FFA) Content Using an Ammonia/Methanol Solution

There are significant concerns regarding the quality of vegetable oils in the food and biofuel industries. In this study, we explored the preparation of high- quality oil from high-free fatty acid (FFA) vegetable oil using an ammonia/MeOH solvent as an alkali base. Among the six tested solvents, MeOH was the most suitable for the separation of the oil and FFAs. Among the three alkali bases, ammonia enhanced the miscibility of FFAs in MeOH by forming ammonium salts. The amounts of FFAs in the upper layer and oil in the lower layer were positively correlated (r = 0.9348 and 0.9617, respectively) with MeOH. With increasing MeOH concentration, the amount of oil in the lower layer increased along with the FFAs in the upper layer. Using the molar ratio of ammonia to FFA 1:1 and the ratio (v/w) of MeOH to oil 4:3, 91.6% FFAs and 97.8% oil in the upper and lower layers, respectively, were produced from 50% FFA oil. Using a relational expression of FFAs and oil in the upper layer, 97.1% FFAs and 99.6% oil in each layer was obtained from 10% FFA oil. The oil in the lower layer was further purified by extraction with MeOH. This method is easy and efficient for the separation and purification of oil, accompanied by the reuse of reagents with almost no loss of raw materials.

Evaluation of distinct modes of oxidative secondary injury generated in heat-treated cells of Escherichia coli with solid/liquid and complex/semi-synthetic media sets

AIMS

To characterize and evaluate oxidative secondary injury generated in heat-treated Escherichia coli cells during recovery cultivation either on agar or in a broth of a semi-synthetic enriched M9 (EM9) medium and a complex Luria broth (LB) medium with different types of antioxidants.

METHODS AND RESULTS

E. coli cells grown in the EM9 and LB broth were heated at 50^o C in a buffer (pH7.0). Heated cells were recovered on the same kind of agar medium as that used for growth, with or without different antioxidants. Although these antioxidants mostly protected the cells from oxidative secondary injury on the recovery media, sodium thiosulfate and sodium pyruvate were most protective on EM9 and LB agars, respectively. Determination of viability using the most probable number and growth delay analysis methods showed significant reductions in the protective effects of antioxidants in the EM9 and LB media.

CONCLUSION

Oxidative secondary injury generated in heated E. coli cells was found to be qualitatively and quantitatively diverse under cellular and environmental conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results suggest that different modes of oxidation should be considered in viability determination and injured cell enumeration of heat-treated cells.

Low Temperature Heating-Induced Death and Vacuole Injury in Cladosporium sphaerospermum Conidia

The mechanism of thermal death of mold conidia has not been understood in detail. The purpose of this study is to analyze the death kinetics of heated conidia of Cladosporium sphaerospermum and to ascertain the expectant cell injury responsible for the death. The death of the dormant (resting) conidia of Cladosporium sphaerospermum was examined at temperatures of between 43 and 54℃ with the conventional colony count method. The death reaction apparently followed the first order kinetics, but the Arrhenius plot of the death rate constant demonstrated seemingly a break. The linearity at temperatures higher than that at the break was lost at lower temperatures, suggesting the involvement of an unusual mechanism in the latter temperatures. In the cell morphology, we observed with quinacrine staining the vacuole rupture at a lower temperature but not at a high temperature. Interestingly, the vacuole rupture by low-temperature heating was found to correlate with the viability loss. Furthermore, active protease originally locating in vacuoles was detected in the cytoplasm of the conidia after heated at a low temperature. The results obtained suggest the involvement of potent autophagic cell death induced by low temperature heating of C. sphaerospermum conidia.

Trehalose accumulation and radiation resistance due to prior heat stress in Saccharomyces cerevisiae

In this study, we examined the accumulation of trehalose, a stress-responsive substance, upon gamma-ray irradiation by evaluating the cause of trehalose accumulation and the development of gamma-ray resistance through intracellular trehalose accumulation. Saccharomyces cerevisiae cells cultured to the logarithmic growth phase were irradiated with gamma rays, and the intracellular trehalose content was measured. However, trehalose was not detectable. The yeast cells with trehalose accumulation caused by pre-treatment at 40 °C were irradiated with gamma rays, and the resistance of these cells to gamma radiation was compared with that of cells without heat treatment. Trehalose accumulation resulted in gamma-ray resistance and suppressed the increase in reactive oxygen species, lipid peroxidation, and DNA double-strand break production in yeast cells. The tests were also performed with a trehalose-6-phosphate-synthase (TPS1)-deficient mutant strain (Δtps1) unable to synthesize trehalose, and the results revealed that TPS1 was involved in protection against oxidative stress.

