High Water Activity Research Articles

Targeted Docking of Localized Hydrogen Bond for Efficient and Reversible Zinc-Ion Batteries.

Hydrogen bond (HB) chemistry, a pivotal feature of aqueous zinc-ion batteries, modulates electrochemical processes through weak electrostatic interactions among water molecules. However, significant challenges persist, including sluggish desolvation kinetics and inescapable parasitic reactions at the electrolyte-electrode interface, associated with high water activity and strong Zn2+-solvent coordination. Herein, a targeted localized HB docking mechanism is activated by the polyhydroxy hexitol-based electrolyte, optimizing Zn2+ solvation structures via dipole interaction and reconstructing interfacial HB networks through preferential parallel adsorption. By combining in situ spectroscopic characterizations with theoretical calculations, we elucidate the dynamic evolution of localized HB networks, which enhance Zn2+ deposition kinetics and homogeneity, suppress water-induced side reactions, and mitigate vanadium framework collapse. Our findings support that the targeted HB docking strategy facilitates fast interfacial ion transport kinetics and enables high reversibility, with a substantially prolonged symmetric cell lifespan exceeding 5000 h. This work markedly advances the efficient and reversible zinc-based batteries.

Targeted Docking of Localized Hydrogen Bond for Efficient and Reversible Zinc‐Ion Batteries

Hydrogen bond (HB) chemistry, a pivotal feature of aqueous zinc‐ion batteries, modulates electrochemical processes through weak electrostatic interactions among water molecules. However, significant challenges persist, including sluggish desolvation kinetics and inescapable parasitic reactions at the electrolyte‐electrode interface, associated with high water activity and strong Zn2+‐solvent coordination. Herein, a targeted localized HB docking mechanism is activated by the polyhydroxy hexitol‐based electrolyte, optimizing Zn2+ solvation structures via dipole interaction and reconstructing interfacial HB networks through preferential parallel adsorption. By combining in situ spectroscopic characterizations with theoretical calculations, we elucidate the dynamic evolution of localized HB networks, which enhance Zn2+ deposition kinetics and homogeneity, suppress water‐induced side reactions, and mitigate vanadium framework collapse. Our findings support that the targeted HB docking strategy facilitates fast interfacial ion transport kinetics and enables high reversibility, with a substantially prolonged symmetric cell lifespan exceeding 5000 h. This work markedly advances the efficient and reversible zinc‐based batteries.

Weak H-Bond Interface Environment for Stable Aqueous Zinc Batteries.

Hydrogen evolution reaction and Zn dendrite growth, originating from high water activity and the adverse competition between the electrochemical kinetics and mass transfer, are the main constraints for the commercial applications of the aqueous zinc-based batteries. Herein, a weak H-bond interface with a suspension electrolyte is developed by adding TiO2 nanoparticles into the electrolytes. Owing to the strong polarity of Ti-O bonds in TiO2, abundant hydroxyl functional groups are formed between the TiO2[110] active surface and aqueous environment, which can produce a weak H-bond interface by disrupting the initial H-bond networks between the water molecules, thereby accelerating the mass transfer of Zn2+ and reducing the water activity. In consequence, the Zn||Zn symmetrical cells display reversible Zn plating/stripping behaviors with a high Coulombic efficiency of 99.7% over 700 cycles. Moreover, the TiO2-based suspension strategy is also applicable to other zinc salt systems and exhibits fast plating/stripping behaviors. The suspension electrolyte enables long-term full cells, including Zn||PANI hybrid capacitors and Zn||ZnVO full batteries.

