International Microbiology最新文献

Anti-virulence strategies are gaining recognition as promising alternatives for bacterial infection control. They act by suppressing quorum sensing circuits, disrupting biofilm formation, and inhibiting toxin production. However, the emergence of resistant bacterial mutants highlights the need for anti-virulence agents that do not induce resistance. Pseudomonas aeruginosa produces autoinducers like N-acyl-homoserine lactone (AHL), which enhance cell-population and coordinate gene expression. Plant-derived compounds, particularly O-methylated phenolic flavonoids, have shown promise in overcoming antibiotic resistance. Herein, compounds such as formononetin (isoflavone) and 4'-methoxyflavonol (flavonol) possess pharmacological properties beneficial for human health and have been found to inhibit AHL-mediated virulence factors in P. aeruginosa. These flavonoids effectively reduced the production of virulence factors like exopolysaccharides, elastase, protease, pyocyanin, and rhamnolipids assessed by biochemical assays. Motility assays demonstrated a reduction in bacterial movement, and biofilm formation was quantified and visualized using Zeiss Confocal Laser Scanning Microscopy. Gene expression analysis by RT-qPCR revealed that the flavonoids suppressed las and rhl circuits associated with virulence factor synthesis. Among the selected two compounds, 4'-methoxyflavonol exhibited the strongest inhibitory effect against P. aeruginosa. Overall, this study underscores the dual role of dietary phenolic flavonoids in supporting biological functions and serving as natural anti-quorum sensing agents, offering promising strategies to mitigate bacterial virulence.

In this work, the isolation and identification of pigment-producing fungi from substrate samples collected in the Sonoran Desert, Mexico, are described. Three fungal isolates, named CR2, SM1, and GBS, were selected for their ability to produce colored pigments. The redox properties of these pigments were characterized using UV-Vis spectroscopy and cyclic voltammetry. The GBS pigment, produced by the fungus Forliomyces uniseptata, exhibited the best electrochemical behavior, with a reversible redox cycle, indicating its potential as a redox mediator (RM) for microbial fuel cells (MFCs). The effect of different light wavelengths on the growth kinetics of F. uniseptata and pigment production was evaluated. Blue light moderately accelerated pigment biosynthesis, while darkness promoted fungal growth. Finally, the GBS pigment was tested as a RM in a MFC inoculated with Bacillus subtilis. A maximum power density of 37 μW/cm². It is suggested that mass transfer could limit performance.

Salvia miltiorrhiza is a widely used medicinal plant, and post-harvest processing methods such as sweating may influence its metabolite composition and microbial interactions. However, the metabolic and microbial changes induced by sweating remain poorly understood. This study aimed to investigate how sweating affects the metabolite profile of S. miltiorrhiza and its associated bacterial communities, with a focus on identifying key metabolic shifts and microbial dynamics. Widely targeted metabolomics was employed to compare the composition and relative content of metabolites between control (non-sweated) and sweated S. miltiorrhiza plants. Additionally, high-throughput sequencing was used to analyze variations in bacterial communities at different sweating stages. A total of 435 differentially present metabolites were identified, categorized into 11 classes, with quinones, phenolic acids, and lipids being the most prominent. Sweating significantly increased microbial diversity and richness, and we established a correlation between the accumulation of quinones and phenolic acids and shifts in bacterial community structure. Notably, sweating enhanced the levels of key metabolites, which in turn promoted the relative abundance of potentially beneficial microorganisms. Furthermore, distinct bacterial populations at different sweating stages contributed to the unique quality traits of S. miltiorrhiza. The findings demonstrate that sweating not only alters the metabolite profile of S. miltiorrhiza but also shapes its associated bacterial communities, leading to improved accumulation of bioactive compounds.

