Journal of Applied Microbiology最新文献

Aims: Klebsiella michiganensis is a medically important bacterium that has been subject to relatively little attention in the literature. Interrogation of sequence data from K. michiganensis strains in our collection has revealed the presence of multiple large plasmids encoding type II toxin-antitoxin (TA) systems. Such TA systems are responsible for mediating a range of phenotypes, including plasmid stability ('addiction') and antibiotic persistence. In this work, we characterize the hipBA TA locus found within the Klebsiella oxytoca species complex (KoSC).

Methods and results: The HipBA TA system is encoded on a plasmid carried by K. michiganensis PS_Koxy4, isolated from an infection outbreak. Employing viability and plasmid stability assays, we demonstrate that PS_Koxy4 HipA is a potent antibacterial toxin and that HipBA is a functional TA module contributing substantially to plasmid maintenance. Further, we provide in silico data comparing HipBA modules across the entire KoSC.

Conclusions: We provide the first evidence of the role of a plasmid-encoded HipBA system in stability of mobile genetic elements and analyse the presence of HipBA across the KoSC. These results expand our knowledge of both a common enterobacterial TA system and a highly medically relevant group of bacteria.

Aim: Fire blight, attributed to the bacterium Erwinia amylovora, significantly damages economically important crops, such as apples and pears. Conventional methods for managing fire blight involve the application of chemical pesticides, such as streptomycin and oxytetracycline. Nevertheless, apprehensions are increasing regarding developing antibiotic and pesticide-resistant strains, compounded by documented instances of plant toxicity. Here, we present that Streptomyces recifensis SN1E1 has exhibited remarkable efficacy in suppressing apple fire blight disease. This study aims to unravel the molecular-level antimicrobial mechanisms employed by the SN1E1 strain.

Methods and results: We identified four antimicrobial-associated biosynthetic gene clusters within the genomics of S. recifensis SN1E1. To validate antimicrobial activity against E. amylovora, knock-out mutants of biosynthetic genes linked to antimicrobial activity were generated using the CRISPR/Cas9 mutagenesis system. Notably, the whiE4 and phzB deficient mutants displayed statistically reduced antibacterial activity against E. amylovora.

Conclusion: This research establishes a foundation for environmental and biological control studies. The potential utilization of environmentally friendly microbial agents derived from the SN1E1 strain holds promise for the biological control of fire blight disease.

Aim: To investigate the effect of pyruvate and glucose on leucine transamination and 3-methylbutanal production by Lactococcus lactis, including the comparison with cells possessing glutamate dehydrogenase (GDH) activity.

Methods and results: Lactococcus lactis cells were incubated in chemically defined medium (CDM) with the pH controlled at 5.2 to mimic cheese conditions. Pyruvate supplementation stimulated the production of the key flavour compound 3-methylbutanal by 3-4 times after 72 h of incubation. Concurrently, alanine production increased, demonstrating the involvement of pyruvate in transamination reactions. Glucose-metabolizing cells excreted α-ketoisocaproic acid and produced even 3 times more 3-methylbutanal after 24 h than pyruvate-supplemented cells. Conjugal transfer technique was used to transfer the plasmid pGdh442 carrying the gdh gene encoding for GDH to L. lactis. Introducing GDH did not stimulate the excretion of α-ketoisocaproic acid and the production of 3-methylbutanal.

Conclusions: These results demonstrate that Lactococcus uses pyruvate to transaminate leucine into α-ketoisocaproic acid which supports 3-methylbutanal production. Surprisingly, GDH activity did not stimulate leucine transamination and 3-methylbutanal production.

Aims: Antibiotic resistance genes (ARGs) in the environment pose significant public health concerns and are influenced by conditions like temperature changes. We previously observed that resistance evolution to gentamicin and colistin affects optimal growth temperatures in Staphylococcus epidermidis isolates. Despite significant phenotype observations, the genetic basis remains unclear. We aim to identify the genetic changes linked to antibiotic resistance evolution that alter optimal growth temperature.