Occurrence of <i>Salmonella</i> and presumptive <i>Bacillus cereus</i> in sesame products from Swiss retail stores

Sesame products such as tahini (tahin) or halva (halwa or helva), originating from Arabic cuisine, are becoming increasingly popular in Switzerland. Pathogens, such as Salmonella, can contaminate sesame products, as evidenced by various product recalls. In this study, the occurrence of Salmonella and Bacillus cereus group members was investigated in 100 sesame products (25 sesame seeds, 16 halva, 19 different sesame pastes, 7 sesame bars, 25 hummus, and 8 other products containing sesame) collected from Swiss retail stores. None of the products were positive for Salmonella, whereas B. cereus group members could be detected with bacterial counts between 1×102 and 9×102 CFU/g in 11 out of 100 (11%) products. The 11 isolates identified by matrix-assisted laser desorption ionization-time of flight were whole-genome sequenced with Illumina technology to confirm the identity of the pathogen, determine its toxin gene profile, and perform panC typing. Most of the isolates harbored genes encoding the enterotoxins Nhe, Hbl, and CytK. The isolates were assigned to diverse B. cereus group members, including one identified as B. cytotoxicus. In addition, one of the isolates matched genetically with the Thurigiensis strain used in biopesticide products. In conclusion, none of the investigated sesame products contained significant levels of Salmonella or B. cereus group members. However, as B. cereus with pathogenic potential was detected in multiple samples, proper storage is crucial to prevent its growth and ensure consumer safety, especially for products with high water activity such as hummus.

Active Site Studies to Explain Kinetics of Lipases in Organic Solvents Using Molecular Dynamics Simulations.

This study investigates the intricate dynamics underlying lipase performance in organic solvents using comprehensive molecular dynamics (MD) simulations, supported by enzyme kinetics data. The study reveals that a single criterion can neither predict nor explain lipase activity in organic solvents, indicating the need for a comprehensive approach. Three lipases were included in this study: Candida antarctica lipase B (CALB), Rhizomucor miehei lipase (RML), and Thermomyces lanuginosus lipase (TLL). The lipases were investigated in acetonitrile, methyl tert-butyl ether, and hexane with increasing water activity. Computational investigations reveal that CALB's activity is negatively correlated to water cluster formations on its surface. In contrast, TLL's and RML's activity profiles show no negative effects of high water activity. However, TLL's and RML's activities are highly correlated to the conformation and stability of their active site regions. This study may pave the way for tailored applications of lipases, highlighting some of the factors that should be considered when lipase-catalyzed reactions are designed.

Chemical Characterization and Antioxidant Activity of Rosa canina L. From Çekerek Region of Yozgat, Turkey

Rosehip, renowned for its bioactive richness, including phenolic acids, flavonoids, carotenoids, and ascorbic acid, exhibits significant antioxidant and health-promoting potential. This study investigated the physicochemical, mineral, and phytochemical characteristics of rosehips sourced from the Çekerek region of Yozgat, Turkey, to evaluate their suitability as a functional food. The rosehips exhibited high dry matter content and low water activity, suggesting excellent stability for storage and processing. Furthermore, the rosehips contained substantial mineral content, including potassium, calcium, magnesium, iron, and zinc, which enhances their nutritional value. Phytochemical analysis revealed a significant phenolic content, potent antioxidant activity, and exceptional vitamin C levels, positioning Çekerek rosehips as a superior natural antioxidant source. These findings underscore the influence of Çekerek's unique environmental conditions on rosehip composition and highlight their potential applications in the functional food, nutraceutical, and pharmaceutical sectors, addressing the increasing demand for natural antioxidants. This research contributes to the understanding of regional variations in Rosa canina and provides a basis for further investigation into the bioavailability, clinical applications, and development of value-added products from Çekerek rosehips.

Impact of High Hydrostatic Pressure and UV-C Radiation on Total Aerobic Bacteria in Minas Frescal Cheese.

Minas Frescal cheese (MFC) is a perishable product with high water activity and neutral pH, conditions that favor the development of microorganisms. Total aerobic bacteria (TAB) can deteriorate the cheese, negatively affecting its sensory characteristics. By controlling TAB, the shelf life of the product is extended and its quality is maintained, contributing to meeting consumer expectations. This study aimed to evaluate the individual and combined effect of technological treatments of high hydrostatic pressure (HHP) and ultraviolet C radiation (UV-C) on the TAB count present in the natural microbiota of MFC, as an alternative to control the microbiological quality of this product. After production, MFC were subjected to treatments with different levels of HHP (100 to 400 MPa/10 min) and UV-C (0.097 to 0.392 J/cm2.s-1). The combinations of HHP and UV-C doses were determined by a central composite rotational design (CCRD). The model efficiently described the individual and combined effect of HHP and UV-C on TAB, demonstrating that gradually increasing HHP levels reduces TAB counts in MFC, regardless of the UV-C dose applied. This study contributes significantly to the literature by providing new insights into how these technologies can be used to improve the microbiological quality of fresh cheeses.

