Letters in Applied Microbiology最新文献

Based on the biodegradation of Welan gum, this paper studies the properties of Welan gum degrading enzymes, degradation rules, and the application of Welan gum oligosaccharides. In order to study the biodegradation of Welan gum, a strain W2-3 capable of degrading Welan gum, was isolated from soil and identified as Paenibacillus sp. The properties of Welan gum degrading enzymes, degradation rules, and the application of Welan gum oligosaccharides were studied. After degradation, the average molecular weight of Welan gum oligosaccharides could be degraded to 500 Da, and the molecular weight distribution range was wide. Through the hydroponic culture of barley seedlings, it was proved that the degradation products of Welan gum had a positive effect on plant growth. The results showed that Welan gum oligosaccharides could significantly increase the root length, plant height, and fresh weight of barley, and could be used as a growth regulator in agricultural production.

Widely regarded as a so-called "superfood," microgreens have become an increasingly significant food crop from both nutritional and agricultural standpoints. However, similar to other produce commodities that are also cultivated using modernized indoor farming methods, there have been mounting concerns over the potential risks of consuming microgreens contaminated by Listeria monocytogenes. To gain insights into the microbial properties of microgreens, this study characterized the bacterial composition of fresh microgreen retail products using amplicon sequencing of 16S rRNA genes. Dominated by Gammaproteobacteria, a total of 36 shared genera were identified as putative constituents of the microgreen core microbiome. By monitoring the dynamics of microgreen-borne bacteria undergoing a Listeria-selective cultural enrichment procedure, it was revealed that, regardless of the presence or absence of L. monocytogenes, off-target bacteria of the Klebsiella and Enterococcus genera were significantly enriched from microgreens by the primary enrichment step, with the secondary enrichment step continuing to promote the expansion of Enterococcus population. While Listeria was generally neither the most-enriched nor the dominant taxon in cultures sampled at different enrichment stages, significant enrichment of Lysinibacillus and Bacillus bacteria was detected in microgreens contaminated with L. monocytogenes, suggesting they could be co-enriched in competition with Listeria.

In fermented plant foods, phenolic compounds are metabolized by 2-ene reductases, which reduce double bonds adjacent to an aromatic rings in phytochemicals, including hydroxycinnamic acids, isoflavones, and flavones. Only few 2-ene reductases of lactic acid bacteria were characterized, including the hydrocinnamic reductases HcrB and Par1, and the daidzein reductase of Lactococcus lactis. This study aimed to characterize HcrF, a homologue of HcrB, in Limosilactobacillus fermentum. HcrF was purified after cloning in Escherichia coli and purification by affinity chromatography. HcrF was optimally active at 30°C-40°C and pH 7.0 and required both flavin mononucleotide and nicotinamide adenine dinucleotide as co-factors. Ferulic, caffeic, p-coumaric, and sinapic acids but not trans-cinnamic acids were reduced to dihydro derivatives. The maximum reaction velocity Vmax of HcrF was highest for ferulic acid. On a phylogenetic tree of 2-ene reductases, HcrF clustered most closely with the hydroxycinnamic acid reductase HcrB of Lactiplantibacillus plantarum. The hydroxycinnamic acid reductase Par1 of Furfurilactobacillus milii and flavone or isoflavone reductases were only distantly related to HcrF. In summary, current knowledge does not allow to predict the substrate specificity of 2-ene reductases on the basis of the protein sequence; this study adds HcrF to the short list of enzymes with known substrate specificity.

