Journal of Applied Microbiology最新文献

Aims: Glucosaminoglucan (β-1,4-linked glucose and glucosamine) produced by a mixotrophic sulfur-oxidizing bacterium, Thiothrix nivea, is a useful cellulose-aminating agent. Lithotrophic and mixotrophic glucosaminoglucan production were examined using fed-batch techniques.

Methods and results: A jar fermenter was used for the fed-batch cultivation. Glucosaminoglucan was extracted from T. nivea using diluted HCl. Lithotrophic growth was detected by feeding with Na2S as the energy source, and 12 mg l-1 of glucosaminoglucan was obtained. In contrast, no growth was observed with Na2S2O3. Similarly, mixotrophic growth in the presence of acetic acid was promoted by Na2S, whereas Na2S2O3 had no effect. When acetic acid and Na2S were added, 470 mg l-1 of glucosaminoglucan was obtained.

Conclusions: Thiothrix nivea was cultured, and glucosaminoglucan was produced lithotrophically using Na2S for feeding. Na2S is also indispensable for mixotrophic growth and glucosaminoglucan production, indicating that sulfide oxidation pathways control the TCA cycle. The involvement of the SOX pathway (for thiosulfate oxidation) in the activation of energy metabolism is doubtful because neither lithotrophic nor mixotrophic growth was promoted by Na2S2O3. Based on these results, we assumed that T. nivea is facultatively mixotrophic [lithotrophic growth is possible in addition to organotrophic growth in the presence of sulfide (Na2S)], rather than obligately mixotrophic.

Aims: Vulvovaginal candidiasis (VVC) is a prevalent condition affecting a significant proportion of women worldwide, with recurrent episodes leading to detrimental effects on quality of life. While treatment with clotrimazole is common, the specific alterations it evokes in the vaginal bacteriome and metabolome were previously underexplored.

Methods and results: In this prospective study, we enrolled reproductive-age women diagnosed with single VVC and conducted comprehensive analyses of vaginal fungi, bacteriome, and metabolome before and after local clotrimazole treatment. We observed a significant reduction in Candida albicans and notable improvements in vaginal cleanliness. Advanced sequencing revealed substantial shifts in the vaginal bacteriome, with an increase in Lactobacillus-dominant communities post-treatment. Our findings identified 17 differentially abundant bacterial species, including notable decreases in pathogenic anaerobes such as Gardnerella vaginalis, Dialister micraerophilus, and Aerococcus christensenii, suggesting a restoration of a healthier microbial balance. Furthermore, metabolomic analysis revealed significant changes in 230 metabolites, particularly within lipid metabolism pathways, with marked downregulation of lipid-related compounds linked to inflammation. Correlation studies indicated a strong interplay between lipid metabolites and specific bacterial species, emphasizing the influence of clotrimazole treatment on microbial and metabolic interactions. Importantly, predictive models using microbiota and metabolite signatures demonstrated high accuracy in distinguishing pre- and post-treatment states.

Conclusions: This research highlights clotrimazole's dual role in effectively clearing Candida infection and promoting a healthier vaginal microenvironment, paving the way for novel microbial and metabolomic-based diagnostic approaches to enhance VVC management and understand its underlying mechanisms.

Aims: This study investigates the traits of three plant growth-promoting (PGP) and antagonistic bacteria, Pseudomonas protegens MP12, Bacillus sp. 3R4, and Bacillus sp. T22, to assess their potential application as biocontrol agents by using the ecofriendly and low-cost substrate Corn Steep Liquor (CSL) medium. Analyses of antagonism through volatile organic compounds (VOCs) production, biofilm formation, and growth performance were carried out.

Methods and results: Dual antagonism assay showed that all strains displayed significant antagonistic activity against Botrytis cinerea through VOCs. Gas chromatography demonstrated that strains in the CSL exhibited higher VOCs production than nutrient medium. Moreover, enhanced biofilm formation analysed by Calgary Biofilm Device, growth, and biomass were noted in CSL cultures. Pseudomonas protegens MP12, which showed higher cell concentration and biomass yield, was selected for freeze-drying treatments. Storage cell viability assays evidenced that it can be effectively preserved for nearly 7 months at 4°C.

Conclusion: The results here obtained showed that CLS medium enhanced VOCs production, biofilm formation, growth, and biomass of the antagonistic bacteria of the three strains. Eventually, the more effective strain P. protegens MP12 can be stored for nearly 7 months at 4°C.

Aim: This project evaluated a biologically mediated strategy to solubilize several rare earth elements and critical raw materials, including scandium, from bauxite residue. This work seeks to expand on previous research on contact leaching with bauxite.

