Journal of Applied Microbiology最新文献

Aims: The aim of this study was to evaluate the impact of the introduction of a phosphoribosylpyrophosphate synthetase (PRS) mutation into a plant growth-promoting strain of Methylorubrum on the enhancement of phyllosphere colonization, with the ultimate goal of improving plant growth and quality.

Methods and results: A strain of Methylorubrum populi (named HS04) was isolated from the groundnut leaves and found to process the plant-promoting traits, including the ability to produce indole acetic acid, siderophore, 1-aminocyclopropane-1-carboxylate deaminase, and to fix nitrogen. The application via foliar spray significantly increased the fresh weight of cucumber seedlings cultivated in a standard growth chamber, with 43.0% higher than the control group. Genomic analysis revealed that the presence of an array of genes involved in plant growth promotion, including accD, aldB, and ltaE, as well as potential nitrogen-fixation-related genes, including nifA, bchlLNB, and bchXYZ, in the HS04 strain. The introduction of the PRS mutation (an aspartic acid to an asparagine residue, D38N) in the HS04 strain (named HS04PTR) enhanced the utilization capacity of low concentrations of methanol and multi-carbon sources (C2-C5 carbon sources). The HS04PTR strain indicated a notable enhancement in the phyllosphere colonization, with the subsequent application further promoting the growth of cucumber seedlings. An agricultural solar greenhouse experiment was thus performed to assess the efficiency of the HS04PTR strain, sprayed at low abundance, in improving the growth and quality of cucumber plants, including vitamin C, reducing sugars, and total sugars.

Conclusions: Our findings provide insights into the potential of Methylorubrum/Methylobacterium strains with the PRS mutations as an efficient inoculant for advantageous agricultural applications.

Aims: This study aimed to evaluate the potential of phage phSE-5 to inactivate Salmonella enterica serovar Typhimurium in milk (at 4, 10, and 25°C), liquid whole egg, and eggshell (at 25°C for both matrices).

Methods and results: Since the success of phage treatment in food depends on maintaining phage viability towards different food conditions, firstly the stability of phage phSE-5 at different temperatures and pHs was assessed. The effect of phage phSE-5 against S. Typhimurium was then assessed in vitro (liquid culture medium-TSB) and finally in the selected food matrices. Phage phSE-5 was stable for long storage periods (56 days) at pH 7-8 and 4-25°C. At 25°C, the efficacy of phage phSE-5 was matrix-dependent with differences in the sample, relatively to the bacterial control, of 2.7, 4.6, 1.8, and 1.3 log colony-forming units (CFU) ml-1 in TSB, milk, liquid whole egg, and eggshell, respectively. Also, phage phSE-5 led to reductions relatively to the initial bacterial concentration only in TSB and milk with 1.9 and 2.1 log CFU ml-1 reduction, respectively. Additionally, this phage was more efficient at 25°C in the tested matrices than at 10°C (no reduction and 1.7 log CFU ml-1 reduction in TSB and milk, respectively; maximum difference of 1.7 and 3.3 log CFU ml-1 in TSB and milk, respectively) and 4°C (no bacterial reduction/difference was observed in both TSB and milk). However, the decrease in temperature from 25 to 10°C slowed down bacterial regrowth after phage treatment.

Conclusions: Our results show that phages are promising and environmentally friendly candidates for use as biocontrol agents against S. Typhimurium in milk, liquid whole egg, and eggshell, allowing a reduction in energy costs if carried out at 10°C.

Antimicrobial resistance (AMR), arising from decades of imprudent anthropogenic use of antimicrobials in healthcare and agriculture, is considered one of the greatest One Health crises facing healthcare globally. Antimicrobial pollutants released from human-associated sources are intensifying resistance evolution in the environment. Due to various ecological factors, wildlife interact with these polluted ecosystems, acquiring resistant bacteria and genes. Although wildlife are recognized reservoirs and disseminators of AMR in the environment, current AMR surveillance systems still primarily focus on clinical and agricultural settings, neglecting this environmental dimension. Wildlife can serve as valuable sentinels of AMR in the environment, reflecting ecosystem health, and the effectiveness of mitigation strategies. This review explores knowledge gaps surrounding the ecological factors influencing AMR acquisition and dissemination in wildlife, and highlights limitations in current surveillance systems and policy instruments that do not sufficiently address the environmental component of AMR. We discuss the underutilized opportunity of using wildlife as sentinel species in a holistic, One Health-centred AMR surveillance system. By better integrating wildlife into systematic AMR surveillance and policy, and leveraging advances in high-throughput technologies, we can track and predict resistance evolution, assess the ecological impacts, and better understand the complex dynamics of environmental transmission of AMR across ecosystems.

Aims: Flavobacterium strains are widely distributed in various environments and generally exhibit specialized roles in the degradation of complex organic substrates. To obtain a deeper understanding of their enzyme profiles, patterns of action on natural carbohydrates degradation, and to mine gene resources for biomass conversion.