Methods and results: Using whole-genome sequencing, we sequenced the genomes of gentamicin-resistant (GEN-1, GEN-2) and colistin-resistant (COL-4, COL-6) S. epidermidis isolates. Variant analysis with the BV-BRC bioinformatics tool identified genes involved in antibiotic resistance and temperature response. We found 12 genetic variants, including two unique to GEN-2 and one in COL-4. One shared mutation was observed in GEN-1 and GEN-2, and another in COL-4 and COL-6. Five mutations were shared among all isolates related to mobile gene elements, including a transposase IS4 family, two putative transposases, and two transposase-like insertion elements.

Conclusions: Our findings indicate that the same genes involved in gentamicin and colistin resistance, especially those related to mobile genetic elements, may also play a crucial role in temperature response.

Aims: Volatile organic compounds (VOCs) have an important function in plant growth-promoting rhizobacteria (PGPR) development and plant growth. This study aimed to identify VOCs of the PGPR strain, Stutzerimonas stutzeri NRCB010, and investigate their effects on NRCB010 biofilm formation, swarming motility, colonization, and tomato seedling growth.

Methods and results: Solid-phase microextraction and gas chromatography-mass spectrometry were performed to identify the VOCs produced during NRCB010 fermentation. A total of 28 VOCs were identified. Among them, seven (e.g. γ-valerolactone, 3-octanone, mandelic acid, 2-heptanone, methyl palmitate, S-methyl thioacetate, and 2,3-heptanedione), which smell well, are beneficial for plant, or as food additives, and without serious toxicities were selected to evaluate their effects on NRCB010 and tomato seedling growth. It was found that most of these VOCs positively influenced NRCB010 swarming motility, biofilm formation, and colonization, and the tomato seedling growth. Notably, γ-valerolactone and S-methyl thioacetate exhibited the most positive performances.

Conclusion: The seven NRCB010 VOCs, essential for PGPR and crop growth, are potential bioactive ingredients within microbial fertilizer formulations. Nevertheless, the long-term sustainability and replicability of the positive effects of these compounds across different soil and crop types, particularly under field conditions, require further investigation.

Aims: To explore the therapeutic potential of Forsythoside B in treating Streptococcus pneumoniae (S. pneumoniae) infections, focusing on its ability to inhibit pneumolysin activity and protect cells from damage.

Methods and results: Hemolysis tests were used to evaluate Forsythoside B's inhibitory effect on pneumolysin activity, while growth curve analysis assessed its impact on S. pneumoniae growth. Western blotting and oligomerization analysis were conducted to examine its influence on pneumolysin oligomerization. Cytotoxicity assays, including LDH release and live/dead cell staining, evaluated the protective effects of Forsythoside B against pneumolysin-induced damage in A549 cells. Additionally, a mouse model was employed to test the effects on survival rates, lung bacterial load, and inflammation. The results showed that Forsythoside B significantly inhibited pneumolysin activity, reduced its oligomerization, and protected A549 cells from damage without affecting bacterial growth. In the mouse model, it improved survival rates and reduced lung inflammation, indicating its potential as a therapeutic agent against S. pneumoniae infections.

Conclusions: Forsythoside B shows potential as a therapeutic agent for treating pneumonia, particularly in infections caused by S. pneumoniae.

Aims: To identify efficient, broad-spectrum, and non-toxic preservatives for natural agricultural products, eight essential oils were screened for high inhibitory and antioxidant activities against spoilage microbes.

Methods and results: The zone of inhibition test and minimum inhibitory concentration (MIC) assay were performed to assess the antimicrobial activity of eight essential oils against Bacillus subtilis, Staphylococcus aureus, Penicillium, Saccharomyces, and Escherichia coli. Among the eight essential oils, garlic and rose essential oils exhibited the best inhibitory effects, their MICs against the spoilage microbes were 40-640 μl/l and 10-320 μl/l, respectively. In addition, the antioxidant activities of eight essential oils were compared using the DPPH and ABTS radical-scavenging assays and the reducing power assay. Eight essential oils had antioxidant capacity, among which rosemary, thyme, rose, and tea tree essential oils performed the best. Moreover, the combination of thyme and rose exerted stronger antioxidant activity. Therefore, the concentrations of rose and garlic, and thyme essential oils were optimized using response surface methodology to obtain the optimal composite ratios, which were 1254 μl/l, 640 μl/l, and 1228 μl/l for rose, garlic, and thyme, respectively. The DPPH free radical-scavenging rate detected using this formulation was 50.2%, basically consistent with the prediction. Zone of inhibition diameters with the compound essential oil, against five spoilage microbes, were all greater than 45 mm.

