Search Results (268)

To study the effect of cold plasma (CP) on the refrigerator shelf life of coconut water, microorganism growth and diversity and physicochemical properties were investigated. Results indicated that CP treatment did not cause significant color changes in coconut water, with turbidity remaining lower than the control even after 6 days of storage. Enzymatic activity analysis revealed reduced polyphenol oxidase (PPO) and peroxidase (POD) levels in treated samples. Specifically, the 12 s CP treatment resulted in the lowest antioxidant capacity values: 15.77 Fe²⁺/g for ferric reducing antioxidant power (FRAP), 37.15% for DPPH radical scavenging, and 39.51% for ABTS⁺ radical scavenging. Microbial enumeration showed that extended CP treatment effectively inhibited the growth of total viable counts, psychrophilic bacteria, lactic acid bacteria, and yeast. High-throughput sequencing identified Leuconostoc, Carnobacterium, and Lactobacillus as the dominant bacterial genera. During storage, Carnobacterium was the primary genus in the early stage, while Leuconostoc emerged as the dominant genus by the end of the storage period. In summary, CP as an effective non-thermal technology was able to maintain quality and antioxidant capacity, inhibit microbial growth, and delay the spoilage in coconut water to help extend the refrigerated shelf life of the product. Full article

Cold environments challenge the structural and functional integrity of membrane proteins, requiring specialized adaptations to maintain activity under low thermal energy. Here, we investigate the molecular basis of cold tolerance in the peptide transporter PepT1 from the Antarctic icefish (Chionodraco hamatus, ChPepT1) using molecular dynamics simulations, binding free energy calculations (MM/GBSA), and dynamic network analysis. We compare ChPepT1 to its human ortholog (hPepT1), a non-cold-adapted variant, to reveal key features enabling psychrophilic function. Our simulations show that ChPepT1 displays enhanced global flexibility, particularly in domains adjacent to the substrate-binding site and the C-terminal domain (CTD). While hPepT1 loses substrate binding affinity as temperature increases, ChPepT1 maintains stable peptide interactions across a broad thermal range. This thermodynamic buffering results from temperature-sensitive rearrangement of hydrogen bond networks and more dynamic lipid interactions. Importantly, we identify a temperature-responsive segment (TRS, residues 660–670) within the proximal CTD that undergoes an α-helix to coil transition, modulating long-range coupling with transmembrane helices. Dynamic cross-correlation analyses further suggest that ChPepT1, unlike hPepT1, reorganizes its interdomain communication in response to temperature shifts. Our findings suggest that cold tolerance in ChPepT1 arises from a combination of structural flexibility, resilient substrate binding, and temperature-sensitive interdomain dynamics. These results provide new mechanistic insight into thermal adaptation in membrane transporters and offer a framework for engineering proteins with enhanced functionality in extreme environments. Full article

Small heat shock proteins (sHsps) are ubiquitous low-molecular-weight chaperones that prevent protein aggregation under cellular stress conditions. In the absence of stress, they assemble into large oligomers. In response to stress, such as elevated temperatures, they undergo conformational changes that expose hydrophobic surfaces, allowing them to interact with denatured proteins. At heat shock temperatures in bacteria, large sHsp oligomers disassemble into smaller oligomeric forms. Methanogens are a diverse group of microorganisms, ranging from thermophilic to psychrophilic and halophilic species. Accordingly, their sHsps exhibit markedly different temperature dependencies based on their optimal growth temperatures. In this study, we characterized sHsps from both hyperthermophilic and mesophilic methanogens to investigate the mechanisms underlying their temperature-dependent behavior. Using analytical ultracentrifugation, we observed the dissociation of sHsps from a mesophilic methanogen into dimers. The dissociation equilibrium of these oligomers was found to be dependent not only on temperature but also on protein concentration. Furthermore, by generating various mutants, we identified the specific amino acid residues responsible for the temperature dependency observed. The C-terminal region containing the IXI/V motif and the α-crystallin domain were found to be the primary determinants of oligomer stability and its temperature dependence. Full article

