Journal of Applied Microbiology最新文献

Aims: The present study aimed to explore microbial production of neurotransmitters related to cognitive function in the faecal microbiota of healthy older adults, and assess whether a multi-strain probiotic formula may influence production of these neuroactive metabolites, short-chain fatty acids, and the bacterial community.

Method and results: The current study employed a three-stage continuous culture system with faecal microbiota from three healthy older adult donors. Neuroactive compounds were quantified using liquid chromatography mass spectroscopy, SCFAs using gas chromatography, and the bacterial community was assessed using fluorescence in situ hybridization with flow cytometry and 16S rRNA sequencing. Addition of the probiotic supplement (Bifidobacterium lactis W51, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus salivarius W24, Lactobacillus casei W56, Bifidobacterium bifidum W23, Lactobacillus brevis W63, Lactococcus lactis W19, Lactococcus lactis W58) significantly increased the relative abundance of Lactococcus lactis in the transverse region, alongside a trend for increased Roseburia across the three colon regions modelled, valerate in the distal region, and GABA in the proximal region.

Conclusions: While administration of the probiotic only had a small effect of trending increases in the synthesis of GABA and valerate, this highlights important mechanisms by which probiotics could be involved in the gut-brain axis. The model also enabled the observation of limited microbial production of other neurotransmitters. Further exploration in human studies is therefore warranted. Probiotics were confirmed to lead to microbial changes, both directly (Lactococcus) and indirectly (Roseburia). This research helps to support mechanistic understanding of probiotics and the gut-brain axis.

Aims: This study aimed to elucidate the dynamics of soil microbial communities during ecological restoration on degraded mountain slopes, specifically comparing the impacts of two common strategies: aggregate spray-seeding and planted forest establishment, against undisturbed natural slopes, and assessing key drivers of microbial recovery.

Methods and results: Soil microbial community composition (bacteria and fungi), diversity, and co-occurrence network structure were analyzed 7 years after restoration initiation. Both restoration approaches facilitated microbial community recovery, with restored slope compositions converging towards natural slope baselines. Fungal communities exhibited greater OTU diversity than bacteria, attributed to engineered substrates and rapid vegetation stabilization from spray-seeding. Crucially, restoration successfully increased microbial network complexity. Spray-seeding specifically achieved network stability comparable to natural ecosystems. Significant environmental relationships were identified: soil water content (SWC) showed negative correlations with fungal richness and composition, while belowground biomass (BGB) positively correlated with bacterial composition.

Conclusions: Restoration effectively promotes soil microbial community recovery towards natural ecosystem states, albeit with distinct dynamics for bacteria and fungi. Fungal communities are particularly responsive to restoration techniques like spray seeding. Soil properties (SWC) and plant development (BGB) are pivotal drivers shaping microbial assemblage during restoration.

Aims: Chelating agents are metal-sequestering compounds with antibacterial properties suitable for commercial and therapeutic applications. This study investigated the involvement of metal restriction and membrane disruption in the antibacterial mode of action of three chelators.

Methods and results: The antibacterial, metal sequestration, and membrane disruptive effects of ethylenediaminetetraacetic acid, diethylenetriamine pentamethylene phosphonic acid, and fusaric acid were examined across five bacterial species. ICP-MS was used to determine the impact on bacterial metal composition, while RT-qPCR of selected genes allowed evaluation of changes in cellular responses to intracellular metal depletion. Mutants defective in metal import and export machinery were also examined to validate processes critical for resistance. Chelator-mediated disruption of membranes was investigated using 1-N-phenylnapthylamine and propidium iodide. Finally, the capacity of two of the chelators to potentiate the activity of ampicillin, chloramphenicol, tetracycline, and three aminoglycosides was assessed in chequerboards. The results show that these chelators restrict access to iron, zinc, manganese, and calcium to varying degrees in these bacterial species, reflecting important differences in envelope architectures and metal handling capabilities.

Conclusions: This study shows that all three chelators behave differently in restricting metal access and possess antibacterial properties that often act synergistically in combination, notably with other antimicrobials.

Aims: Non-alcoholic fatty liver disease (NAFLD) is a prevalent chronic liver condition, affecting 25% of adults globally, with risks of progression to severe complications such as cirrhosis and hepatocellular carcinoma. Emerging evidence highlights gut microbiota dysbiosis in NAFLD pathogenesis, suggesting probiotics as promising interventions. This study aimed to evaluate the potential of Lacticaseibacillus paracasei HP-B1337 as a probiotic for NAFLD management through phenotypic, genotypic analyses, and in-vivo mouse model.