Detection Time Distribution of Microcolonies Formed by Individual Heat-Injured Cells of Escherichia coli

The microcolony formation at 30℃ on an enriched minimal salts agar plates by individual Escherichia coli cells heated at 50℃ was monitored with a time-lapse shadow image analysis system, MicroBio μ3D^TM AutoScanner. While the time course of microcolony count detected every half an hour for the unheated cells seemingly demonstrated a normal distribution, that for the heated cell population demonstrated totally the growth delay probably resulting from cell injury and also interestingly distributed in its rather deformed pattern with a tailing. Those patterns of the cumulative counts of appearing microcolonies during the post-heating cultivation period were expressed in three different mathematical models. This approach may be proposed as a rapid cultivation method predictable for enumeration of viable and repairable injured cells in practical use.

The characterization of tocols in different plants parts of six Japanese rice cultivars relating to their UVB-sensitivity

There has been significant interest in the photosensitivity, or photo-resistance, of Japanese rice cultivars, which synthesize tocols (Vitamin E), a class of phytochemicals including tocol derivatives tocopherol (T) and tocotrienol (T3). In the present study, the distribution of tocols in the leaves, seeds, stems, and roots of six Japanese rice cultivars was investigated. The relationship between the different tocols in cultivars and their ultraviolet B sensitivity index (USB-SI) was analyzed. The leaves contained the highest average total amount of tocols at 230 μg.fresh-g^-1, followed by seeds, stems, and roots. In leaves and stems, the most abundant component was α-T which was more than 85%. On the other hand, the tocols in seeds were 38% δ-T3, 32% α-T, and 20% α-T3. The tocols in roots were 55% α-T, 14% γ-T, and 13% δ-T3. The total tocol content in four plant parts exhibited a negative correlation (P < 0.05) in stem and root, and a negative relationship (r < -0.70) with the UVB-SI of the cultivars, suggesting that the total tocol contents were closely related to the resistance to UVB in Japanese rice plants.

Biological effects of low-dose γ-ray irradiation on chromosomes and DNA of Drosophila melanogaster

While the damage to chromosomes and genes induced by high-dose radiation (HDR) has been well researched in many organisms, the effects of low-dose radiation (LDR), defined as a radiation dose of ≤100 mSv, are still being debated. Recent research has suggested that the biological effects of LDR differ from those observed in HDR. To detect the effect of LDR on genes, we selected a gene of Drosophila melanogaster, known as the multiple wing hair (mwh) gene. The hatched heterozygous larvae with genotype mwh/+ were irradiated by γ-rays of a 60Co source. After eclosion, the wing hairs of the heterozygous flies were observed. The area of only one or two mwh cells (small spot) and that of more than three mwh cells (large spot) were counted. The ratio of the two kinds of spots were compared between groups irradiated by different doses including a non-irradiated control group. For the small spot in females, the eruption frequency increased in the groups irradiated with 20-75 mGy, indicating hypersensitivity (HRS) to LDR, while in the groups irradiated with 200 and 300 mGy, the frequency decreased, indicating induced radioresistance (IRR), while in males, 50 and 100 mGy conferred HRS and 75 and 200 mGy conferred IRR. For the large spot in females, 75 mGy conferred HRS and 100-800 mGy conferred IRR. In conclusion, HRS and IRR to LDR was found in Drosophila wing cells by delimiting the dose of γ-rays finely, except in the male large spot.