This article explores how the location of a building in an urban area, the level of external air pollution, and the way a residence is used can affect indoor air quality. To assess this, this study used measurements of physical and chemical pollutants, as well as microbiological measurements, including counts of various bacteria and microscopic fungi. These included counts of mesophilic and psychrophilic bacteria, mannitol-positive and mannitol-negative Staphylococcus, Actinobacteria, Pseudomonas fluorescens, and microscopic fungi. The research involved analysing indoor and outdoor air quality in 38 selected spaces within buildings in the city of Poznań during the heating season. The study found that the eastern part of the city showed the highest levels of fungal contamination in the external environment. Furthermore, distinct differences were observed between the presence of microorganisms indoors and outdoors based on the results of bacterial and fungal aerosol studies. The authors advocate for including microbiological studies as part of standard air quality assessment indicators to reveal the extent and source of contamination, as similar issues may be present in cities around the world. Full article

Antarctica, with its harsh environmental conditions, is home to a wide variety of microorganisms, including filamentous fungi. The survival of Antarctic mycoflora has led to increasing interest in their adaptation. Extreme low temperatures, low water availability, frequent freeze–thaw cycles, strong winds, ultraviolet radiation, etc., are all prerequisites for accelerated production of reactive oxygen species (ROS) and the occurrence of oxidative stress (OS). Antarctic fungi have effective mechanisms to cope with the damaging effects of ROS. While the distribution, morphology, physiology, and biotechnological potential of these fungi are well documented, the role of oxidative stress in their adaptation is poorly understood. This has been one of the main research topics of our team for a long time, and a number of papers on our results have been published. This review summarizes the existing literature on the induction of oxidative stress in Antarctic psychrophilic, psychrotolerant, and mesophilic fungi by extreme conditions. The most recent and relevant studies reporting on the relationship between cold stress and OS biomarkers and the damaging effects of ROS on key intracellular biomolecules are presented. The contribution of both enzymatic and non-enzymatic antioxidant defenses to the fungal cell response is discussed. Full article

The psychrophilic aerobic heterotrophic bacterium, strain 1639^T, was isolated from the low-temperature Lake Untersee in Antarctica. The bacterium was Gram-positive, non-motile, yellow–green-pigmented, non-spore-forming, and a pleomorphic rod. Growth was observed at temperatures of 0–25 °C with an optimum at 10 °C. The strain used urea as a nitrogen source. The major fatty acids were i-C_16:0 (49.69%), ai-C_15:0 (17.59%), and C_16:1 branched (12.03%). Identified polar lipids were phosphatidylglycerols and a glycolipid. The respiratory quinone was determined to be MK-10. The genomic DNA G+C content was 68.03 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 1639^T was a member of the genus Cryobacterium, with the highest sequence similarity to C. arcticum SK1^T (98.4%), C. soli GCJ02^T (98.4%), C. lactosi Sr59^T (98.3%), C. zongtaii TMN-42^T (98.2%), and C. adonitolivorans RHLS22-1^T (98.1%). The ANI and the DNA–DNA hybridization estimate values between strain 1639^T and all type strains of species of the genus Cryobacterium were in the range of 84.3–87.8% and 20.5–40.3%, respectively. The combined genotypic and phenotypic data indicate that strain 1639^T represents a novel species within the genus Cryobacterium, for which the name Cryobacterium inferilacus sp. nov. is proposed with the type strain 1639^T (=KCTC 59142^T, =VKM Ac-2907^T, UQM 41460^T). Full article

In this study, an extract of white grape marc (GME), a by-product obtained during the winemaking process, was applied to the surface of gilthead seabream (Sparus aurata) fillets, which were then stored under refrigeration (4 °C) for a period of 14 days. The effects of GME were compared with those of ascorbic acid (one of the few additives authorized for fresh fish in the EU) and distilled water (as a control batch). Samples were taken at 1, 2, 4, 7, 9, 11, and 14 days postmortem (dpm) cold storage, and several objective quality parameters were measured (instrumental color, pH, water holding capacity, texture profile analysis—TPA, lipid oxidation, and microbial spoilage). The results showed that the grape extract significantly improved several of the parameters studied, not only compared to the control batch, but even compared to the ascorbic acid batch. Thus, GME slowed down the proliferation of psychrophilic bacteria, prevented the oxidation of muscle lipids, and even improved the firmness of the fillets compared to the other two experimental groups. On the other hand, minor effects on color, pH, or water retention capacity were observed. In the context of the scarcity of approved food additives for fresh fish in the EU and the strong consumer rejection of synthetic substances for this purpose, this grape extract could well represent a viable alternative. In addition to its natural origin, the use of GME as a food additive could also contribute to the valorization of winery by-products as part of a circular bioeconomy strategy. Full article

