Journal of Applied Microbiology最新文献

Aims: The sand-fixing desert shrub Artemisia sphaerocephala produces a large amount of seed mucilage, which plays crucial roles in the adaptation of this species to desert environments. Seed mucilage has been shown to be degraded by Phanerochaete chrysosporium from habitat soils, but the process and products of this degradation remain unclear. To fill this gap, we explored the factors and processes involved in mucilage degradation.

Methods and results: We found that P. chrysosporium had the ability to produce iron carriers and to solubilize potassium and phosphorus. Mucilage degradation was affected by multiple factors, and the optimum conditions for mucilage degradation were 30°C, pH 4.5, 10 ml of fungal solution, and 1.0 g of mucilage substrate, with a degradation rate of 93.04% ± 4.87% at 20 days. The untargeted metabolome screened 300 significantly different metabolites during mucilage degradation, of which 291 were upregulated and 9 downregulated. The main degradation products were organoxides, lipids, lipid-like molecules, phenylpropanoids, polyketides, and organic acids. The most significantly affected pathway was the valine, leucine, and isoleucine biosynthetic pathway.

Conclusions: Our study has elucidated the mucilage degradation process and metabolites, which may help us to better understand the ecological functions of seed mucilage and the mechanisms of plant-microbe interactions in deserts.

Aims: This study aimed to assess the mode of action of fusaric and 9,10-dehydrofusaric acids on cell respiration by measuring the hyphal oxygen consumption rate, and the effects on cell membrane integrity by determining the electrical conductivity of the mycelium.

Methods and results: Bioactivity-directed fractionation of the active culture medium and mycelium organic extracts from the Fusarium lactis strain SME13-2 isolated from Sapium macrocarpum led to the isolation of two known alkylpicolinic acid derivatives: fusaric acid and 9,10-dehydrofusaric acid, along with the known polyketide bikaverin. Fusaric acid and 9,10-dehydrofusaric acid exhibited antioomycete and antifungal activities, significantly inhibiting the radial growth of Phytophthora capsici, Pythium aphanidermatum, Alternaria alternata, and F. oxysporum. Additionally, they induced changes in colony morphology and negative effects on the ultrastructure of their hyphae. To date, the antimicrobial mode of action of fusaric acid and other alkylpicolinic acid derivatives is not thoroughly understood. Therefore, we investigated their effect on cellular respiration by measuring the oxygen consumption rate of the hyphae and their impact on cell membrane integrity by determining the electrical conductivity of the mycelium. Fusaric and 9,10-dehydrofusaric acids inhibited the respiration of the mycelium and altered the permeability of the cell membrane in the tested phytopathogenic microorganisms in a concentration and exposure time-dependent manner, exerting a greater effect on oomycetes. The disruption of cell membrane integrity resulted in the leakage of cytoplasmic electrolytes into the extracellular medium, which, coupled with respiratory inhibition, could lead to cell death.

Conclusions: Fusaric and 9,10-dehydrofusaric acids show potential for the development of new fungicides and anti-oomycetes agents.

Aims: To investigate the effects of simvastatin as an antimicrobial, considering its influence on the mevalonate pathway and the bacterial cell wall of S. aureus.

Methods and results: S. aureus ATCC 29213 and 33591 were exposed to simvastatin in the presence of exogenous mevalonate to determine whether mevalonate could reverse the inhibition. S. aureus was also treated with simvastatin and gene expression analysis assays were performed to evaluate genes associated with the mevalonate pathway (mvaA, mvaS, mvaK1, and mvaK2), peptidoglycan synthesis (uppS, uppP, and murG), and cell wall stress (vraX, sgtB, and tcaA). Transmission electron microscopy was used to identify the presence of morphological changes. The data were compared using two-way ANOVA and Bonferroni post-test, or the Mann-Whitney test. Addition of exogenous mevalonate was able to partially or completely reverse the inhibition caused by simvastatin. A significant increase of the vraX gene and a reduction of the mvaA gene were observed, together with changes in bacterial morphology.

Conclusion: Simvastatin can exert its antimicrobial effect by means of changes in the cell wall associated with the mevalonate pathway.