Methods and results: We sequenced the whole genome of a novel carbohydrate-degrading Flavobacterium sp. strain YJ01. The genome size of strain YJ01 was 5.48 Mb and encoded 4674 predicted genes. Comparative genomic analysis revealed Flavobacterium strains were characterized by the presence of abundant genes associated with catalytic activity and metabolic processes, especially carbohydrate metabolism. About 9% of genes of strain YJ01 encoded carbohydrate-active enzymes. These enzymes can act on various complex natural and cellular carbohydrates. The synergistic effect of the enzymes on the hydrolysis of complex natural polysaccharides was further experimentally evidenced by using starch and xylan as substrates, in which the degradation rate of an enzyme combination was ~10-fold higher than that of the single enzyme.

Conclusions: Flavobacterium sp. strain YJ01 has a high degree of catalytic and metabolic activity toward carbohydrates, and it harbors abundant, complete, and efficient enzymes for mediating complex polysaccharide degradation. These enzymes, acting synergistically on complex substrates, greatly improved the efficiency of digestion, which may be associated with the extensive ecological adaptability of Flavobacterium, which genetically heterologous divergent from extremely environments origin Flavobacterium strains.

Aim: Bacillus subtilis is usually found in soil, and their biocontrol and plant growth-promoting capabilities are being explored more recently than ever. However, knowledge about metabolite production and genome composition of endophytic B. subtilis from seeds is limited. In the present study, B. subtilis EVCu15 strain isolated from the seeds of Vasconcellea cundinamarcensis (mountain papaya) was subjected to whole genome sequencing and detailed molecular and functional characterization.

Methods and results: Whole genome sequencing and sequence analysis of the endophytic bacterium from mountain papaya seed revealed that the bacterium was B. subtilis, strain EVCu15. The genomic sequence had more than 98% nucleotide similarity with two published whole genome sequences of B. subtilis strains. Some of the important secondary metabolite gene clusters involved in production of bioactive compounds such as surfactin, fengycin, plipastatin, bacillibactin, bacillaene, subtilomycin, subtilosin A, and bacilysin were identified from the whole genome sequence analysis. Genes encoding several plant growth-promoting metabolites, mostly involved in the nutrient metabolism, were identified in the bacterial genome. These included factors coding for nitrogen, phosphorus, iron, sulfur, potassium, and trehalose metabolism. Genes involved in auxin, riboflavin, acetoin biosynthesis, ACC deaminase activity, and xylan degradation were also identified. Proteomic analysis confirmed the biosynthesis and release of several bioactive secondary metabolites in the endophytic B. subtilis strain EVCu15. Liquid chromatography-mass spectrometry-based profiling for hormones and vitamins identified extracellular secretion of several important plant growth-promoting compounds such as IAA, salicylic acid, zeatin, vitamin D1, D2, E, K1, and pyridoxine. The in vitro and in vivo studies with the endophytic B. subtilis against various plant pathogenic fungi showed moderate to high levels of resistance. The B. subtilis EVCu15 compared to B. amyloliquefaciens showed better control over the root-knot nematode Meloidogyne incognita, in terms of egg hatching inhibition and the mortality of J2 juveniles.

Conclusion: Overall, this study underscores the biocontrol and plant growth-promoting potential of B. subtilis EVCu15, an endophyte isolated from mountain papaya seeds. Genomic analysis revealed a significant proportion of genes linked to biocontrol and plant growth promotion, corroborating its efficacy against M. incognita and various plant pathogens in vitro and in greenhouse studies. Furthermore, the bacterium's ability to produce diverse bioactive compounds, including proteins, hormones, and vitamins, was confirmed, highlighting its complex interactions within the plant system.

Aims: Enterococcus faecium is one of the most important opportunistic pathogens threatening human health worldwide. Resistance to vancomycin (VAN) is increasing at an alarming rate. Resurrecting antibiotics using a combination approach is a promising alternative avenue. Galangin (GAL) is a bioactive compound constituted in herbal plants. This study aimed to evaluate the synergistic activity of the combination of GAL and VAN and mode of action against vancomycin-resistant E. faecium (VREfm) strains.

Methods and results: The minimal inhibitory concentrations against these bacteria were 8-64 μg ml-1 for VAN and 512 μg ml-1 for GAL. The VAN plus GAL combination exhibited synergistic effects against E. faecium isolates, with a fraction inhibitory concentration index of 0.26-0.28. Time-kill assays confirmed this synergism. Mechanistic studies showed that the combination induced intracellular constituent leakage, suggesting impaired membrane permeability and electron microscopy revealed peptidoglycan and membrane damage. Additionally, the GAL plus VAN combination inhibited biofilm formation and significantly reduced lipid, protein, and carbohydrate contents, as shown by Fourier-transform infrared spectroscopy (FTIR).

Conclusions: GAL could reverse the activity of VAN against VREfm by damaging bacterial cell envelope, inhibiting biofilm formation, and reducing biomolecule contents, emphasizing its potential as a valuable adjunct to VAN in treating VREfm infections.

Aims: To isolate polyethylene terephthalate (PET)-degrading bacteria and elucidate the underlying mechanisms of PET biodegradation through biochemical and genome analysis.