In the present study, nutraceutical citrulline was produced using immobilization of permeabilized whole cells of Pseudomonas furukawaii, an efficient producer of ADI. Since arginine deiminase (ADI) is intracellularly localized, various additives such as SDS (Sodium dodecyl sulfate), Triton X-100, and EDTA (Ethylenediaminetetraacetic Acid) were used to permeabilize the cell to improve substrate accessibility and ADI activity. The maximum ADI activity was observed with 0.25 mg ml-1 biomass concentration treated with 0.5 mmol l-1 EDTA for 15 min using OFAT (One factor at a time) approach. Optimization of permeabilization conditions of P. furukawaii cells using novel neural networks and particle swarm optimization led to maximum ADI activity with 0.10 mmol l-1 EDTA and 0.30 mg ml-1 biomass. Further, the morphological characterization of immobilized cells was assessed by field emission scanning electron microscopy and FTIR (Fourier transform infrared spectroscopy). An optimal citrulline production of 1.19 mmol l-1 was achieved at 2.5% sodium alginate with 20 mmol l-1 arginine at 38°C, and 180 min of incubation. The immobilized cells retained 90.3% productivity after seven reuse cycles. Thus, the formulated immobilized whole-cell biocatalyst, with higher stability offers cost-effective methods of citrulline production.

In response to the World Health Organization's research agenda of antimicrobial resistance in human health, this study appraised the antibacterial and antibiofilm synergistic activity of meropenem and ZnO nanoparticles (ZnO-NPs) combination against carbapenem-resistant Klebsiella pneumoniae (CRKP). The minimum inhibitory concentration (MIC) of meropenem in combination was found to be ~1/12 of its MIC alone. The results of microtiter dilution assay showed that the combination was more efficient in reducing the biofilm biomass than meropenem alone or ZnO-NPs alone. The scanning-electron-microscopy micrographs elucidated that the combination of meropenem with ZnO-NPs has significantly enhanced its competence in eradicating the preformed biofilms of CRKP strains. In addition, the relative gene expression results showed that the combination compared to the meropenem alone and ZnO-NPs alone eloquently down-regulated the expression of biofilm genes (mrkA, fimA, and ecpA). Besides, the MTT-assay demonstrated that the combination has limited cytotoxicity against Vero-cells (in vitro). Overall, this study represents an efficient safe enhancement of meropenem to tackle the growing health threat of CRKP and carbapenem-resistant Enterobacterals prevalence.

During pig slaughter, contaminants such as intestinal and stomach contents, bile, tubular rail fat, and reddish foam from the respiratory tract frequently appear on carcasses, potentially compromising meat safety. This study examined the impact of these contaminants on the bacterial loads of pig carcasses, using total bacterial counts and Enterobacteriaceae counts as hygiene indicators. Examination of the substances as such showed that intestinal and stomach contents were particularly conspicuous to undermine the carcase hygiene due to total bacterial counts of ∼6.0 log10 CFU g-1 (intestinal content) and 5.5 log10 CFU g-1 (stomach content). Tubular rail fat showed varying contamination levels, from low (3.1 log10 CFU g-1) to high (6.4 log10 CFU g-1). The reddish foam had moderate contamination (4.3 log10 CFU g-1). Enterobacteriaceae levels mirrored these results at a lower level. Subsequently, a comparative study analysing bacterial levels in contaminated and in noncontaminated pork rind regions was performed. Even small amounts of intestinal and stomach contents led to significant increases in total bacterial counts of up to 3 log10 CFU cm-² and in Enterobacteriaceae counts (up to 5 log10 CFU cm-²). Other contaminants did not significantly raise bacterial levels: their total viable counts around 3.5 log10 CFU cm-² were similar to those of uncontaminated carcass areas. Nevertheless, they should be removed before further processing.

Escherichia coli Nissle 1917 (EcN) is a unique probiotic utilized to treat inflammatory bowel disease and irritable bowel syndrome. Outer membrane vesicles (OMVs) from EcN can not only deliver pro-biotic anti-inflammatory molecules to cancer cells to exert anti-rectal cancer effects, but also deliver therapeutic drugs, genes, and other "cargoes" encapsulated in the vesicles to specific cells, making them an ideal vehicle for drug delivery. In this study, we successfully isolated OMVs of probiotic origin and obtained BCN-OMVs by encapsulating baicalin (BCN) in EcN-OMVs. Fluorescence microscopy showed that both fluorescently labeled EcN-OMVs and BCN-OMVs were able to enter HT-29 cells. The results of CCK-8, plate cloning, flow cytometry, and western blotting indicated that the vitality and proliferation of HT-29 cells were sensibly inhibited after treatment with BCN-OMVs. Additionally, apoptosis-related proteins and proteins involved in the NF-κB pathway were also expressed differently. The results above suggest that EcN-OMVs, serving as a bio-nanocarrier of BCN, can effectively address the limitations of BCN, such as poor water solubility and low bioavailability. They also play a significant anti-tumor role by enhancing cancer cell apoptosis, showing promising potential in targeted therapy for colorectal cancer (CRC).