The influence of high-pressure processing (HPP) at 200, 400, and 600 MPa on spoilage bacterial diversity, microbial load, and chemical and sensory properties of the precooked edible portion of baby clam (PC-EP) was investigated. HPP at 400 MPa for 4 min (400 MPa) significantly prolonged shelf life and sensory acceptability up to 12 days, maintaining a total viable count (TVC) below 6 log CFU/g. In contrast, the TVC of both the control (without HPP treatment) and 200 MPa-treated samples exceeded this limit by day 0 and 3, respectively. The 400 MPa-treated samples showed a reduced load of psychrophilic bacteria, Aeromonas species, and lactic acid bacteria over 12 days. Additionally, coincidentally lower total volatile base and trimethylamine levels confirmed the good quality of HPP-treated PC-EP. Based on next-generation sequencing, a significantly lower microbial diversity index was found in the 400 MPa-treated samples, and it was dominated by Carnobacterium, Lactococcus, and Psychrobacter on day 12. In contrast, the control harbored spoilage bacteria, including Lactococcus, Aeromonas, Shewanella, and Pseudomonas, which correlated with higher acetic acid and acetoin levels as confirmed by HS-SPME-GC-EI/MS. These findings demonstrated that HPP at 400 MPa for 4 min was an effective non-thermal preservation method, extending the shelf life of PC-EP by inhibiting spoilage bacteria. Full article

This study examines the impact of added elderberry (EDB) extract on the physico-chemical, microbiological, and sensory properties of yogurt over a 21-day storage period. Two separate experiments were conducted: the first focused on testing concentrations of 0.05%, 0.1%, 0.2%, and 0.5% (w/w) EDB extract for impoving antioxidant properties and replacing potassium sorbate, a chemical preservative commonly used in dairy products, while the second aimed to enhance the bioactive compounds’ concentration by adding 0.5% EDB extract, and to assess the effect of a sweetener (agave syrup) on the sensory profile. Both experimental approaches demonstrated a significant increase (p < 0.01) in total phenolic content. In the first experiment, there was approximately 2.6 times more total phenolic content compared to the control (with a maximum of 11.71 mg GAE/100 g for the sample with 0.2% EDB extract), and about 6 times more with the addition of 0.5% EDB extract and agave syrup (with a maximum of 25.29 mg GAE/100 g). Additionally, the IC₅₀ value decreased for all samples with EDB extract, suggesting enhanced antioxidant activity. Specifically, the antioxidant activity was approximately 3.3 times higher for the control for samples obtained from homemade yogurt with EDB extract, and about 8 times higher for samples obtained by adding EDB extract to commercial yogurt, compared to their respective controls. The high stability of bioactive compounds during the storage period highlights the potential of EDB extract as a functional antioxidant ingredient. Microbiological analysis confirmed the safety of the yogurt, with lactic acid and mesophilic bacteria showing stable counts and minimal declines over time. In the first experiment, a reduction of about 2.3 CFU/g was observed from day 0 to day 21 in samples with 0.1% and 0.2% EDB extract, while the control sample showed a reduction of 1.84 CFU/g. However, the control sample recorded the growth of psychrophilic bacteria, yeasts, and molds. In the second experiment, the samples with 0.5% EDB extract showed an average reduction of approximately 0.35 CFU/g, while the control showed a reduction of 0.51 CFU/g, maintaining stable counts and no detectable growth of psychrophilic bacteria, yeasts, molds, or coliforms. Additionally, the inclusion of different concentrations of EDB extract, along with the combination of a higher concentration of EDB extract and agave syrup, improved the yogurt’s sensory attributes, thereby enhancing consumer acceptance. For the first experiment, 68% of the panelists expressed their preference for the samples with EDB extract, and 10% preferred the control sample. In the second experiment, 49% preferred the sample with 0.5% EDB extract and agave syrup, while 23% preferred the control sample. These findings support the integration of EDB extract into yogurt formulations to boost antioxidant properties while preserving microbiological stability. Future research should explore the potential health benefits and long-term effects of these functional dairy products. Full article