Conclusions: The essential oil combination had high antimicrobial, against agricultural product spoilage microbes, and antioxidant activities.

Aims: Cupriavidus isolates are found in environmental and clinical samples and are often resistant to carbapenems, which are last-resort antibiotics. However, their carbapenem-resistance molecular mechanisms remain unknown. This study aimed to (i) characterize and sequence the carbapenem-resistant soil isolate Cupriavidus taiwanensis S2-1-W to uncover its antibiotic resistance determinants; and (ii) clone and characterize a putative novel carbapenemase gene identified in this isolate.

Methods and results: Antibiotic susceptibility testing of C. taiwanensis S2-1-W revealed that it was resistant to most carbapenems, other β-lactams, and aminoglycosides tested. Genome sequencing of this isolate revealed a complex chromosomal resistome that included multidrug efflux pump genes, one aminoglycoside transferase gene, and three β-lactamase genes. Among them, we identified a novel putative class D β-lactamase gene (blaOXA-1206) that is highly conserved among other sequenced C. taiwanensis isolates. Cloning and characterization of blaOXA-1206 confirmed that it encodes for a newly discovered carbapenemase (OXA-1206) that confers resistance to carbapenems and other β-lactams.

Conclusion: Carbapenem-resistance in C. taiwanensis S2-1-W is associated with a newly discovered carbapenemase, OXA-1206.

Aims: This study examined the diversity of arbuscular mycorrhizal fungi (AMF), mean spore density (MSD), and root colonization in relation to factors such as agroclimatic zones, rice varieties and soil types in paddy fields of South India. The aim was to understand how these factors influence AMF association in rice, facilitating their effective use as a biological tool in paddy cultivation.

Methods and results: AMF were identified through light microscopy of spores, while MSD and percentage-root-length colonization (PRLC) were measured using standard methods. Correlation and principal component analyses were performed to explore the interrelationships between AMF characteristics and various environmental, soil, and plant variables. Sixteen AMF species were identified across 29 rice varieties from three agroclimatic zones, 6 soil orders, and 18 soil series over 2 seasons. Notably, 70% of chemicalized rice fields lacked AMF spores, and only 50% exhibited root colonization. This study offers new insights into the role of AMF in rice cultivation.

Conclusion: The AMF diversity and root colonization in relation to environmental variables underscore their significant impact on AMF in particular crop fields.

Aims: The survival of inoculated Escherichia coli on Fuji apples in Washington State orchards was studied, considering evaporative cooling, canopy location, year, and region, with the examination of sunlight exposure and inoculation levels in year 2.

Methods and results: Rifampicin-resistant E. coli was applied to Fuji apples. Initial concentrations for the high-inoculation study were 7.4 ± 0.3 log10 CFU per apple and 3.4 ± 0.3 log10 CFU per apple for the low-inoculation study. Enumeration of E. coli was conducted at 0, 2, 10, 18, 34, 42, 58, 82, 106, and 154 h after inoculation. Results were analyzed using Tukey's honest significance difference test and a log-linear model. Log-linear, Weibull, and biphasic models characterized E. coli die-off patterns for high and low inoculations. The application of evaporative overhead cooling water did not significantly influence E. coli survival on Fuji apples; inoculation level and sunlight exposure were significant factors in a log-linear model. Escherichia coli decreased by 5.5 ± 1.3 and 3.3 ± 0.4 log10 CFU per apple for high and low-inoculated apples, respectively, by 154 h. The biphasic model best explained the die-off pattern for high and low-inoculated Fuji apples.

Conclusions: Overhead evaporative cooling, a useful fruit quality practice, did not impact the survival of generic E. coli on Fuji apple surfaces. The significant impact of sunlight exposure and inoculation levels on die-off highlights the importance of ultraviolet radiation in risk reduction and the need for various inoculum concentrations in preharvest field studies.