Expansion of the microbial drug discovery pipeline has been impeded by a limited and skewed appreciation of the microbial world and its full chemical capabilities and by an inability to induce silent biosynthetic gene clusters (BGCs). Typically, these silent genes are not expressed under standard laboratory conditions, instead requiring particular interventions to activate them. Genetic, physical, and chemical strategies have been employed to trigger these BGCs, and some have resulted in the induction of novel secondary metabolites. This review encompasses a wide range of literature and emphasizes selected successful induction of microbial secondary metabolites examples through unconventional approaches such as quorum sensing, epigenetic modulation, and ribosome engineering. Whenever applicable, we will also discuss their mechanisms and optimizations to improve the microbial drug discovery process.

Aims: In this study, we report the use of two novel lytic polyvalent phages as a cocktail in in planta assays and their efficacy in the control of bacterial halo blight (BHB) caused by Pseudomonas coronafaciens pv. garcae (Pcg) in coffee plants.

Methods and results: Phages were isolated from samples of coffee plant leaves collected at two different locations in Brazil. Both phages belong to the class Caudoviricetes and present myovirus-like morphotypes, and both exhibited specificity to their host, Pcg strain IBSBF-158. The two phages were encapsulated in chitosan-coated Ca-alginate nanoparticles, which demonstrated promising performance, promoting reductions in disease severity ranging from 66.83% to 83.37%, depending on the timing of application relative to infection. Both phages were somewhat susceptible to the effects of abiotic factors when in free form, with solar radiation seriously negatively impacting their lytic activity. However, nanoencapsulation of both phages as a lytic cocktail within chitosan-coated Ca-alginate nanoparticles proved successful in fully stabilizing both phages from the deleterious action of UV radiation.

Conclusions: Application of such lytic nanoparticles in pre- and post-inoculated coffee seedlings in in planta greenhouse assays proved successful in controlling the phytopathogen responsible for BHB of coffee, Pcg, with a significant decrease in the progression of the disease. The results suggest that lytic nanoparticles may become an effective and sustainable strategy for coffee BHB control, as an alternative to conventional approaches relying on chemical (copper hydroxide or oxychloride or kasugamycin hydrochloride) or biological agents, but more studies are needed in the field to confirm this. The phage protection system developed represents a potential alternative treatment for bacterial plant diseases with minimum damage to the environment.

Aims: The present study aims to investigate the in vitro antifungal activity and mechanism of action of bamemacrolactine C (BAC), a new 24-membered macrolide compound, against Talaromyces marneffei.

Methods and results: The test drug BAC initially demonstrated antifungal activity through a paper disk diffusion assay, followed by determination of the minimum inhibitory concentration value of 35.29 μg ml-1 using microdilution. The association study revealed that combination therapy exhibited additive effects (0.5 < FICI < 1.0) when combined BAC with either amphotericin B or fluconazole. A time-growth assay confirmed that treatment with 35.29 μg ml-1 of BAC completely inhibited the growth of T. marneffei and exhibited antifungal effects. Micromorphological analysis using scanning electron microscopy and transmission electron microscopy photomicrographs revealed that BAC treatment induced morphological damage in fungal cells compared to the control group. Transmembrane protein assays showed a significant reduction in the levels of Na+/K+-ATPase (P < .05) and Ca2+-ATPase (P < .01) compared to the control group. Intracellular enzyme assays demonstrated that BAC treatment significantly decreased ATP, malate dehydrogenase, and succinate dehydrogenase content (P < .01). The combination of proteomics and parallel reaction monitoring (PRM) verification indicated that BAC exhibits an antifungal mechanism against T. marneffei by downregulating ATP citric acid lyase (ACLY) levels , potentially affecting the tricarboxylic acid (TCA) cycle. Besides, the binding model of BAC and the ACLY also shows a good docking score.

Conclusions: The findings suggest that BAC exhibits antifungal activity against T. marneffei, elucidating its multifaceted mechanism of action involving disruption of cell membranes' integrity and inhibition of intracellular enzyme activities, in which the modulation of ACLY in the TCA cycle may play an important role.

Aims: Glutamate wastewater poses a great environmental challenge to the monosodium glutamate production industry. However, its treatment solution is rich in crude protein, which has the potential to be developed as a new protein source for animal feed.