Saprolegniasis is one of the most devastating fish diseases that cause fish mortality in aquaculture in winter season, leading to economic loss to the farmers. The mycotic infection in fish occurred during the winter season in inland open water bodies due to adverse environmental factors, poor culture practices, high stocking densities, rough handling, and physiological changes associated with immune suppression. In the present investigation, we studied the environmental factors for disease progress in Pangasianodon hypophthalmus and Labeo rohita, characterization of oomycetes, and screening of potential antifungal agents against fish pathogenic oomycetes. Mortality and infection patterns have a relationship with water temperature in the present investigation. We noted that co-habitat infection was found in L. rohita and caused mortality. The presence of certain abiotic factors and susceptible host species led to the outbreak of disease in cage culture. The morphological and molecular identification of the etiological agent was carried out, and the PCR amplicon sequence of the ITS gene fragment showed similarities with Saprolegnia aenigmatica. The optimum temperature required by S. aenigmatica was between 20 and 25 °C for hyphae growth. In vitro assessment revealed that fluconazole (FLZ), boric acid (BA), and potassium permanganate (KMnO4) were unable to control zoospore colonization at higher concentrations. Clotrimazole and hydrogen peroxide inhibited colonization in 10 ppm and 100 ppm, respectively. The present investigation identified and confirmed the causative agent of saprolegniasis outbreak with associated environmental factors and approached to develop antifungal therapeutics to combat infection in the inland open-water bodies.

Faba bean (Vicia faba L.) is a major legume crop with high nutritional and commercial value, but its output is severely limited by vascular wilt and root rot caused by Fusarium oxysporum. Biological control and other environmentally benign solutions provide long-term alternatives to toxic fungicides. Under controlled conditions, the cyanobacterium Trichormus variabilis and the endophytic bacterium Priestia endophytica were tested for their biocontrol potential against Fusarium oxysporum. Plant defense responses were evaluated using total phenols, proline, and peroxidase activity. Infection with Fusarium oxysporum significantly raised stress indicators, such as phenols (71.97 mg g⁻¹), proline (5.54 mg g⁻¹), and peroxidase (6.35 U g⁻¹). Single treatments of either bioagent reduced stress, decreased phenolic buildup, and restored enzymatic equilibrium. The combination treatment offered the strongest protection, decreasing stress indicators to 58.9 mg/g phenols, 3.42 mg/g proline, and 4.54 U/g peroxidase. Bioagents increased soil microbial activity, including dehydrogenase (4.69 mg TPF g⁻¹ soil in Trichormus variabilis vs. 2.5 in Fusarium oxysporum), chitinase (4.07 U mL⁻¹ in the combined treatment vs. 1.40 in control), and protease (4.50 U g⁻¹ soil in the combined treatment vs. 1.70 in control). The enzymatic stimulation increased plant health and resistance. Trichormus variabilis and Priestia endophytica had a synergistic impact against Fusarium oxysporum, making combination application the most promising technique for long-term management of faba bean root rot.

Alkaline pectinases are pivotal for sustainable industries such as textile scouring, juice clarification, and wastewater treatment; however, strains combining high catalytic activity, true alkalistability, and broad agro-industrial applicability remain scarce. Thirty pectinolytic isolates obtained from decayed fruits in Sidi Bel Abbes, Algeria, yielded three Bacillus amyloliquefaciens strains (SPR6, ST9, SC2) with superior enzyme productivity. Under optimized submerged fermentation (pH 9.0, 37 °C, 48 h), strain ST9 achieved 22.4 U/mL, a 1.78-fold increase over baseline, while replacing commercial pectin with orange peel enhanced yield by 1.32-fold and reduced substrate costs by 99%. The strains exhibited remarkable polyextremotolerance, maintaining viable growth and residual enzymatic activity under abiotic stress conditions (up to pH 12, 50 °C, and 11% NaCl), beyond their optimal production range. Beyond pectinolysis, all isolates co-produced key hydrolases, expressed plant-growth-promoting (PGP) traits (indole-3-acetic acid, siderophores, phosphate solubilization), and suppressed Fusarium and Aspergillus spp. This first report of alkaline-adapted B. amyloliquefaciens producing industrially robust pectinase and exhibiting PGP potential highlights their promise as dual-purpose biocatalysts and bioinoculants for circular-bioeconomy applications.