Methods and results: The strain L. paracasei HP-B1337 was identified using colony morphology, physiological and biochemical characterization, carbon utilization tests, and whole-genome sequencing. Its safety profile was assessed via minimum inhibitory concentration testing, genotype-based antibiotic resistance analysis, biogenic amine production assays, and genetic screening for virulence and pathogenic factors. Probiotic properties, including acid and bile salt tolerance, antimicrobial activity against pathogens, adhesion capacity, and beneficial gene identification, were investigated. Additionally, the anti-NAFLD potential of HP-B1337 was validated in a high-fat diet (HFD)-induced mouse model. The results demonstrated that HP-B1337 exhibits robust probiotic characteristics, a favorable safety profile, and significant efficacy in alleviating HFD-induced fatty liver disease in mice.

Conclusions: Findings of this study provide strong evidence supporting the candidacy of HP-B1337 as a probiotic for NAFLD management.

Aims: The control of the common cockchafer Melolontha melolontha using the entomopathogenic fungus (EPF) Beauveria brongniartii is one of the most successful biological control systems. This study aimed to identify factors influencing the outcome of laboratory bioassays, which are crucial early steps in the development of biocontrol products, by using this system as a role model.

Methods and results: We combined spray and injection applications of conidio- and blastospores of the host-specific pathogen B. brongniartii BIPESCO2 (Bip2) and the generalist EPF Metarhizium brunneum Ma 43 and applied the treatments to cockchafer adults and larvae. Furthermore, the mycotoxin oosporein was tested alone or with Bip2 blastospores, as well as Bip2 conidiospores, in immersion, spray, and injection treatments of larvae. The most efficient spore suspension was applied to different larval body parts and to their food. Bip2 and Ma 43 infected adults frequently, but larvae resisted topical spray applications. Injection treatments revealed that adult cuticles offered limited protection, whereas the larval cuticle acted as an effective barrier. Larval thorax and legs, with articulations and intersegmental membranes, were more susceptible than the abdomen. Oosporein synergized with blastospores in larval immersion treatments, but alone had no effect. We propose that oosporein's antibiotic activity disrupts the larval cuticle microbiome, facilitating infection.

Conclusion: Contrary to the assumption that laboratory bioassays overestimate EPF performance under field conditions, we found the opposite. We therefore argue that more elaborate studies are required for realistic evaluation of candidate biocontrol agents, considering host-pathogen traits and test conditions.

Aims: Phenazine-1-carboxylic acid (PCA) is an important secondary metabolite and a precursor for the biosynthesis of many phenazine derivatives, with highly efficient antifungal activity and environmentally friendly characteristics, which is mainly produced by microbial fermentation. Therefore, it is of great importance to isolate and identify new chassis strain with higher PCA production to meet the demand of PCA-efficient synthesis. In this study, a wild-type strain named DZ15 was initially characterized, which displayed the highest PCA production among all of wild-type strains reported. However, its physiological characteristics and metabolic performance remain unclear.

Methods and results: First, the taxonomic classification of strain DZ15 was initially identified through 16S rRNA-based phylogenetic analysis and subsequently classified as Pseudomonas chlororaphis subsp. aureofaciens. Then, genomic characteristics of P. chlororaphis DZ15 were investigated through comparative genomic analysis with P. chlororaphis GP72, LX24, and HT66 based on COG analysis and KEGG analysis. Furthermore, to explore the reasons for higher PCA production in P. chlororaphis DZ15, the expression level of the phenazine cluster promoter (Pphz) from P. chlororaphis DZ15 and other three strains (i.e. GP72, LX24, and HT66) was detected and compared in P. chlororaphis DZ15 and GP72 using a green fluorescent protein (GFP) fusion reporter. Among the four Pphz promoters, Pphz from P. chlororaphis DZ15 displayed the highest expression level, about 25413.44 AU/OD600. However, the expression level of all four promoters showed no significant difference in P. chlororaphis GP72 and much lower than their expression level in P. chlororaphis DZ15 with less than 5000 AU/OD600. Finally, the production of PCA was further improved from 370.14 mg·L-1 to 1532 mg·L-1 by deleting modifier gene phzO and negative regulatory genes rpeA, rsmE, and lon.

Conclusion: Our study firstly investigated the genomic characteristics of wild-type strain with the highest PCA production (i.e. P. chlororaphis DZ15) through whole-genome sequencing analysis. Then, our results indicated that the high expression level of phz cluster promoter and physiological characteristics of P. chlororaphis DZ15 both contributed to its high PCA production. Furthermore, PCA production in P. chlororaphis DZ15 was enhanced through genetic modification.

Aims: A standardized approach to mimic real-world surface wear is critical for assessing disinfection performance in practical applications. This study developed a reproducible method to simulate surface damage and evaluate its effect on disinfectant efficacy.