Application of gamma radiation for disinfection of fungi in a large volume of historical archives damaged by flood following Typhoon Hagibis 2019, Japan: A case report

A large volume of historical archives was extensively damaged by flood water, following Typhoon Hagibis in Fukushima, Japan, in October 2019. They were rescued from the stricken area within a week, however, the prolonged exposure of paper documents to water caused severe biodegradation by fungal growth. To disinfect fungi, the paper documents were exposed to gamma radiations emitted by a source of Cobalt 60 by the industrial irradiation service. The wet paper documents were mainly contaminated with hydrophilic and cellulolytic fungi, including Trichoderma, Stachybotrys, and Fusarium; no fungi grew after irradiation. These results indicated that the average absorbed dosage from 13.1 kGy to 16.1 kGy were sufficient to disinfect paper documents heavily contaminated with fungi. In the present study, we demonstrated the successful practical use of irradiation in fungi-damaged paper documents using a commercial gamma-irradiation facility.

A Modified Double Subculture Method for the Two-Mode Injuries Evaluation in a Stressed Fungal Spore Population

In order to evaluate injury of a stressed fungal spore population, a modification of formerly presented double subculture method, which consists of both the conventional plate count method and the growth delay analysis method, was proposed. In this method, an apparent logarithmic growth kinetics was assumed and the previous kinetic model was improved to be able to estimate injured subpopulations in two different modes containing early occurring growth-independent and late occurring growth-dependent injuries, called the λ and μ injuries, respectively. Based on the kinetic theory developed here, this novel method was applied to heat-treated conidia of Cladosporium cladosporioides and these two mode injuries were evaluated.

Estimation of Irradiation Doses of Raw Beef Liver Samples using 5,6-Dihydrothymidine as an Irradiation Marker

The quantities of (5S)- and (5R)-5,6-dihydrothymidine (total DHdThd) in frozen beef liver samples were compared between those irradiated by an electron beam (EB) and those subjected to γ-irradiation. DNA extracted from the samples was enzymatically digested to nucleosides and analyzed by liquid chromatography-tandem mass spectrometry for total DHdThd and 2'-deoxythymidine (dThd). Total DHdThd was formed radiospecifically and dose-dependently and the dose-response curves of the ratio of total DHdThd to dThd (total DHdThd/dThd) were similar for both the EB- and γ-irradiated samples. The total DHdThd/dThd was stable after long-term storage (4 months) at -20 °C and the followed heat treatment in a microwave oven. The total DHdThd/dThd could be a robust marker and is equally effective at quantitating both EB- and γ-ray irradiation history. The irradiation doses of raw beef liver samples were estimated using the dose-response curves of the total DHdThd/dThd of other irradiated samples. The ratio of the estimated dose to the actual dose was 0.74-1.30 in the irradiation range of 4.67-7.62 kGy.

Periodontitis Is Associated with Chronic Obstructive Pulmonary Disease

Although they are known to share pathophysiological processes, the relationship between periodontitis and chronic obstructive pulmonary disease (COPD) is not fully understood. The aim of the present study was to test the hypothesis that periodontitis is associated with a greater risk of development of COPD, when smoking is taken into account. The analysis in a 5-y follow-up population-based cohort study was based on 900 community-dwelling Japanese adults (age: 68.8 ± 6.3 [mean ± SD], 46.0% male) without COPD aged 60 or older with at least 1 tooth. Participants were classified into 3 categories according to baseline periodontitis severity (no/mild, moderate, and severe). COPD was spirometrically determined by a fixed ratio of <0.7 for forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) and by FEV1/FVC below the lower limit of normal. Poisson regression was used to calculate the relative risk (RR) of developing COPD according to the severity of periodontitis. The population attributable fraction (PAF) was also calculated. During follow-up, 22 (2.4%) subjects developed COPD. Compared with no/mild periodontitis subjects, a significantly increased risk of COPD occurred among severe periodontitis subjects (RR = 3.55; 95% confidence interval [CI], 1.18 to 10.67), but no significant differences were observed between the no/mild and moderate categories (RR = 1.48; 95% CI, 0.56 to 3.90). After adjustment for potential confounders, including smoking intensity, the relationship between severe periodontitis and risk of COPD remained significant (RR = 3.51; 95% CI, 1.15 to 10.74). Likewise, there was a positive association of periodontitis severity with risk of COPD ( P for trend = 0.043). The PAF for COPD due to periodontitis was 22.6%. These data highlight the potential importance of periodontitis as a risk factor for COPD.