Gallium-Mediated switching in product selectivity for CO2 hydrogenation over Ni/CeO2 catalysts

Achieving high activity and selectivity for the reverse water–gas shift (RWGS) reaction at low-temperatures continues to pose a significant challenge. Ni-based catalysts have been widely employed in CO2 hydrogenation due to their strong capacity to dissociate H2, but it exhibits low selectivity for CO. Herein, we successfully altered the product selectivity for CO2 hydrogenation via controlling the distribution of Ga species on Ni/CeO2 catalysts. When Ga was combined with Ni to form the spinel of NiGa2O4 (NiGa2O4/CeO2), the main product selectivity was CO. While, the Ga was doped into CeO2 to support Ni (Ni/Ga4-CeO2), the product selectivity was the CH4. The NiGa2O4 spinel supported on CeO2 exhibits excellent performance in the RWGS reaction, with a CO selectivity over 99 %, and a production rate as high as 74.5 mmol/gcat·h at 450 °C and 24000 mL/gcat·h, without any loss of activity after 72 h. The Ni/Ga4-CeO2, containing metallic Ni species and abundant oxygen vacancies, enhances the methanation process, with a CO2 conversion as high as 81.38 %, and a CH4 production rate of 136 mmol/gcat·h. The CO-TPD analysis and density functional theory calculation reveals that the NiGa2O4/CeO2 catalyst exhibits weak adsorption of CO*, which plays a key role in enhancing the selectivity towards CO. Subsequent in-situ DRIFTS analysis further confirms that the differences in CO2 hydrogenation product obtained from NiGa4/CeO2 and Ni/Ga4-CeO2 can be attributed to the formation of different intermediate species over their surface, leading to a change in the selectivity of CO2 hydrogenation products. This study provides an insight to switch the product selectivity for CO2 reduction by controlling the distribution of Ga species.

Changes in the physicochemical properties of yellow pitahaya (Hylocereus megalanthus) during storage

Fresh fruits are essential for their flavor and nutritional value, and storage is one factor that decreases their shelf life. Low temperature or cold storage is a strategy to prolong the shelf life and maintain quality. Yellow pitahaya (Hylocereus megalanthus) was collected during the 2023 season, during May in the district of Magdalena (Chachapoyas, Amazonas, Peru). This study evaluated the physicochemical properties of yellow pitahaya stored at different conditions (room temperature, 2°C, and 4°C) every 15 days: Water activity, pH, total soluble solids (TSS), titratable acidity (TA), maturity index, antioxidant activity (by DPPH and ABTS) were also determined. The results showed significant changes in the physicochemical properties of pitahaya stored at different temperatures. The pitahaya stored at room temperature had higher water activity than samples stored at 2°C and 4°C, decreasing their solid content. The color of pitahaya also varied with the storage temperature, being 2°C ideal for maintaining the color. Therefore, storage at low temperatures slows down the degradation of the fruit, although precautions should be taken due to its susceptibility to physiological changes. Proper storage of pitahaya is essential to maintain its freshness and nutritional value.

