International Microbiology最新文献

Acinetobacter baumannii, a pathogen for humans and animals, possesses a tremendous potential to survive under hostile conditions. We studied the effect of temperature, nutrient deprivation, and desiccation on the survival of A. baumannii ATCC 19606^T by monitoring variations in cellular counts and in cell length and analyzing cell envelope subproteome during the survival process. Nutrient deprivation alone does not appear to have a negative effect on A. baumannii survival, but incubation at 37 °C in an aqueous solution provoked loss of culturability, as well as a marked increase in cell length. Although a high stability of the membrane subproteome was observed, even under environmental conditions that promote morphological changes and loss of culturability, the expression of some membrane proteins did change upon exposure to the stress. Signal peptidase I and fimbrial protein became undetectable in almost all the conditions examined, while EF-Tu (in all conditions) and MinD (in populations incubated at 37 °C) were overexpressed. The great capacity for survival displayed by A. baumannii under adverse conditions may be explained, at least in part, by its capacity to maintain the expression levels of most of its cell envelope proteins and regulate a few others.

Spent yeast represents a promising opportunity for value-added applications. This study proposes its biofortification as a source of organic selenium (Se)-enriched supplements. Se is an essential component of the glutathione (GSH) system, playing a critical role in decomposing lipid peroxidation products and protecting cellular membranes. We evaluated the effects of sodium selenite (Na₂SeO₃) supplementation on enzymatic activity, oxidative stress markers, and biomass production of Saccharomyces cerevisiae Thermosacc^®, cultivated in corn hydrolysate-a non-synthetic medium that provides a more realistic representation of industrial environments-under aerobic and anaerobic conditions. Antioxidant responses were assessed via glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione S-transferase (GST) activities, while oxidative stress was measured through hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels. Yeasts were grown with 0, 200, and 400 mg L^-1 Na₂SeO₃. The highest enzymatic activities were observed in AE400 (GPx: 5.35 μmol mg^-1, GR: 3.39 μmol mg^-1, GST: 0.035 μmol mg^-1), indicating enhanced antioxidant defenses under aerobic Se supplementation. However, increased Se concentrations also elevated H₂O₂ and MDA levels-especially in aerobic conditions-likely due to intensified ROS generation. Consequently, biomass production and growth parameters declined, suggesting an energy trade-off in which antioxidant defense is prioritized over cell proliferation. These findings highlight Se's dual role as both an antioxidant and a pro-oxidant at elevated concentrations. This study advances understanding of yeast redox biology and supports the integration of Se-enriched yeast production into industrial fermentation as a sustainable strategy for generating high-value functional ingredients for food and feed applications.

Global climate change has posed significant challenges to the aquaculture industry, leading to the emergence of novel diseases. A recently emerging disease, termed the overwintering syndrome, has been reported in freshwater fish aquaculture systems in China during the winter-spring transition. This syndrome is characterized by weight loss, decreased activity levels, and mass mortality. Currently, little is known about cause of the emerging disease. In this study, the gut microbiota of healthy and diseased channel catfish (Ictalurus punctatus) were analyzed using metagenomic sequencing. Diseased fish exhibited a notable reduction in bacterial diversity compared to healthy controls, while the viral richness was significantly higher. Additionally, random forest models based on gut microbiota composition revealed high accuracy in distinguishing between diseased and healthy fish. Several gut microbiota biomarkers with potential diagnostic value were identified, primarily consisting of rare taxa (relative abundance < 5%), except for Alphaproteobacteira, Siphoviridae and Podoviridae. Furthermore, an increase in the prevalence and abundance of pathogens was observed in the intestines of diseased fish compared to healthy counterparts. Notably, Vibrio cholerae and Dickeya dadantii were enriched in the intestines of fish exhibiting the overwintering syndrome. Concurrently, genes involved in the synthesis of innate immune factors was markedly diminished in the gut microbiota of diseased fish, along with a reduction in the microbial hosts of these genes. Collectively, these findings elucidate the enrichment of pathogens and the attenuation of innate immunity in fish with the overwintering syndrome, correlating with alterations in the gut microbiota.

Bacillus cabrialesii HB7, a novel halotolerant strain isolated from Qatari soil, can effectively promote tomato plant growth and mitigate saline stress and has a great biofertilizer potential. Due to its promising agronomical and biotechnological potential, high spore densities should be achieved, to extend its use. In this study, culture conditions were optimized with different methods to improve HB7 spore production. Firstly, three culture media were tested to find the best medium for high spore density. When using the semisynthetic medium supplemented with 15 g.L^-1 NaCl, high spore production was achieved compared to complex medium and G10 media with and without NaCl addition. Secondly, key fermentation parameters were determined by Plackett-Burman design, and the optimum levels of six components (yeast extract, KH₂PO₄, casein hydrolysate, (NH₄)₂SO₄, NaCl concentrations, and pH) were optimized with a hybrid design, achieving 1.82 × 10⁹ spore.mL^-1 and a threefold spore production improvement, when compared to the basal medium. Moreover, HB7 exhibited faster cell growth (0.97 h^-1 vs. 0.53 h^-1) and glucose uptake (1.09 h^-1 vs. 0.89 h^-1) after optimization. These findings may play a pivotal role in the synthesis of an effective biofertilizer based on B. cabrialesii HB7 for sustainable agriculture and biotechnological advancements.