Methods and results: In this study, Gluconobacter oxydans was shown to secrete mixed organic acids, including gluconic acid, which was superior to pure gluconic acid in the dissolution of bauxite residue, even at low molarities. In situ contact leaching with G. oxydans significantly promoted the dissolution yield (recovery of metal present in the ore) of yttrium, aluminum, calcium, and titanium (41.18%, 67.79%, 80.16%, and 59.41%, respectively) but allowed for only marginal dissolution yield of scandium, lanthanum, cerium, and neodymium (13.40%, 14.74%, 24.41%, and 10.67%, respectively) at relatively low pulp densities. In addition, the dissolution yields of rare earth elements were reduced further with time, presumably as the oxides of these elements fell out of solution.

Conclusion: This work builds on previous research that seeks to extract rare earth elements and critical raw materials from bauxite residue through contact leaching with organic acids. Some elements such as yttrium, aluminum, calcium, and titanium could be effectively solubilized; however some elements showed reduced solubility, possibly due to tight association with the iron phase of the residue. However, the relative ease and speed of leaching, and improved solubilization, suggest that this could be a viable method for securing critical raw material supplies.

Aims: This study aimed to investigate the impact of temperature on the intestinal microbiota of largemouth bass using 16S rRNA gene amplicon sequencing, focusing on the under-explored role of abiotic factors in shaping the gut microbial community.

Methods and results: Five water temperature groups (20.0 ± 0.2°C, 25.0 ± 0.2°C, 28.0 ± 0.2°C, 31.0 ± 0.2°C, and 35.0 ± 0.2°C) were established, each with three replicates. Significant variations in intestinal bacterial community composition were observed across these conditions. Elevated temperatures (31.0 ± 0.2°C and 35.0 ± 0.2°C) led to an increase in opportunistic pathogens such as OTU180 Vibrio and OTU2015 Vogesella (P < 0.05). Species correlation network analysis showed a shift toward more positive relationships among intestinal microbes at higher temperatures (P < 0.05). Ecological process analysis highlighted a greater role of ecological drift in microbial community structure at 31.0 ± 0.2°C and 35.0 ± 0.2°C (P < 0.05).

Conclusions: The study suggests that higher temperatures may predispose largemouth bass to opportunistic pathogens by altering their intestinal microbiota. Effective water temperature management is crucial for largemouth bass aquaculture to mitigate pathogen risks and maintain a balanced intestinal microbiota. This research provides critical insights into the temperature-microbiota relationship and offers practical recommendations for aquaculture practices.

Aims: We have characterized the microbiome of infected chronic diabetic wounds (CDWs), exploring associations with antibiotic use and wound severity in a Sri Lankan cohort.

Methods and results: Fifty CDW patients were enrolled, 38 of whom received antibiotics. Tissue biopsies were analysed by microbiome profiling, and wounds were graded using the University of Texas Wound Grading System. Biofilm presence was assessed in 20 wounds. The microbiome was largely dominated by Enterobacteriaceae, Pseudomonadaceae, Streptococcaceae, and Corynebacteriaceae. Proteobacteria levels were significantly higher in antibiotic-treated wounds (P = .019), with increased Pseudomonas abundance. Wounds were categorized as grade 1 (10), grade 2 (29), and grade 3 (11). Alpha diversity varied by wound grade (P = .015), with grade 2 wounds showing the highest diversity and grade 3 the lowest. All 20 tested wounds were biofilm-positive, and community composition varied more in antibiotic-treated wounds (P = .004).

Conclusions: CDW microbiomes were dominated by Enterobacteriaceae and Pseudomonadaceae, with elevated Proteobacteria in antibiotic-treated wounds. Alpha diversity correlated with wound severity, peaking in grade 2 wounds. The high prevalence of biofilms in wounds underscores the need for management of CDWs that address microbial complexity.

Aims: To investigate and identify the antibacterial action and mechanism of rose essential oil (REO) against Aeromonas veronii isolated from Northern snakehead for the first time by the phenotypic and metabolic analysis.

Methods and results: The 2-fold broth microdilution and spread-plate method identified that the minimum inhibitory concentration and minimum bactericidal concentration of REO against A. veronii were 1.25 μl ml-1 and REO impaired the growth in a concentration-dependent manner, indicating that REO possessed a significant bacteriostatic activity. Electron microscopy and live-dead cell staining found that REO caused a severe disruption of cellular morphology and increased the membrane permeability. Additionally, REO treatment induced the leakage of intracellular biomolecules such as proteins and nucleic acids from the bacteria. Metabolomics analysis showed that compared with the control, the REO treatment group exhibited a total of 190 differential metabolites (118 down-regulated and 72 up-regulated), which involved in the main metabolic pathways such as biotin metabolism, arginine biosynthesis, glutathione metabolism, lysine degradation, and histidine metabolism and the TCA cycle. These results verified that REO disturbed the metabolic processes of A. veronii to achieve the bacteriostatic effect.