Methods and results: Rhodococcus rhodochrous IITR131 was found to degrade PET. Strain IITR131 genome revealed metabolic versatility of the bacterium and had the ability to form biofilm on PET sheet, resulting in the cracks, abrasions, and degradation. IITR131 showed a reduction of 19.7%, exhibiting a half-life of 189.9 d of 0.1 mm PET film in 60 d and formed metabolites bis(2-hydroxyethyl) terephthalate (BHET), terephthalic acid (TPA), and benzoic acid (BA). The draft genome of 5.9 Mb of IITR131 revealed that this bacterium has plethora of genes such as terephthalate 1, 2 dioxygenase, carboxylesterase that together constituted a complete pathway for PET degradation. Moreover, strain IITR131 was found to have a variety of genes encoding for enzymes for the metabolism of several plastic polymers, xenobiotics including chloroalkanes, and polycyclic aromatic hydrocarbons.

Conclusions: Rhodococcus rhodochrous IITR131 demonstrated a significant potential in the biodegradation of PET. The comprehensive genomic and metabolic analyses further elucidated the molecular pathway involved in PET degradation, enhancing our understanding of the mechanisms underlying microbial PET biodegradation. These findings underscore the applicability of R. rhodochrous IITR131 in biotechnological approaches for mitigating plastic pollution.

Aims: To investigate the effects of Lactococcus lactis subsp. lactis strains LL100933 and LL12007 on the host defense mechanisms of Caenorhabditis elegans against pathogenic infections and stressors.

Methods and results: Caenorhabditis elegans fed a 1:1 mixture of Escherichia coli OP50 and LL100933 (OP50 + LL100933) or E. coli OP50 and LL12007 (OP50 + LL12007) had significantly higher survivability than the control diet (OP50). Moreover, when OP50 + LL100933 and OP50 + LL12007 were fed to C. elegans deficient in daf-16 and pmk-1, survival did not exceed that of control-fed worms under Salmonella infection. Therefore, these strains may enhance the survivability of C. elegans through the p38 MAPK and DAF-16-related pathways. Gene expressions responsible for these enhanced defense responses were estimated using RNA sequencing and gene ontology analysis. The test groups showed significant upregulation of glutathione S-transferase (gsto-1, gst-5, and gst-17), UDP-glucuronyl transferase (ugt-13, ugt-16, and ugt-21), heme-responsive (hrg-4), invertebrate-type lysozyme (ilys-2), and C-type lectin (clec-52) genes compared to those in the control group.

Conclusion: Lactococcus lactis subsp. lactis LL100933 and LL12007 strains demonstrated promising benefits as probiotics for enhancing host defense mechanisms in C. elegans.

Aim: Aeromonas spp. are common members of water and wastewater microbiomes, but some are listed as opportunistic pathogens and are often reported to carry antimicrobial resistance (AMR) genes. We aimed to assess the performance of isolation media for capturing their distribution and their role in AMR dissemination into aquatic environments.

Methods and results: We investigated the abundance, diversity, and AMR profile of Aeromonas isolates from wastewater and receiving water bodies at five municipal wastewater treatment plants in Denmark using three isolation media. This was then compared with the diversity estimated from community-wide 16S rRNA gene amplicon sequencing and resistance patterns inferred from high-throughput qPCR of resistance genes. Isolates from ampicillin sheep blood agar were the most phylogenetically diverse, but the overall Aeromonas recovery on the three media was similarly good and matched the dominant amplicon sequence variants. While the dominant phylotypes were ubiquitous, some types were only detected in treated wastewater and the receiving rivers. The resistance prevalence was moderate and mostly to beta-lactams and tetracyclines. Isolates resistant to piperacilin-tazobactam, cefepime, and tetracycline downstream of the plants were linked to wastewater origin.

Conclusion: Overall, our work demonstrates Aeromonas and Aeromonas-mediated AMR fluxes at the wastewater/environment interfaces and provides methodological bases for monitoring aeromonads in wastewater and surface waters.

Aims: Disulfiram (Antabuse®) is an oral alcohol sobriety medication that exhibits antimicrobial activity against Gram-positive facultative anaerobes. The aims of this study were to measure the antimicrobial activity against anaerobic bacteria of the gut human microbiome and establish the extent that disulfiram alters the microbial composition of the ileum, cecum, and feces using C57BL/6 mice.

Methods and results: Antimicrobial susceptibility testing by the microdilution method revealed that disulfiram inhibits the in vitro growth of gut anaerobic species of Bacteroides, Clostridium, Peptostreptococcus, and Porphyromonas. Differential sequencing of 16S rRNA isolated from the ileum, cecum, and feces contents of treated vs. untreated mice showed that disulfiram enriches the Gram-negative enteric population. In female mice, the enrichment was greatest in the ileum, whereas the feces composition in male mice was the most heavily altered.

Conclusions: Daily administration of oral disulfiram depletes the enteric Gram-positive anaerobe population as predicted by the minimum inhibitory concentration data for isolates from the human gut microbiota.