Inhibitory Effect of Spice Powders on the Development of Heated and Irradiated Bacillus subtilis Spores as Evaluated by Calorimetry

Inhibitory effects of the powders of paprika, red pepper, black pepper, sage, oregano and thyme in a solid medium after heat treatment and gamma-irradiation on the development from spore of Bacillus subtilis were examined using calorimetry. Based on the f(t) curve (Antoce et al., 1996) from the thermogram obtained, two parameters, the growth rate constant and the growth retardation time, were used to evaluate the inhibitory effect. The inhibitory effects of paprika and red pepper powders were enhanced by the spore pretreatment with heat, but not significantly with irradiation. The inhibitory enhancement by preheating depended upon the kind of spices used. Sage, oregano and thyme powders per se inhibited the development from spores completely even at a low concentration of 0.04 g/ml. Inhibitory effects of paprika and red pepper powders were obviously observed with heat treatment but not with irradiation. With black pepper powder, by contrast, substantial enhancement was neither observed with heat treatment nor gamma-irradiation. The results suggested that the addition of those spice powders might be useful in the thermal inactivation process of solid foods contaminated with Bacillus subtilis spores.

Raman optical activity of tetra-alanine in the poly(l-proline) II type peptide conformation

The poly(l-proline) II (PPII) helix is considered to be a major conformation in disordered polypeptides and unfolded proteins in aqueous solution. The PPII conformation can be identified by using Raman optical activity (ROA), which measures the different intensities of right- and left-circularly polarized Raman scattered light from chiral molecules and provides information on stereochemistry associated with vibrational motions. In the present study, we used tetra-alanine (Ala₄) as a model system, since its central amide bond adopts the PPII conformation. The predominance of the PPII conformation was supported by 11 ns molecular dynamics (MD) simulations at 300 K. The MD snapshots were used for subsequent quantum mechanical/molecular mechanical (QM/MM) calculations to compute the Raman and ROA spectra. The present MD + QM/MM analysis leads to a good agreement between the observed and simulated spectra, allowing us to assign most of the spectral features including the ROA band near 1320 cm^-1, which has been used as a marker for the PPII conformation. This positive ROA band has three components. The lower frequency component near 1310 cm^-1 arises from an internal peptide bond, whereas the higher frequency components around 1320-1335 cm^-1 appear due to N- and C-terminal peptide groups. The MD + QM/MM calculations also reproduced the electronic circular dichroism spectra of Ala₄. The present results provide a satisfactory framework for future investigations of unfolded/disordered proteins as well as peptides in solutions by chiral spectroscopic methods.

Rapid and Reliable Method for Determining Irradiation Histories of Ground Beef and Prawns by Measuring 5,6-Dihydrothymidine

A rapid and reliable method for determining irradiation histories of ground beef and prawns was developed on the basis of a method for determining the irradiation history of beef liver by liquid chromatography-tandem mass spectrometry (LC-MS/MS) of 5,6-dihydrothymidine (DHdThd). Improvements in the method included the following: (1) 50% ethanol precipitation in the DNA extraction step was conducted before the RNase step, (2) snake venom phosphodiesterase I was used for DNA digestion to boost liberation of DHdThd, and (3) a matrix-matched calibration curve was used for determining DHdThd by LC-MS/MS analysis. This method successfully determined irradiation histories of ground beef and prawns. Furthermore, a close correlation between the formation of DHdThd and 2-alkylcyclobutanones, which are an established index of irradiation histories, was observed in ground beef. DHdThd in DNA could be a promising candidate for a new index of irradiation histories of various foods.

A single-molecule assessment of the protective effect of DMSO against DNA double-strand breaks induced by photo-and γ-ray-irradiation, and freezing

Dimethyl sulfoxide (DMSO) is widely used as a cryoprotectant for organs, tissues, and cell suspension in storage. In addition, DMSO is known to be a useful free radical scavenger and a radio-protectant. To date, many in vitro assays using cultured cells have been performed for analysing the protective effect of DMSO against genomic DNA damage; however, currently it has been rather difficult to detect DNA double strand breaks (DSBs) in a quantitative manner. In the present study, we aimed to observe the extent of DNA damage by use of single molecular observation with a fluorescence microscope to evaluate DSBs induced by photo- and γ-ray-irradiation, or freeze/thawing in variable concentrations of DMSO. As a result, we found that 2% DMSO conferred the maximum protective effect against all of the injury sources tested, and these effects were maintained at higher concentrations. Further, DMSO showed a significantly higher protective effect against freezing-induced damage than against photo- and γ-ray-irradiation-induced damage. Our study provides significant data for the optimization of DNA cryopreservation with DMSO, as well as for the usage of DNA as the protective agent against the injuries caused by active oxygen and radiations.