The present study evaluated the effect of ice storage on the freshness and quality of bullfrog (Lithobates catesbeianus) leg muscle. Biochemical, chemical, physical, and microbiological changes during 24 days of storage were analyzed. A rapid degradation of ATP into its intermediates (AMP, IMP, inosine, and hypoxanthine) was observed, with a significant increase in K-index (6.78% to 79.33%) and hypoxanthine concentration (3.93 ± 0.87 µmol/g), indicating a progressive reduction in freshness. The pH initially decreased due to post-mortem glycolysis but subsequently increased due to microbial activity and protein degradation. Volatile basic nitrogen (TVB-N) content increased significantly, reaching 27.36 mg/100 g, reflecting protein breakdown. A loss of texture was recorded, with a reduction in muscle firmness from 21.93 ± 1.36 Nw to 10.87 ± 1.08 Nw. Microbiological analyses showed an increase in bacterial load, with mesophiles and psychrophiles reaching 6.75 and 6.45 log CFU/g, respectively. These results indicate that the freshness and quality of bullfrog leg under ice storage remain within acceptable limits until day 18, but its quality and freshness decrease significantly toward the end of the study period. Full article

Cold-active enzymes hold promise for energy-efficient processes. Amylases are widely used in household and industrial applications, but only a few are cold-active. Here we describe three novel secreted amylases, Rho13, Ika2 and I3C6, all from bacteria growing in the cold and alkaline ikaite columns in Greenland. They all hydrolyzed starch to smaller malto-oligomers, but only Rho13 and Ika2 hydrolyzed cyclodextrins, and only Ika2 displayed transglycosylation activity. Ika2 forms a stable dimer, while both Rho13 and I3C6 are mainly monomeric. They all have optimal active temperatures around 30–35 °C and significant enzymatic activity below 20 °C, but Rho13 and I3C6 had an alkaline optimal pH, while Ika2 was markedly acidophilic. They showed complex dependence on Ca²⁺ concentration, with the activity of Rho13 and I3C6 following a bell-shaped curve and Ika2 being unaffected; however, removal of Ca²⁺ reduced the stability of all three enzymes. Loss of structure occurred well above the temperature of optimal activity, showing the characteristic psychrophilic divorce between activity and stability. MD simulations showed that Ika2 did not have a well-defined Ca²⁺ binding site, while Rho13 and I3C6 both maintained one stably bound Ca²⁺ ion. We identified psychrophilic features as higher levels of backbone fluctuations compared to mesophilic counterparts, based on a lower number of internal hydrogen bonds and salt bridges. This increased fluctuation was also found in regions outside the active site and may provide easier substrate access and accommodation, as well as faster barrier transitions. Our work sheds further light on the many ways in which psychrophilic enzymes adapt to increased catalysis at lower temperatures. Full article

Exopolysaccharides (EPSs) represent versatile biopolymers finding diverse applications in food, pharmaceuticals, and bioremediation industries. Extremophiles, thriving under extreme environmental conditions, have emerged as a promising source of novel EPSs with better stability and bioactivity. The present work reviews the complex influence of various abiotic factors and bioprocess parameters such as temperature, pH, carbon and nitrogen sources, C/N ratios, and oxygen transfer dynamics on the production of EPSs from extremophilic microorganisms. Results underline the important role of temperature for structural and functional properties of EPSs, from the synthesis of cryoprotective polymers in psychrophiles to the production of thermostable EPSs in thermophiles under cold stress. The pH has an extensive effect on enzymatic activities: optimal neutral to slightly acidic conditions exist for most strains. Carbon sources determine not only the yield of EPSs but also its structural features, while nitrogen sources and C/N ratios regulate the balance between biomass production and polymer biosynthesis. Besides that, oxygen transfer limitations—which may happen in particularly viscous or saline media—are overtaken by optimized bioreactor configuration and stirring strategies. These findings are highly relevant to the development of tailored cultivation conditions enabling the maximization of EPS yields and adaptation of its properties to comply with industrial requirements. This study provides a framework for enhancing EPS production by leveraging the adaptive traits of extremophiles. This approach supports the sustainable use of biopolymers, advances fermentation production processes, and helps uncover the underlying mechanisms involved. Full article