Methods and results: First, we developed a novel and reproducible method to standardize surface scratching and simulate worn surface roughness. This was achieved by modifying a Sutherland Rub Tester® with sandpaper, calibrated weight, and controlled abrasion cycles, allowing consistent replication of surface damage for experimental evaluation. Second, we adapted a standardized EPA method to compare disinfection efficacy against Pseudomonas aeruginosa and Staphylococcus aureus biofilms on scratched and nonscratched stainless steel (SS) and high-density polyethylene (HDPE) coupons, treated with three disinfectant products: hypochlorite (CL), hydrogen peroxide (HP), and quaternary ammonium (QA). Surface roughness increased by 0.82 µm (SS) and 12.69 µm (HDPE) after 80-grit sandpaper treatment. Biofilm reductions following three disinfectant treatments ranged from 3.23 to 6.22 logs (P. aeruginosa) and 2.92-5.62 logs (S. aureus) for all coupon types, with surface roughness having no significant impact on disinfection efficacy. A 6-log reduction was achieved only with CL against P. aeruginosa on nonscratched HDPE.

Conclusion: This study developed a reproducible surface-scratching method and found that biofilm disinfection was affected by bacteria, surface material, and disinfectants.

Aim: To characterize and compare the bread-making practices and microbial diversity of traditional and bakery sourdoughs from Lebanon and determine how specific practices shape microbial diversity.

Methods and results: Thirty bread-making practices variables from 26 Lebanese bakers were analyzed using Multiple Correspondence Analysis (MCA) and hierarchical clustering, which revealed three distinct bread-making groups. The first group (wheat flour sourdough) was characterized by the use of wheat flour, frequent backsloppings, high hydration, and fermentation temperatures. The second group (wheat flour Epiphany sourdough) included traditional household practices involving non-backslopped fermented sourdough with lower hydration and fermentation temperatures. The third group (maize flour sourdough) was distinguished by the use of maize flour during sourdough making. Metabarcoding (V3V4 and ITS1) of 50 sourdoughs revealed 141 fungal and 98 bacterial species. In parallel, 351 yeast strains were isolated and identified, providing a valuable Lebanese genetic resource. PERMANOVA on weighted_UniFrac distance clustered bacterial and fungal communities into three significantly different groups, associated with bread-making practices. Non-backslopped "wheat flour Epiphany" sourdoughs exhibited a significantly higher Shannon index compared to the two other sourdough groups. Their microbial communities were characterized by the presence of various bacterial and fungal families, including Enterobacteriaceae, Pseudomonadaceae, Erwiniaceae, Lactobacillaceae, and several filamentous fungi. In contrast, regularly backslopped sourdoughs were dominated by Fructilactobacillus sanfranciscensis and Saccharomyces cerevisiae. These differences in microbial community could be statistically linked to several factors, including temperature and hydration, which were higher in regularly backlopped sourdoughs.

Conclusion: This study provides the first comprehensive analysis of contrasted sourdough bread-making practices and microbial species diversity in Lebanon and highlight how variations in backslopping practices can significantly influence microbial species diversity and composition in traditional sourdoughs.

The estimated time since death, or postmortem interval (PMI), is a crucial piece of information in forensic death investigations. Current scientific methods used to estimate this timeframe do not always provide the most accurate predictions and often rely on subjective interpretations. The microbiome has recently been recognized as a large impactor of human decomposition and current research shows its potential to provide additional accuracy to PMI estimations. As bacteria are ubiquitous, persistent, and due to recent advancements in technology genetically identifiable, microbial analysis effectively complements other forensic science approaches. However, this new field of forensic research requires standardization, foundational validity, and research collaboration if it is to be considered reliable for use as evidence in the court of law. This review discusses the potential for forensic microbiology to be used as an additional estimator for the PMI, the advantages of epinecrotic microbiome sampling, and outlines further steps needed for the integration of this discipline into forensic practice.

Aims: Our aim was to evaluate the antileishmanial potential of Shikonin (SKN), a natural topoisomerase inhibitor derived from Lithospermum erythrorhizon, against Leishmania donovani and to elucidate its mechanism of action through physiological, ultrastructural, and in silico studies.

Methods and results: SKN inhibits the in vitro proliferation of both parasite forms, with IC50 values of 3 μM for promastigotes and 0.75 μM for intracellular amastigotes. Using a combination of biophysical and biochemical methods, we found that SKN exerts its cytotoxic effect by generating oxidative stress, mitochondrial dysfunction, and nuclear damage, leading to apoptotic cell death in the parasites. Ultrastructural analysis revealed morphological alterations and apoptotic features in treated parasites, which included mitochondrial swelling and organelle damage, nuclear pyknosis, and pronounced nuclear membrane swelling in the parasites. Since the unique bi-subunit topoisomerase of these parasites has structural differences from the human counterpart and is considered a potential drug target, we performed in-silico molecular docking studies to determine the binding affinity of SKN with topoisomerase 1B (TOP1B). SKN exhibits a stronger binding affinity with L. donovani 1B than the standard topoisomerase inhibitor, camptothecin, forming favorable interactions at the catalytic site. It also shows a lesser binding affinity with human TOP1B than camptothecin.

Conclusions: Targeting the Leishmania parasite Topoisomerase with the natural naphthoquinone SKN inhibits parasite proliferation. SKN generates oxidative stress, leading to mitochondrial dysfunction, elevation of cytosolic calcium, and nuclear damage resulting in apoptotic cell death.