Characterization of Chayotextle Starch Films Supplemented with Essential Oils and Their Effect as a Coating on the Shelf Life of Bread

AbstractStarch extracted from chayote root is a carbohydrate polymer ideal for producing edible films, especially when combined with essential oils. This study develops starch‐based edible films incorporating rosemary (E‐RO) or cinnamon (E‐CO) essential oil and assesses their effectiveness in extending bread's shelf life. Films with essential oils exhibit significantly higher (p < 0.05) water vapor permeability compared to control films without oil. Tensile strength and elongation tests show that films stored at low water activity (aw < 0.443) have greater strength and lower elongation (p < 0.05) than those stored at high water activity. Additionally, essential oils significantly enhance the films' antimicrobial and antifungal activity against selected microorganisms. Edible films with essential oils are fully degraded around day 18, while control films degraded by day 15. Bread coated with these films is stored at different temperatures to analyze effects on physicochemical properties and hardness. Sensory analyses reveal that coated bread receives overall acceptance scores (7.61–8.64) similar to control bread and show delayed mould growth during the 15‐day storage period. These findings suggest that chayote root starch‐based films with essential oils have strong potential as active food coatings, effectively extending the shelf life of stored bread.

Influence Marination Length Using Evaporated Roselle (Hibiscus sabdariffa Linn) Extract on Microbiological Quality of Beef Se'i

Experiment was conducted to determine the influence of marination length using evaporated roselle extract (Hibiscus sabdariffa Linn) on microbiological aspects of beef se’i. The completly randomized design (CRD) with 4 treatments 4 replicates was applied in this experiment. Those treatments were P0 marination length of 12 hours without roselle extract; P1 marination length 6 hours with 5% roselle extract; P2 marination length 12 hours with 5% roselle extract, and P3 marination length 18 hours with 5% roselle extract. The parameters measured were pH, moisture, water activity and total plate count. Data compilled were analyzed using variance analysis and Duncan’s multiple range test. The result of analysis showed that pH and moisture of beef se’i significantly affected by marination length using evaporated roselle extract (P<0.05) but no significant (P>0.05) on water activity and total plate count. It was concluded that beef se’i produced through the marination process with different lengths of time (6, 12 and 18 hours) using evaporated rosela extract, showed characteristics of decreased pH, increased water content with high water activity and total plate count tended to decrease. The best marination length of this study was 12 hours using rosela extract.

Heat and mass transfer and deformation during chiffon cake baking

The structural transformation from a foam liquid to a porous solid during cake baking involves pore development and solidification, resulting in complex coupled heat transfer, mass transfer, and deformation processes. Studying the mechanisms can provide important references for understanding the physical processes of numerous foods containing gas pores. We constructed a multiphase flow-deformation model for chiffon cake baking, and validated its accuracy by comparing the experimental results of temperature and height. Based on the model, the heat transfer, mass transfer, and deformation characteristics were investigated. In the pore-closed region, the evaporation-diffusion-condensation process of water vapor enhances heat transfer, and its contribution to heat transfer has an equivalent thermal conductivity of up to 0.64 W/(m·K), which increases the heating rate. In the pore-opening region, the water vapor evaporates from the high-temperature, high-water activity region and is transported towards the lower-temperature region and external environment. This process enhances heat transfer and induces an evaporative cooling effect, resulting in a uniform temperature distribution that remains below 100 °C across the majority of the region. Cake expansion occurs in the low-viscosity, pore-closed region, and the water vapor generated at high temperatures serves as the primary driving force source, contributing up to 84.6%.

Long-duration aqueous Zn-ion batteries achieved by dual-salt highly-concentrated electrolyte with low water activity

Aqueous Zn-ion batteries have attracted much attention due to their unique high safety and low-cost merits. However, their practical applications are at a slow pace due to their short cycle life, which fundamentally results from the instability of the positive/negative electrode interface in the traditional dilute aqueous electrolytes with high water activity. Developing highly concentrated electrolyte (HCE) has been considered as an effective solution. Unlike previous studies of single salt-based HCE (SS-HCE), herein, a new dual-salt HCE (15 m ZnCl2 + 10 m NH4NH2SO3 DS-HCE) was proposed for the first time. DS-HCE was proven to simultaneously possess higher conductivity than traditional dilute electrolytes and ultralow water activity of SS-HCE by the regulation of dual high-concentration salts on the solvation structure, which renders the Zn||Zn symmetric cell the record-long cycling life of 2200 h compared with those with SS-HCE (30 m ZnCl2, 300 h) and other reported HCEs. Additionally, the Zn||NH4V4O10 full cell with DS-HCE demonstrated impressed rate capability within a wide-range current densities from 0.1 to 10 A g−1. Moreover, at the high current density of 5 A g−1, the full cell shows almost 100% capacity retention after 4000 cycles, which indicates the promising future of the DS-HCE system for long-duration aqueous Zn-ion batteries.

