Journal of Applied Microbiology最新文献

Aims: Microbial communities in paddy soils act as potential sinks of nitrous oxide (N2O), a notorious greenhouse gas, but their potential to reduce external N2O is unclear. The direct observation of N2O reduction in submerged field soils is technically difficult. Here, we aimed to identify soil microbial clades that underpin the strong N2O mitigation capacity.

Methods and results: We constructed paddy soil microcosms with external N2O amendment that enabled the simultaneous evaluation of N2O reductase gene (nosZ) transcripts and N2O consumption. Although the amount of N2O amended was large, it was mostly consumed after 6-8 days of microcosm incubation. Metatranscriptomic sequencing revealed that betaproteobacterial nosZ, especially those classified as clade II nosZ belonging to the orders Rhodocyclales or Nitrosomonadales, occupied > 50% of the nosZ transcripts in three of the five paddy soils used. On the other hand, publicly available shotgun metagenomic sequences of 46 paddy soils were not dominated by betaproteobacterial clade II nosZ sequences, although they were ubiquitous. The same applied to the 16S rRNA sequences of Rhodocyclales or Nitrosomonadales.

Conclusions: The results indicated that betaproteobacterial N2O reducers potentially serve as powerful N2O sinks. Betaproteobacteria holding clade II nosZ can be targets of biostimulation, although further studies are required to understand their ecophysiology.

Aims: L-theanine, a non-protein amino acid derived from green tea, was synthesized by a relatively substantial amount of γ-glutamylmethylamide synthetase (GMAS) and polyphosphate kinase (PPK) without efficient recycling. This study establishes a cost-efficient, industrially scalable, and continuous biocatalytic platform for sustainable L-theanine production.

Methods and results: A functional catalyst system was engineered by fusing GMAS and PPK with the cell wall-binding domain derived from Listeria monocytogenes p60 protein (Lm-p60). The enzyme complex was immobilized onto Gram-positive Enhancer Matrix (GEM) particles, enabling facile separation and reuse over catalytic cycles. The enzymes were reusable and could be applied for 6 cycles with L-theanine yield achieving 86%-93%.

Conclusions: The reusable catalyst demonstrates operational sustainability over multiple cycles, offering cost savings and continuous utility.

Aim: We investigated the effects of plant growth-promoting bacteria (PGPB) on the growth and nutrition of coffee seedlings and the biological control of coffee leaf rust (Hemileia vastatrix), brown eye spot (Cercospora coffeicola), and leaf blight (Boeremia coffeae).

Methods and results: In the first part of the study, nineteen PGPB strains obtained in the phyllosphere, endosphere and rhizosphere of coffee and other hosts, produced varied metabolites related to plant growth and biological control. Two coffee cultivars were treated with the bacterial strains, but cultivar Catuaí Amarelo IAC 62 was less responsive to the treatments. Five rhizospheric strains, from different genera, Bacillus cereus (Rb1), Pseudomonas koreensis (Rb2b), Enterobacter mori (Mn2), B. safensis (Ob3a), Enterobacter cloacae (RBca5) and two endophytic strains, Enterobacter hormaechei (EOb1) and Paraburkholderia caribensis (Beca88) enhanced seed germination, plant biomass, and nutrient accumulation in cultivar 'Catuaí Vermelho' IAC144 seedlings. In the second part of the study, three strains, the phyllospheric Pseudomonas gozinkensis (Mn1F), the endophytic Paraburkholderia caribensis (BEca88) and the rhizospheric Enterobacter cloacae (RBca5) reduced the severity of coffee leaf rust, brown eye spot and leaf blight.

Conclusions: PGPB from different genera, obtained in varied hosts and habitats showed positive effect, improving plant fitness and controlling important coffee diseases, standing out the strains Pseudomonas gozinkensis (Mn1F), Paraburkholderia caribensis (IAC-BEca-088) and Enterobacter cloacae (IAC-RBca5).