Methods and results: Given that the fermentation process generates functionally different metabolites, this study innovatively utilized two strains of feed microorganisms, Aspergillus niger and Candida tropicalis, to perform solid-state fermentation of glutamate wastewater treatment solution. The aim was to investigate and analyse the metabolite profiles during fermentation. The significant differences in metabolite profiles between the samples were determined using correlation analysis, principal component analysis, orthogonal partial least-squares discriminant analysis, variable importance in projection analysis, Kyoto Encyclopaedia of Genomes, and Human Metabolome Data Bank analysis. These variations were mainly manifested in essential feed components, such as amino acids, peptides, and their analogues. These included Ile-Pro-Asn, Pro-Gly-Val, alanylvaline, histidylisoleucine, Lys-Leu-Tyr, Ile-Arg, glycyl-leucine, leucyl-lysine, N-palmitoyl histidine, alanylisoleucine, l-glutamate, N-methylisoleucine, Isoleucylproline, dl-m-tyrosine, Isoleucyl-threonine, phenylalanine amide, carboxyethyllysine, N6-acetyl-l-lysine, citrulline, N-alpha-acetyl-l-lysine, N(6)-methyllysine, and l-aspartate-semialdehyde.

Conclusions: This study investigates the metabolite profiles of glutamate wastewater treatment solutions after co-fermentation with A. niger and C. tropicalis using solid-state fermentation. These findings provide a new strategy for efficiently utilizing glutamate wastewater treatment solutions.

Aims: UV-C based air cleaners may reduce the transmission of infectious diseases. However, microbiological validation is necessary to quantify their efficiency. In this study, the stability of aerosolized bacteriophages for validation purposes was investigated in a test room, before a UV-C based air cleaner was exemplarily evaluated regarding the inactivation of airborne bacteriophages.

Methods and results: The bacteriophage Phi6 was selected as virus surrogate and aerosolized in a room of 30 m³ volume. The recovery of infectious bacteriophages was first analyzed under variation of the relative humidity (20%-55% RH) and sampling time. The aerosol studies showed that a low humidity between 20% RH and 30% RH provides a high and stable recovery of bacteriophages Phi6 over 1 h. However, with increasing humidity, the number of infectious airborne bacteriophages Phi6 decreased significantly. At 50% RH, the recovery of Phi6 was 4 orders of magnitude lower compared to 20% RH. The validation of a UV-C based air cleaner was then demonstrated in the test room whereat the decline of infectious airborne bacteriophages was recorded over time. The nonenveloped bacteriophage MS2 was used as a reference. The validation results were significantly different for Phi6 when the humidity in the test room was either 40% RH or 30% RH, whereas comparable results were obtained for MS2 at both humidities.

Conclusion: A rising humidity in the test room caused a significant decline in the recovery of infectious airborne bacteriophages Phi6. The result of a quantitative validation of UV-C based air cleaners may therefore be affected by the respective humidity.

Aims: Determine efficacy of an aqueous photocatalytic disinfection system, photoClO2, against two human norovirus surrogates [feline calicivirus (FCV) and Tulane virus (TuV)] and Clostridioides difficile endospores on stainless steel and nylon carpet.

Methods and results: The photoClO2 system was first optimized with 1% sodium chlorite (NaClO2) and 10 ppm Eosin Y to produce 60.64 ppm ClO2/min in a 4.5 × 4.5 cm2 area. It was then tested against FCV, TuV, and C. difficile endospores on stainless steel and nylon carpet with two different backings. On stainless steel, photoClO2 achieved a > 5 log10 plaque-forming unit (PFU) reduction of FCV in 45 min, >3 log10 median tissue culture infectious dose (TCID50) reduction of TuV in 60 min, and 1.3 log10 colony-forming unit (CFU) reduction of C. difficile endospores in 120 min. Under indoor lighting conditions, photoClO2 achieved a 4.3 log10 PFU reduction of FCV and 1.4 log10 TCID50 reduction of TuV on stainless steel after 120 min. Further, photoClO2 achieved a 2.9 log10 PFU reduction of FCV and 2.5 log10 TCID50 reduction of TuV on nylon carpet with waterproof backing in 60 min, which was higher than carpet with water-permeable backing (1.3 log10 PFU and 1.1 log10 TCID50 reduction, respectively).

Conclusion: ClO2 production rate of the photoClO2 system was influenced by light distribution, while disinfection efficacy was affected by light intensity, surface characteristics, and target microorganisms. PhotoClO2 was efficacious in inactivating both human norovirus surrogates on stainless steel and nylon carpet. Efficacy against C. difficile endospores was limited.