Heterogeneous water distribution in between peridotite xenoliths from Kaapvaal Craton kimberlites: Constraints on diamond barren nature of kimberlites

Nominally anhydrous mantle minerals (olivine, pyroxenes, garnets, etc.) in 11 peridotite xenoliths from four different uneconomic and economic Kaapvaal Craton kimberlite pipes (Matsoku, Thaba Putsoa, Pipe 200 and Bultfontein) have been investigated using Fourier transform infrared spectroscopy (FTIR). All xenoliths contain accessories of garnet, diopside, chromite, and phlogopite. High orthopyroxene content (>30 mol vol.%) in most xenoliths from all kimberlites and its interconnected channel-like nature hint towards hydrous siliceous fluid metasomatism. Peridotite xenoliths from uneconomic kimberlites show development of phlogopite and clinopyroxene (± chromite) forming veins and in garnet rims suggesting metasomatism by alkaline silico-carbonatite (possibly kimberlite-related) melt. The xenoliths contain significant H2O in olivine (17–62 ppm), orthopyroxene (21–230 ppm), and clinopyroxene (87–833 ppm), whereas garnets are dry and only show IR absorbance bands at > 3,670 cm−1 for contamination of hydrous minerals. Compared to the economic kimberlites in the Kaapvaal Craton, the uneconomic kimberlite xenoliths from this study have lower orthopyroxene and olivine H2O content. In the xenoliths affected by garnet breakdown metasomatism, the H2O content of orthopyroxene and olivine is higher and lower, respectively. The structural hydroxyl distribution profile across olivine and higher inter-mineral water partition coefficient, suggest diffusion of hydrogen and possible re-equilibration. Statistical analysis of the olivine spectra suggests that hydrogen bands at 3540, 3624, 3638, and 3672 cm−1 are a good discriminant of economic and uneconomic kimberlites and in literature, they are associated with metasomatism, weathering-associated processes, high water activity, and oxygen fugacity. The lower water concentration in xenoliths from uneconomic kimberlite from the margin of the craton than the economic kimberlites from the interior of the Kaapvaal Craton and identified metasomatism hints towards dehydration of xenoliths by water-poor and CO2-rich melts in tectonized cross-lithospheric zones causing diamond resorption and may be responsible for the diamond-poor nature of uneconomic kimberlites in northern Lesotho.

Viability of 3D printing of andean tubers and tuberous root puree

Three-dimensional (3D) printing is revolutionizing the industry. This technology can potentially transform and improve challenges in the food industry. This study evaluated the viability of 3D printing of puree made from camote and mashua flours. Before drying and grinding, the roots were pretreated with cooking and microwaving. First, the microstructure of the flours was evaluated using A Scanning Electron Microscope (SEM). The physicochemical, rheological, and extrusion properties of the purees were assessed. Furthermore, image analysis was conducted to observe the effect of time on 3D-printed figures. Four formulations were evaluated: Camote cooked (CamC), Camote microwaved (CamM), Mashua cooked (MasC), and Mashua microwaved (MasM), all containing a percentage of whole milk. SEM results revealed that heat treatments influence grain shape in mashua, leading to round or oval grains; this behavior was not observed in camote treated by microwave. X-ray diffraction (XRD) analysis shows that microwaved camote granules retain their crystalline structure and shape. High water activity values were observed in camote samples; these results could be due to starch and sugar content. Color analysis revealed differences between samples less appreciable by the human eye in mashua. Rheological analysis indicated a solid behavior, with both G∗ and G′ values similar to or higher than G″ and significant differences among all samples. The tangent values were <1, indicating elastic properties dominated in all samples. Cooked samples showed better proportion fidelity than microwaved ones due to the retrogradation process. The study suggests camote and mashua flours pretreated by cooking present better printability than microwaving. This effect can be related to the higher starch denaturation.