Crop residue management is vital in the rice-wheat cropping system, influencing soil health and crop productivity. This study examined the effects of organic and inorganic fertilizers and microbial decomposers on rice growth and yield. We evaluated seven treatments: 100% recommended dose fertilizer (RDF); 50% residue + 50% RDF; 50% residue + 50% RDF + Pusa decomposer; 50% residue + 50% green manuring (GM)/green leaf manuring (GLM); 50% residue + 50% GM/GLM + Pusa decomposer; residue @ 2.5 tons per acre + Pusa decomposer; residue @ 2.5 tons per acre + no Pusa decomposer; and absolute control. Results indicate that integrating organic and inorganic fertilizers with microbial decomposers positively affects rice growth and yield parameters. While adding microbial decomposer to RDF did not consistently enhance rice yield, it improved soil enzymatic properties. This suggests that the effectiveness of microbial decomposers may vary based on specific soil and crop conditions. Therefore, microbial decomposers present a promising approach to boost soil health and fertility. Further research is needed to optimize conditions for their use and systematically assess their impact on crop yields.

Precise and timely diagnosis is essential to prevent severe outcomes of leptospirosis in humans and animals. Existing diagnostic methods face challenges and limitations, underscoring the need for novel, field-applicable screening, and diagnostic tests/assays. This study evaluates the diagnostic utility of a recombinant ErpY-like lipoprotein (rErpY-LIC11966) in a latex agglutination test (LAT) for diagnosis of animal leptospirosis. The ErpY gene sequence from Leptospira interrogans serovar Pomona, excluding the signal peptide, was amplified, cloned into the pETite vector, and expressed in Escherichia coli. The expressed rErpY (∼16 kDa) was characterized by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis and Western blot using Leptospira-specific standard sera. To assess the diagnostic potential of rErpY, Ni-NTA affinity-purified protein was used to sensitize latex-coated beads (0.8 µm colour beads), which were then employed in the LAT for standardization and optimization with standard positive and negative sera. For evaluation, the rErpY-LAT was tested on serum samples from 177 suspected animal cases and compared to the microscopic agglutination test. It showed a relative diagnostic sensitivity of 90.6%, a specificity of 89.1%, and an overall accuracy of 90%. This study proposes rErpY-LAT as a field testing/screening diagnostic tool for preliminary serodiagnosis of leptospirosis, highlighting the potential of recombinant protein-based assays to address current diagnostic challenges.

Minas Frescal cheese (MFC) is a perishable product with high water activity and neutral pH, conditions that favor the development of microorganisms. Total aerobic bacteria (TAB) can deteriorate the cheese, negatively affecting its sensory characteristics. By controlling TAB, the shelf life of the product is extended and its quality is maintained, contributing to meeting consumer expectations. This study aimed to evaluate the individual and combined effect of technological treatments of high hydrostatic pressure (HHP) and ultraviolet C radiation (UV-C) on the TAB count present in the natural microbiota of MFC, as an alternative to control the microbiological quality of this product. After production, MFC were subjected to treatments with different levels of HHP (100-400 MPa/10 min) and UV-C (0.097-0.392 J/cm2 s-1). The combinations of HHP and UV-C doses were determined by a central composite rotational design. The model efficiently described the individual and combined effect of HHP and UV-C on TAB, demonstrating that gradually increasing HHP levels reduces TAB counts in MFC, regardless of the UV-C dose applied. This study contributes significantly to the literature by providing new insights into how these technologies can be used to improve the microbiological quality of fresh cheeses.