Oral mycobiome in community-dwelling elderly and its relation to oral and general health conditions

OBJECTIVE

Oral fungal infection is generally associated with dysbiosis related to antibiotic use, immunodeficiency, or frailty. However, fungal colonization in a typical population without apparent symptoms and its associated conditions are poorly understood. In this study, oral fungal colonization in community-dwelling and independently living elderly populations was evaluated and factors affecting fungal colonization were analyzed.

SUBJECTS AND METHODS

The subjects (410; 181 males and 229 females) were 75-99 years of age; those under prior antibiotic use were excluded. Fungal populations in the saliva were evaluated by PCR-based molecular techniques. Body mass index (BMI), smoking habits, and oral health conditions were examined.

RESULTS

Salivary fungal amounts exceeded 10⁴  CFU/ml in 63 (15.4%) of 410 subjects. Candida albicans was most frequently detected (98.4%), followed by Candida glabrata (54.0%), and Candida dubliniensis (38.1%) in those subjects with fungi at 10⁴  CFU/ml or over. Fungi at 10⁴  CFU/ml or over in the presence of C. glabrata or C. dubliniensis was significantly associated with low BMI.

CONCLUSIONS

Candida albicans, C. glabrata, and C. dubliniensis dominated the oral mycobiome in Japanese community-dwelling elderly. Lower BMI might signify compromised health status and thus could result in susceptibility to specific candidiasis by C. glabrata and C. dubliniensis.

Determination of irradiation histories of raw beef livers using liquid chromatography-tandem mass spectrometry of 5,6-dihydrothymidine

A method for detecting irradiation histories of raw beef livers was developed by measuring 5,6-dihydrothymidine (DHdThd) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Liver DNA was extracted using phenol-chloroform extraction followed by precipitation in 50% ethanol. DNA was then enzymatically digested and nucleosides were purified using an OASIS MCX column. DHdThd and thymidine (dThd) contents of resulting test solutions were analyzed using LC-MS/MS. DHdThd was detected specifically after γ-irradiation. Concentration ratios of DHdThd to dThd in the test solutions increased dose-dependently after irradiation at 1.0-11.3kGy, which included the practical dose for sterilization of 2-7kGy. Dose-response curves from beef livers of individual animals almost overlapped. Thus, this method is a candidate for the detection of irradiation histories of foods from which DNA can be extracted.

Roles of Catalase and Trehalose in the Protection from Hydrogen Peroxide Toxicity in Saccharomyces cerevisiae

The roles of catalase and trehalose in Saccharomyces cerevisiae subject to hydrogen peroxide (H2O2) treatment were examined by measuring the catalase activity and intracellular trehalose levels in mutants lacking catalase or trehalose synthetase. Intracellular trehalose was elevated but the survival rate after H2O2 treatment remained low in mutants with deletion of the Catalase T gene. On the other hand, deletion of the trehalose synthetase gene increased the catalase activity in mutated yeast to levels higher than those in the wild-type strain, and these mutants exhibited some degree of tolerance to H2O2 treatment. These results suggest that Catalase T is critical in the yeast response to oxidative damage caused by H2O2 treatment, but trehalose also plays a role in protection against H2O2 treatment.