Rice blast, caused by Magnaporthe oryzae, remains a major constraint to global rice production, typically presenting as necrotic lesions on infected leaves. To investigate the bacterial communities associated with these lesions, we employed a novel "Microbiome Imprinting-Metabarcoding" approach, which generated comprehensive microbial datasets (203.34 Mb) from two blast-infected rice cultivars, aromatic Pusa Basmati 1 (PB1) and non-aromatic VL Dhan 85. Metabarcoding analysis revealed the consistent presence of several dominant bacterial genera, including Pantoea, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Pseudomonas, and Chryseobacterium, across both cultivars. Notably, bacterial diversity was reduced in blast lesions compared to healthy phylloplane tissues. Lesion samples comprised 28 genera (Shannon Diversity Index: 1.66; Chao1 richness: 326.86), whereas healthy leaves harbored 48 genera (Shannon Diversity Index: 1.98; Chao1 richness: 361.82). Linear discriminant effect size (LEfSe) analysis identified specific genera such as Bifidobacterium, Desemzia, Acidovorax, and Mucilaginibacter that were uniquely associated with the dysbiotic microbial communities in infected tissues. Core microbiome analysis further revealed ten genera shared between both cultivars, with Pantoea and Allorhizobium emerging as the most abundant. These findings offer new insights into the composition and dynamics of lesion-associated bacterial communities in rice blast and highlight potential microbial targets for the development of improved disease management strategies.

The industrial development and modernization occurring worldwide are crucial for meeting the demands of the present era. However, the necessary use of xenobiotics, such as heavy metals, dyes, and pesticides, poses a significant threat to ecosystems and inflicts severe harm on the environment. Cyanobacteria play a vital role in nitrogen fixation and are integral to the environment, contributing to soil fertility, UV protection, and oxygen production, among other functions. Despite the ability of these microbes to produce valuable metabolites, their production is sensitive to environmental toxicity. Furthermore, the relationship between photonic wavelength and the photosynthetic activity of cyanobacteria remains poorly understood. This article investigates the connection between the efficiency of the photosystem and the nature of the incident photonic wavelength. Additionally, the study examines the effects of photonic energy on the response of cyanobacteria to Cr (VI) toxicity, highlighting the involvement of an alternative quantum well induced by the presence of Cr (VI). Significantly, the research identifies a clear correlation between the level of photonic energy and the efficiency of the photosystem by calculating various photochemical and physiological parameters, including pigments, dry biomass, quantum yield, and transient S state. The enhancement of water-splitting processes and photosystem II efficiency was also observed with increased photonic energy under blue and green light, leading to a reduction in oxidative damage. These findings suggest a cooperative relationship between specific light wavelengths and the alleviation of Cr (VI) stress in Nostoc commune, providing insights into their ecological adaptability and potential applications in controlled cultivation systems and bioremediation.

The study investigates the microbial composition of bat flies (Diptera: Nycteribiidae) collected from Myotis punicus in Algeria, focusing on the diversity and dynamics of their microbiota through network analysis. The analysis targets two genera, Nycteribia and Penicillidia, comparing oioxenous and stenoxenous species to understand host specificity's influence on microbial communities. Utilizing 16S rRNA sequencing, alpha and beta diversity metrics, and co-occurrence networks, the study assesses microbial diversity, community composition, and the impact of specific bacteria (endosymbionts, commensals, and pathogens) on network stability. Results reveal significant microbial community variations between genera and species, with N. latreillii exhibiting the most complex network. We showed that host specificity and feeding strategies significantly influence microbial diversity and interactions within bat flies. Robustness analysis through node removal simulations identifies the roles of key bacteria, such as Wolbachia, Arsenophonus, and Bartonella, in maintaining network stability. Findings highlight the complex interplay between these microorganisms and their hosts, offering insights into microbial ecology and vector-pathogen dynamics. The research underscores the importance of bat flies in shaping pathogen transmission networks, contributing valuable knowledge to wildlife ecology, disease control, and conservation strategies.