Pumpkin (P) production in Santiago del Estero, Argentina, is of high quality. The product is sold whole and fresh, and is traditionally consumed after being cooked in water. Due to its pleasant flavor (semi-sweet), it is widely accepted among consumers, being a potentially versatile product to be consumed fresh or minimally processed (MP). Processing increases food’s susceptibility to microbial spoilage, making it necessary to use sanitizers. In this work, the effect of different application methodologies at different concentrations of rosemary essential oil (REO) on the sensory characteristics and microbiological quality of grated P was evaluated. The product was washed, sanitized, cut, peeled, grated and centrifuged, and then REO was superficially incorporated in two concentrations (4 and 8 μL/mL), applied in three ways: sprayed (TA), immersion (TI) and by strips embedded in EO being adhered to the storage container (TV). The product was subsequently stored at 5 °C in sealed polypropylene bags of 35 μm. In addition, an immersion treatment with NaClO-100 ppm-3 min and a control without any additive were included. Samples were taken at 24 h and 8 days of storage, evaluating mesophilic aerobic microorganisms (MA), psychrophilic (Psy), enterobacteria (E) and mold and yeasts (MY). Sensory evaluation was carried out by trained judges, determining that aroma and flavor were the critical attributes for acceptability. At the end of storage, microbiological analysis showed that REO treatments presented levels of 10⁷ CFU/g, similar to NaCLO treatment, except TI with both concentrations, which was more effective in inhibiting the development of Psy and MY. Regarding aroma evaluation, at 8 days all treatments were acceptable, with the exception of TI and TV (8 μL/mL), while for flavor all treatments were acceptable with the exception of TI for both concentrations. Therefore, the application of TA and TV treatments at the lowest concentration could be considered for further studies to increase the shelf life of MP P. Full article

Background: Psychrobacter species are aerobic, Gram-negative, spherical-to-rod-shaped, psychrophilic bacteria that belong to the Moraxellaceae family. In spite of their uncommon manifestation in the general population, infections due to Psychrobacter spp. are increasingly identified especially in immunocompromised individuals or patients with severe comorbidities. Objectives: This review aims to analyze all reported instances of Psychrobacter spp. infections in humans, with an emphasis on data pertaining to epidemiology, microbiology, antimicrobial resistance, treatment strategies, and mortality outcomes. Methods: A narrative review was performed through a literature search of PubMed/MedLine and Scopus databases. Results: In total, 12 articles offered data on 12 patients infected with Psychrobacter spp. Their mean age was 33.41 years, while 63.64% of them were male. Immunosuppression was the predominant risk factor (33.3%). Bacteremia was the most commonly observed type of infection (41.6%), followed by meningitis, skin infection, and conjunctivitis. Psychrobacter immobilis was the most usually identified species (33.3%). The pathogen exhibited sensitivity to most antimicrobials. The most widely administered antimicrobials included cephalosporins (70%), followed by aminopenicillins and vancomycin (40%, respectively). The clinical outcome depended primarily on the infection site; mortality rate was high (44.4%), especially in cases of bacteremia (50%). Conclusion: Due to the potential of Psychrobacter spp. to cause serious infection, clinicians and laboratory professionals should consider it in the differential diagnosis in patients with infections by Gram-negative spherical bacteria, particularly in patients with significant comorbidities and immunodeficiency, in order to accurately establish the diagnosis and proceed to the right treatment. Full article

Few halophilic strains have been examined in detail for their culturability and metabolic activity at subzero temperatures, within the ice matrix, over the longer term. Here, we examine three Arctic strains with varied salinity tolerances: Colwellia psychrerythraea str. 34H (Cp34H), Psychrobacter sp. str. 7E (P7E), and Halomonas sp. str. 3E (H3E). As a proxy for biosignatures, we examine observable cells, metabolic activity, and recoverability on 12-month incubations at −5, −10 and −36 °C. To further develop life-detection strategies, we also study the short-term tracking of new protein synthesis on Cp34H at −5 °C for the first time, using isotopically labeled ¹³C₆-leucine and mass spectrometry-based proteomics. All three bacterial species remained metabolically active after 12 months at −5 °C, while recoverability varied greatly among strains. At −10 and −36 °C, metabolic activity was drastically reduced and recoverability patterns were strain-specific. Cells were observable at high numbers in all treatments, validating their potential as biosignatures. Newly synthesized proteins were detectable and identifiable after one hour of incubation. Proteins prioritized for synthesis with the provided substrate are involved in motility, protein synthesis, and in nitrogen and carbohydrate metabolism, with an emphasis on structural proteins, enzymatic activities in central metabolic pathways, and regulatory functions. Full article