Isolation and Characterization of a Variant Manganese Resistant Strain of Saccharomyces cerevisiae

　Manganese contamination in water is one of the most serious problems in Southeast Asian countries, including Vietnam. Bioremediation using microorganisms, especially from the brewing yeast Saccharomyces cerevisiae, is expected to be a useful technique to remove manganese from contaminated water. Yeast strain S. cerevisiae BY4741 as the wild-type strain and some manganese-accumulating mutants bred from BY4741 were examined for cell growth and manganese accumulation in YPD liquid medium containing various concentrations of Mn²⁺.　Variants accumulating larger concentrations of manganese were isolated by the repeated screening of survivors in YPD media containing10mM Mn²⁺. Manganese was accumulated by the yeast cells during growth, but the growth of BY4741 was retarded with increasing Mn²⁺ concentrations and almost inhibited at 15mM Mn²⁺. One variant isolate, named IM3, showed no retardation of growth up to 15 mM Mn²⁺ and could absorb over 4-fold more manganese than the BY4741 strain. Effects of culture temperature and pH on the growth and manganese accumulation were analyzed for IM3. Maximum accumulation was shown at 30℃, pH 6.0 while the optimal growth was shown at 37℃, pH 5.0 - 7.0. Interestingly, IM3 could grow a little at pH 9.0 when manganese was added to the culture media, while it could not grow without the addition of manganese.

Antifungal Activity of Diglycerin Ester of Fatty Acids against Yeasts and Its Comparison with Those of Sucrose Monopalmitate and Sodium Benzoate

The antifungal activities of diglycerin monoester of fatty acids (DGCs), which have been employed as food emulsifiers, were examined against three yeasts, Saccharomyces cerevisiae, Candida albicans and Candida utilis and were compared with those of sucrose monoester of palmitic acid (SC16) as another type of emulsifier and sodium benzoate (SB) as a weak acid food preservative. When the minimum growth inhibitory concentrations (MICs) of diglycerin monolaurate (DGC12) against these yeasts were determined 2 d after incubation in YM broth at pH5.0, they were relatively low, being 0.01% (w/v), for both S. cerevisiae and C. utilis, whereas was high, being 4.0% (w/v), for C. albicans. On the contrary, the MICs of sucrose monopalmitate (SC16) were high, being 3.0 and 4.0% (w/v), for the former two yeasts, respectively, but 0.6% (w/v) for the last yeast. In contrast to these emulsifiers, the MICs of sodium benzoate (SB) were similar independently upon the yeast strain, being in order 0.4, 0.3 and 0.5% (w/v), for the above yeasts, respectively. The anti-yeast activities of DGC12 and SC16 were gradually increased with a decrease in pH, in a manner similar to that of SB, except for the action of SC16 on C. albicans, for which the activity was more effective at pHs 5.0 and 6.0 than at pHs 4.0 and 7.0. Among DGCs tested having different fatty acid moieties in the molecule, lauroyl ester (DGC12) was more effective than myristoyl and palmitoyl esters against S. cerevisiae and C. utilis. The inhibitory effect of DGC12 on the yeast growth depended upon both the cell density and the strength of aeration during the treatment. Further, DGC12 was found to kill S. cerevisiae and C. utilis cells at a rather low concentration of 0.005% (w/v) in 50mM acetate buffer at pH5.0, although, against C. albicans cells, only slight fungicidal activity was demonstrated at a high concentration of 0.5% (w/v). The results obtained support the effectiveness of practical application of DGC12 to acidic foods for the control of growth and survival of general yeasts such as S. cerevisiae and C. utilis.

Swallowing Function and Nutritional Status in Japanese Elderly People Receiving Home-care Services: A 1-year Longitudinal Study

OBJECTIVES

Malnutrition is a serious health concern for frail elderly people. Poor oral function leading to insufficient food intake can contribute to the development of malnutrition. In the present study, we explored the longitudinal association of malnutrition with oral function, including oral health status and swallowing function, in elderly people receiving home nursing care.

DESIGN

Prospective observational cohort study with 1-year follow-up.

SETTING

Two mid-sized cities in Fukuoka, Japan from November 2010 to March 2012.

PARTICIPANTS

One hundred and ninety-seven individuals, aged ≥ 60 years, living at home and receiving home-care services because of physical disabilities, without malnutrition.

MEASUREMENTS

Oral health status, swallowing function, taking modified-texture diets such as minced or pureed foods, nutritional status, cognitive function, and activities of daily living were assessed at baseline. The associations between malnutrition at 1-year follow-up and these related factors were analyzed using a logistic regression model.

RESULTS

Swallowing disorders [risk ratio (RR): 5.21, 95% confidence interval (95% CI): 1.65-16.43] were associated with malnutrition. On the other hand, oral health status did not have a direct association with malnutrition.