Malabar spinach (Basella alba L.) is a widely consumed leafy vegetable in Vietnamese daily meals. It has a short growth cycle but is susceptible to various diseases, of which the nematode Meloidogyne spp. is a significant factor causing yield reduction. This study focused on finding native plant growth-promoting rhizobacteria that can control root-knot nematodes and stimulate plant growth. The results isolated and selected Bacillus velezensis BHMT4.1, Staphylococcus carnosus CCMT2.1, and Pseudomonas fluorescens HMMT1.1, which showed promise in controlling Meloidogyne spp. in Malabar spinach and promoting plant growth. In the in vitro experiment, the B. velezensis BHMT4.1 strain caused the highest immobilization of J2 with 68.67%, followed closely by the P. fluorescens HMMT1.1 strain with 66.67%. The S. carnosus CCMT2.1 strain inhibited nematode egg hatching after 7 days, achieving a rate of 42.67%, while B. velezensis HMMT1.1 reached 44%. In addition, the B. velezensis BHMT4.1 strain demonstrated the best ability to produce siderophores on CAS agar after 48 h. The P. fluorescens HMMT1.1 strain exhibited the highest nitrogen fixation ability after 3 days of culture on the NFb medium. In greenhouse trials, Malabar spinach was inoculated with the S. carnosus CCMT2.1, reducing the number of galls to 16.29% in comparison to the control, which stood at 91.88%. Additionally, the nematode density in the soil decreased to 45.20 individuals compared to the control of 66.66 individuals (nematodes/50 g soil) after 28 days. This study showed that native bacterial strains found in vegetable soil have the ability to enhance plant development and protect Malabar spinach from being attacked by Meloidogyne spp. The results suggest that these bacterial strains could be further developed into potential biopesticides to help reduce root-knot nematode damage. Additional field studies are necessary to assess how well these bacteria adapt to the rhizosphere ecosystem of vegetable plants.

Soil salinization is a critical constraint on global rice production, posing a serious threat to food security and underscoring the urgent need for sustainable strategies to fortify plant stress resilience. In this context, this study demonstrates that SB24, a halotolerant PGPR isolated from saline rice fields, markedly improved the salinity tolerance of rice genotype Pusa 44 through coordinated physiological, biochemical, and molecular responses. This strain, identified by 16S rDNA sequencing, exhibited high salt tolerance (up to 16% NaCl) and possessed multiple plant growth-promoting traits. Under 125 mM NaCl stress, SB24 inoculation enhanced germination and growth, with significant increases in shoot and root biomass compared to uninoculated controls. SB24-treated plants showed elevated photosynthetic pigments (Chl a, Chl b, carotenoids), soluble sugars, and soluble proteins, alongside enhanced antioxidant enzyme activities (SOD, CAT, APX, PPO) significantly. These changes were accompanied by reductions in oxidative stress markers, including electrolyte leakage, H₂O₂ accumulation, lipid peroxidation, and lipoxygenase activity. SB24 also promoted osmolyte accumulation (proline, glycine betaine and maintained ion homeostasis by reducing Na⁺ uptake while increasing K⁺ and Ca^2⁺ retention. At the transcriptional level, SB24 upregulated the expression of key salt-responsive genes, including OsSOS1 (salt overly sensitive 1) 1.35-fold, OsNHX1 (vacuolar Na⁺/H⁺ antiporter 1) 1.5-fold, OsHKT1;5 (high-affinity K⁺ transporter 1;5) 1.23-fold, OsFeSOD (iron superoxide dismutase) 1.22-fold, and OsAPX (ascorbate peroxidase) 1.18-fold, validating the observed physiological, and biochemical responses to improved salt stress tolerance. Taken together, these findings establish SB24 as a potent bioinoculant with strong potential for mitigating salinity stress through integrated, multi-level mechanisms.

Gamma-aminobutyric acid (GABA) is a sedative drug capable of alleviating anxiety disorders, but its synthetic preparation is characterized by poor stability and insufficient bioavailability, along with its high cost. In this study, its precursor glutamic acid decarboxylase (GAD) from Lactobacillus casei IIB-09 was immobilized on biodegradable mesoporous silica nanoparticles (MSNPs) to improve the enzyme's catalytic efficiency and bioavailability, while providing a cost-effective synthetic approach. Under optimized culture conditions, i.e., 0.5% (w/v) monosodium glutamate (MSG) at pH 6.5 for 48 h with an inoculum size of 2% (v/v), the highest GAD activity (3.59 ± 0.01 IU/mL/min) and concentration of GABA (137 ± 0.01 mM) were achieved. GAD was physically immobilized onto biodegradable MSNPs and subsequently characterized using various analytical techniques. To confirm the crystalline nature of MSNP, X-ray diffraction (XRD) analysis was performed. Further, UV-Vis, SEM, and FTIR spectra verified the immobilization of GAD on MSNPs. After optimization of the immobilization process, the immobilized enzyme showed a twofold increase in activity (2.59 ± 0.03 IU/mL). A comparative analysis was done to examine the thermophilic characteristics and the activity of both free and immobilized enzymes under varying concentrations of methanol and α-ketoglutarate. The free and immobilized GAD exhibited maximum GABA production (112 ± 0.02-119 ± 0.03 mM) at 45 °C. This study highlights the true potential of immobilized GAD as a sustainable approach for its efficient biotransformation into GABA for applications in the pharmaceutical and functional food industries.