Conclusion: The rose essential oil exhibited the effective antibacterial activity against A. veronii via breaking the cellular structure, increasing the membrane permeation and disrupting the metabolic processes.

Aims: d-pantothenic acid (d-PA) is an important vitamin widely used in the feed, pharmaceutical, and food industries. This study aims to enhance the d-PA production of a recombinant Escherichia coli without plasmid and inducer induction.

Methods and results: The fermentation medium in shake flask was optimized, resulting in a 39.50% increased d-PA titer (3.32 g l-1). Subsequently, the fed-batch fermentation in a 5-l fermenter was specifically investigated. First, a two-stage temperature control strategy led to a d-PA titer of 52.09 g l-1. Additionally, a two-stage glucose feeding was proposed and d-PA titer was increased to 65.29 g l-1. It was also found that an appropriate amount of sodium pyruvate was beneficial to cell growth and d-PA synthesis. Finally, a two-stage glucose feeding combined with sodium pyruvate addition resulted in a substantially improved d-PA production with a titer of 72.90 g l-1.

Conclusion: The d-PA synthesis was significantly improved through the fermentation process established in this work, i.e. sodium pyruvate addition combined with the temperature and glucose control strategy. The results of this study could provide significant reference for the industrial fermentation production of d-PA.

Aims: This study aims to identify and address significant limitations in current culture-based regulatory methods used for monitoring microbiological water quality. Specifically, these methods' inability to distinguish between planktonic forms and aggregates containing higher bacterial loads and associated pathogens may lead to a severe underestimation of exposure risks, with critical public health implications.

Methods and results: We employed a novel methodology combining size fractionation with ALERT (Automatic Lab-in-a-vial E.coli Remote Tracking), an automated rapid method for comprehensive quantification of culturable fecal indicator bacteria (FIB). Our findings reveal a substantial and widespread presence of aggregate-bound indicator bacteria across various water matrices and geographical locations. Comprehensive bacterial counts consistently exceeded those obtained by traditional methods by significant multiples, such as an average of 3.4× at the Seine River 2024 Olympic venue, and occasionally up to 100× in irrigation canals and wastewater plant effluent. These results, supported by microscopic and molecular analyses, underscore a systematic bias in global water safety regulatory frameworks.

Conclusions: Our research demonstrates the inadequacy of traditional culture-based techniques in assessing microbiological risks posed by aggregate-bound FIB and associated pathogens, particularly in water matrices affected by FIB-rich fecal particles from recent sewer overflows or sediment, which can carry higher infectious risks. Incorporating comprehensive FIB analysis techniques, including molecular methods and rapid culture-based approaches as shown in this study, offers a promising and effective solution to these risk assessment limitations.

Aims: Lactobacilli have drawn a great deal of attention due to the heterogeneity of their cells, as well as their remarkable ability to adapt to a range of harsh conditions. One such adaptation response by Lactiplantibacillus plantarum was forming a V-shaped cell structure in low acidic pH conditions. This study aims to identify low pH induced-biofilm formation in L. plantarum and Limosilactobacillus reuteri and their antagonistic interactions with an opportunistic pathogen, Pseudomonas aeruginosa PAO1.

Methods and results: Dual species bacterial interactions revealed a Lactobacilli biofilm-mediated suppression of PAO1 biofilms and pyocyanin pigment. Furthermore, filtrates from Lactobacilli grown at low acidic pH (pH 3.5) effectively arrest the pathogenesis of P. aeruginosa PAO1, including biofilm, swarming motility, and pyocyanin formation. Liquid chromatography-mass spectroscopy analysis revealed the presence of several Lactobacilli-secreted metabolites and dipeptides that exhibited strong LasR receptor antagonistic interactions in molecular docking analysis. Prolyl-tyrosine showed the best lasR antagonistic and PAO1 biofilm inhibitory activities of the identified dipeptides.

Conclusion: Overall, the results will contribute to the development of anti-infective drugs against P. aeruginosa using Lactobacilli secreted dipeptides. Furthermore, the investigation identifies several dipeptides that can be extracted from V-shaped Lactobacilli for antimicrobial protein therapy against P. aeruginosa and other pathogens.