CONCLUSION

Swallowing disorders may be associated with the incidence of malnutrition in elderly people receiving home-care. The findings indicate that maintaining swallowing function may contribute to the prevention of malnutrition in frail elderly people.

Modifications of azoxymethane-induced carcinogenesis and 90-day oral toxicities of 2-tetradecylcyclobutanone as a radiolytic product of stearic acid in F344 rats

A 90-day oral toxicity test in rats was performed to evaluate the toxicity of 2-tetradecylcyclobutanone (2-tDCB), a unique radiolytic product of stearic acid. Six-week-old male and female F344 rats (n=15/group) were given 2-tDCB at concentrations of 0, 12, 60 and 300 ppm in a powder diet for 13 weeks. Slight dose-dependent increases in serum total protein and albumin in male rats were found, but these changes were not considered to be a toxic effect. The fasting, but not non-fasting, blood glucose levels of the male rats in the 300 ppm group and female rats in the 60 and 300 ppm groups were lower than those of the controls. Gas chromatography-mass spectrometry analysis showed dose-dependent accumulation of 2-tDCB in adipose tissue, notably in males. Next, we performed an azoxymethane (AOM)-induced two-stage carcinogenesis study. After injection of 6-week-old male F344 rats (n=30/group) once a week for 3 weeks, the animals received 2-tDCB at concentrations of 0, 10, 50 and 250 ppm in a powder diet for 25 weeks. The incidences of colon tumors for the 2-tDCB dosages were 34%, 45%, 40% and 37%, respectively, and were not statistically significant. These data suggest that 2-tDCB shows no toxic or tumor-modifying effects under the present conditions, and that the no-observed-adverse-effect level for 2-tDCB is 300 ppm in both sexes, equivalent to 15.5 mg/kg b.w./day in males and 16.5 mg/kg b.w./day in females.

Cancer whole-genome sequencing: present and future

Recent explosive advances in next-generation sequencing technology and computational approaches to massive data enable us to analyze a number of cancer genome profiles by whole-genome sequencing (WGS). To explore cancer genomic alterations and their diversity comprehensively, global and local cancer genome-sequencing projects, including ICGC and TCGA, have been analyzing many types of cancer genomes mainly by exome sequencing. However, there is limited information on somatic mutations in non-coding regions including untranslated regions, introns, regulatory elements and non-coding RNAs, and rearrangements, sometimes producing fusion genes, and pathogen detection in cancer genomes remain widely unexplored. WGS approaches can detect these unexplored mutations, as well as coding mutations and somatic copy number alterations, and help us to better understand the whole landscape of cancer genomes and elucidate functions of these unexplored genomic regions. Analysis of cancer genomes using the present WGS platforms is still primitive and there are substantial improvements to be made in sequencing technologies, informatics and computer resources. Taking account of the extreme diversity of cancer genomes and phenotype, it is also required to analyze much more WGS data and integrate these with multi-omics data, functional data and clinical-pathological data in a large number of sample sets to interpret them more fully and efficiently.

Important role of catalase in the cellular response of the budding yeast Saccharomyces cerevisiae exposed to ionizing radiation

Ionizing radiation indirectly causes oxidative stress in cells via reactive oxygen species (ROS), such as hydroxyl radicals (OH(-)) generated by the radiolysis of water. We investigated how the catalase function was affected by ionizing radiation and analyzed the phenotype of mutants with a disrupted catalase gene in Saccharomyces cerevisiae exposed to radiation. The wild-type yeast strain and isogenic mutants with disrupted catalase genes were exposed to various doses of (60)Co gamma-rays. There was no difference between the wild-type strain and the cta1 disruption mutant following exposure to gamma-ray irradiation. In contrast, there was a significant decrease in the ctt1 disruption mutant, suggesting that this strain exhibited decreased survival on gamma-ray exposure compared with other strains. In all three strains, stationary phase cells were more tolerant to the exposure of gamma-rays than exponential phase cells, whereas the catalase activity in the wild-type strain and cta1 disruption mutant was higher in the stationary phase than in the exponential phase. These data suggest a correlation between catalase activity and survival following gamma-ray exposure. However, this correlation was not clear in the ctt1 disruption mutant, suggesting that other factors are involved in the tolerance to ROS induced by irradiation.