Effects of temperature and storage duration on quality of an insect artificial diet.

Artificial diets are widely used to produce insects for research and education programs. Completed diets, in which the diets are fully made from individual ingredients and ready to use, often have high water activity, making them vulnerable to degradation. Proper storage is critical to maintaining diet quality, yet the storage conditions are not well investigated. In this study, we characterized the effects of storage conditions (temperatures and storage duration) on the quality of a diet capable of rearing both specialist and generalist insect species. The completed diet, produced by both private industry and a USDA-Agricultural Research Service laboratory, was exposed to varying temperatures during a 24-hour transit over 1600km. After transit, it was stored at 4°C for a total storage period of 28 days. In a separate experiment, the completed diet was stored immediately after diet production at five fixed temperatures (-20, 4, 22, 25, and 33°C) for up to 28 days. For both experiments, at 5 intervals after storage (1, 7, 14, 21, and 28 days), diet quality was accessed by life history parameters (survival, molting, and weight) of western corn rootworm (Diabrotica virgifera virgifera LeConte) larvae, the most serious maize pest in the United States. Our results showed that exposure to varying temperatures between -2°C and 27°C for 24 hours had no significant impact on diet quality. However, extended storage (beyond 24 hours) at any of the fixed temperatures negatively affected diet quality. Insects reared on diets stored for over 24 hours at fixed temperatures ranging from -20°C to 33°C had significant declines in performance. Among the tested temperatures, -20°C and 4°C were found to be the most effective for preserving diet quality. At these low temperatures, there were no significant changes in insect weight and survival for diets stored within 21 and 28 days, respectively, though molting was significantly reduced within 7 days of storage. These findings provide the base of information on the storage conditions for completed diets, supporting the production of healthy insects.

Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent

A rare porphyritic charnockite that is girdled by and mineralogically grades to biotite granite occurs as a part of the Chotanagpur Granite Gneissic Complex (CGGC) in and around Massanjore, Jharkhand, India. Preservation of certain textural features, including (a) euhedral to subhedral grains of orthopyroxene, (b) low dihedral angle subtended by orthopyroxene and plagioclase grains, and (c) relict intergranular and porphyritic textures, are consistent with the view that orthopyroxene in the studied rocks has a magmatic origin. Preserved magmatic features and other petrological attributes of these rocks do not support any significant mass change beyond a few tens of microns during the overprinting high-grade metamorphism. The geochemical variation of the felsic rock suite (porphyritic charnockite and biotite granite) indicates that they are cogenetic and are derived from a ferroan A-type granitoid magma by crystal fractionation. The observed geochemical trend of the studied felsic rock suites has been simulated by phase equilibria modelling in the open system using the system components Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2. The observed mineralogical and geochemical attributes and the results of the modelling study are consistent with a petrogenetic process in which high magma temperature (> 900 °C), low pressure, and low water activity in the parental melt favoured the separation of an orthopyroxene bearing cumulate assemblage (orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + magnetite) in the initial part of the magmatic differentiation. Removal of this anhydrous cumulitic assemblage raised the bulk H2O content in the residual melt. Orthopyroxene became unstable with respect to biotite in the evolved melt that eventually crystallised minerals that formed the biotite granite. An increase in magma fO2 also restricts the orthopyroxene stability in felsic magma. Taken together all the petrological and geochemical attributes, we demonstrate that fractionation of an orthopyroxene-bearing crystal cumulate from the melt is essential to form the charnockites, and that the biotite granite forms from the evolved melt after the fractionation. The charnockite-biotite granite association of the studied area was formed in an extensional tectonic setting, presumably during the breakdown of the Columbia Supercontinent.