This study evaluates the antibacterial, antibiofilm, and anti-quorum-sensing (QS) properties of ilimaquinone (IQ) against Gram-positive and Gram-negative pathogens. The agar cup diffusion method revealed significant bacterial inhibition, with minimum inhibitory (MIC) and bactericidal (MBC) concentrations ranging from 6.25 to 25 μM and 12.5 to 50 μM, respectively. IQ exhibited dose-dependent biofilm inhibition, demonstrating its potential as an anti-biofilm agent. QS inhibition was assessed by pigment suppression in Chromobacterium violaceum (violacein), Serratia marcescens (prodigiosin), and Pseudomonas aeruginosa (pyocyanin, pyoverdine), reducing their production by 73.33%, 53.68%, 57.13%, and 62.42%, respectively, at sub-MIC concentrations. IQ also inhibited QS-regulated virulence factors in P. aeruginosa, including LasA protease, elastase, rhamnolipid, and extracellular polymeric substance (EPS) production, disrupting biofilm formation. Molecular docking and dynamics analysis confirmed strong binding affinities of IQ to key QS and biofilm-associated proteins (EsaI, PilY1, LasA, PilT, LasR, RhlR, LasI, PqsR, CviR, and CviR'), highlighting its mechanistic role in QS inhibition. These findings suggest that IQ is a promising antibacterial and anti-QS compound with potential therapeutic applications for managing bacterial infections and biofilm-related complications.

Drought stress poses a severe threat to tea plantations globally, leading to a significant reduction in yields. Use of plant growth-promoting bacteria (PGPB) has emerged as a promising strategy to alleviate the detrimental effects of water stress. This study investigates nine distinct bacterial strains, isolated from a drought-prone region in North-East India, for their plant growth-promoting (PGP) traits and their ability to mitigate osmotic stress. These strains were identified based on morphological characteristics and 16S rRNA molecular analysis. Among them, the strains-Chryseobacterium bernardetii (S₄), Cytobacillus gottheilii (S₅), Kitasatospora aureofaciens (S₇), Kocuria palustris (A), and Brachybacterium rhamnosum (B)-exhibited higher PGP activities under osmotic stress conditions (- 0.19 MPa and - 0.93 MPa induced by PEG-6000). Additionally, K. palustris (A) and B. rhamnosum (B) demonstrate effective adaptation to oxidative stress by reducing proline accumulation and were also found to be catalase (CAT) positive. The effect of these osmotolerant PGPBs was further evaluated on tea seedlings under drought stress. Pot experiments in nursery were conducted with three treatments: a positive control (plants watered frequently), a negative control (no treatment), and eight treatments (T1-T8: bacterial inoculations). When comparing the efficacy of bacterial isolates and delivery methods-bioencapsulation and soil drenching. Treatment T6 (comprising strains S₄, S₅, S₇, A, and B) inoculation via soil drenching method improved drought tolerance by effectively modulating osmolyte concentrations, as evidenced by a reduction in total soluble sugars compared to the negative control, highlighting their potential role as bioformulation enhancing osmotolerance and alleviating drought stress in tea plants.

Microalgae are a rich source of valuable products like astaxanthin, a health-promoting ketocarotenoid, but their carotenoid production is challenging due to demanding culture conditions. Consequently, an attempt was made to isolate and screen a new microalgae strain for astaxanthin production via a two-stage cultivation method. In the first stage (vegetative phase), a nutrient-rich medium was used to promote cell growth and biomass, and in the second stage, astaxanthin accumulation was stimulated by stress conditions (0.2% NaCl and 4.4 mM sodium acetate) with continuous light illumination. The effect of physicochemical factors on cell growth, chlorophyll, and carotenoid content was intensively investigated. The microalgal strain was genomically identified as Desmodesmus sp. PLM2 using 18S rRNA sequencing. Optimised conditions, i.e. 20 mM sodium nitrate, 3 mM glucose, 32 mM potassium chloride, pH 7, and temperature 27 °C yielded a maximum biomass of 4.7 g/L, total chlorophyll content of 27.13 µg mL^-1, and total carotenoid content of 7.88 µg mL^-1. Further, in the red stage, stress induction led to the accumulation of carotenoid in the PLM2 strain. A comprehensive identification of the compound was done using various techniques including UHPLC, FT-IR, and Raman spectroscopy, all of which indicated towards the presence of astaxanthin. The strain Desmodesmus sp. PLM2 produced 20.2 mg/L of astaxanthin as per the UHPLC chromatogram. This study showed that Desmodesmus sp. PLM2 can be grown in two stages using the ideal physicochemical conditions, which could significantly aid in the industrialisation of microalgae for astaxanthin production.