Fermented fruits and legumes in Africa: production factors and health benefits

SummaryFermentation is an age‐long food processing tool used to preserve and develop functional foods and beverages. Fruits in particular have a very short shelf life due to their high water activity, favourable to microbial decomposition and spoilage, while legumes are protein‐rich crops that require improved protein digestibility. These are some standout reasons for applying this tool to develop fermented fruit‐ and legume‐based products. From multifarious fruit‐based beers, non‐alcoholic beverages and alcoholic drinks to legume‐based condiments and meals, fermentation has been used over time in Africa to enhance the food security, safety, nutrition, healthfulness and livelihoods of the people. As the nutrition and economic prospects of African fermented fruit‐ and legume‐based products are huge not only to the African continent but globally (as African diasporans and their interracial friends, spouses and relatives are notably consuming them), they are fraught with opportunities and challenges. This review describes the production factors (including raw material selection, processing techniques, environmental conditions and the role of microorganisms) and health benefits of these African fermented products. Safety concerns, fermentation challenges and other considerations are also discussed. Further studies targeting fermentation and production of novel, healthy and safer fruit‐ and legume‐based African food products are warranted due to their potential positive contribution to African and global hunger and malnutrition issues.

Role of water activity on sporulation traits and resistance to 915 MHz microwave in the emetic type of Bacillus cereus on rice

The objective of this study is to investigate the influence of water activity on the sporulation of emetic strains of Bacillus cereus and the subsequent susceptibility of sporulated B. cereus to 915 MHz microwave treatment. Water activity levels were manipulated in the sporulation medium by adjusting glycerol concentrations to 0 %, 3 %, 7.5 %, and 10 %, resulting in corresponding water activities of 0.996, 0.981, 0.971, and 0.960, respectively and sporulated at 30℃. These changes in water activity were intended to simulate the variations in water activity that can occur during the cultivation and processing of rice, where B. cereus is commonly found. Sporulation rates increased with higher water activity, achieving over 90 % of total cells after 3, 5, 5, and 6 days of incubation at water activities of 0.996, 0.981, 0.971, and 0.960, respectively. Resistance to microwave treatment increased with higher water activity levels during sporulation. Microwave treatment for 5 min yielded a reduction of 3.03 log CFU/g at a water activity of 0.960 and 1.98 log CFU/g at 0.996 during sporulation. Lower water activity led to higher % dipicolinic acid (DPA) release during microwave treatment, as measured using a spectrometer, indicating greater membrane damage. To investigate the morphology of spores, transmission electron microscopy was used. Spores produced at lower water activity levels were observed to be enveloped by the mother cell, whereas those sporulated at higher water activity levels were distinct from the mother cell. Additionally, spores sporulated at higher water activity levels exhibited higher wet density in Percoll gradient. The levels of germination were also compared after sporulation under different water activity medium using L-alanine. The spores evolved under low water activity exhibited higher germination level compared to those from high water activity conditions. These findings suggested that water activity conditions during sporulation induce variations in morphology, density, germination level, and resistance to 915 MHz microwave. Our experimental results indicated that, even with the same sporulation percentage, there can be differences in the maturation stage, indicating that the level of 915 MHz microwave treatment should be adjusted according to the sporulation conditions of B. cereus.

Sea spray allows for the growth of subaerial microbialites at the driest desert on Earth

Due to its extreme conditions, microbial life in the Atacama Desert is known to survive in well-protected micro-habitats (hypolithic, endolithic, etc.), but rarely directly exposed to the environment, that is, epilithic habitats. Here we report a unique site, La Portada, a cliff confronting the Pacific Ocean in the Coastal Range of this desert, in which the constant input of water provided by the sea spray allows for the growth of a black-colored epilithic subaerial microbial ecosystem. Formed by a complex community of halophilic microorganisms belonging to the three domains of life, this ecosystem displays the typical three-dimensional structure of benthic microbialites, coherent with the presence of a diversity of cyanobacteria (including species from the genera that are known to form them), a constant high water activity and an ample availability of carbonate ions. From these microbialites we isolated Hortae werneckii, a fungal species which by producing melanin, not only explains the dark color of these microbialites, but may also play the role of protecting the whole community from extreme UV radiation. A number of biosignatures not only confirmed sea spray as the main source of water, but also suggests that one place to consider for the search of evidences of life on Mars would be on the paleo-coastlines that surrounded vanished oceans such as that on Aeolis Dorsa.