Aim: The present work investigated the efficacy of native biocontrol candidates (antagonists) against aflatoxins, ochratoxin A, and fumonisins produced by native mycotoxigenic fungi isolated from Malaysia at different pathogen: antagonist inoculum ratios on grain corn agar and grain corn kernels.

Methods and results: Five pathogen: antagonist inoculum ratios (100:0, 75:25, 50:50, 25:75, 0:100) were employed. Non-aflatoxigenic Aspergillus flavus Af1KD and Af5TD, and Penicillium janthinellum were used against aflatoxin B1 (AFB1) and aflatoxin B2 (AFB2) by A. flavus. Against ochratoxin A (OTA) by A. niger, and fumonisin B1 (FB1) and fumonisin B2 (FB2) by Fusarium verticillioides and F. proliferatum, respectively, the antagonists Trichoderma asperelloides, T. asperellum, and T. harzianum were used. Non-aflatoxigenic A. flavus Af1KD was the most effective against AFB1 and AFB2 at all tested ratios and substrates. All Trichoderma spp. were effective against OTA by A. niger on grain corn agar at all tested ratios. T. asperelloides and T. asperellum were effective against FB1 and FB2 produced by F. verticillioides at all tested ratios and substrates. T. asperelloides was effective against FB1 and FB2 by F. proliferatum at all tested ratios and substrates.

Conclusion: The native biocontrol candidates were effective against mycotoxigenic fungi and mycotoxin production on grain corn agar and grain corn kernels, and could be developed into biocontrol agents.

Aims: This study evaluates the effectiveness of two standard sterilization methods on microorganisms in bentonite, which is proposed as a buffer around metal canisters containing long-lived radioactive waste. Bentonite, as a natural clay, contains microorganisms with enhanced resistance to harsh conditions and the ability to reactivate upon decompaction. Sterile controls are crucial in experiments estimating the impact of microorganisms on nuclear waste repositories. Yet, the effectiveness of common sterilization methods on bentonite microorganisms has not been fully evaluated.

Methods and results: two methods were compared: dry heat (nine cycles at 121°C for 4 hours) and gamma irradiation (10 to 140 kGy at 147 Gy·min-1). Molecular-genetic, microscopic, and cultivation techniques were used to assess sterilization. Heat sterilization did not eliminate heat-resistant microorganisms, such as Bacillus, Paenibacillus, and Terribacillus, from bentonite powder even after nine heat cycles. However, bentonite suspended in deionized water was sterile after four heat cycles. In contrast, gamma irradiation effectively reduced microbial survivability above a dose of 10 kGy, with the highest doses (100-140 kGy) potentially degrading DNA.

Conclusions: Gamma irradiation at 30 kGy effectively sterilized bentonite powder. The findings of our experiments emphasize the importance of using appropriate sterilization methods to maintain sterile controls in experiments that evaluate the microbial impacts in nuclear waste repositories. However, further assessment is needed to determine the effects of potential alterations induced by gamma radiation on bentonite properties.

Aims: Plant Growth Promoting Rhizobacteria (PGPR) are ubiquitous among soil bacteria and aid in many growth-related functions for plants. Recent biotechnological advancements involving PGPRs have led to a growing desire to explore and uncover combinatorial or dual use PGPRs. Our study aimed to discover novel insecticidal phenotypes amongst PGPR libraries.

Methods and results: We screened, through survivorship bioassays, 502 endophytic PGPRs for insecticidal activity against Drosophila melanogaster (fruit flies). Initial bioassay screens were followed by higher (n) testing and subsequent insecticidal assays against 4 key pest species including Drosophila suzukii, Spodoptera frugiperda, Aphis gossypii, and Lygus lineolaris. Of the 502 endophytic PGPRs screened, 39 strains showed statistically significant mortality against insects with three strains killing four pest species and seven killing three pest species. The key insecticidal strains primarily consisted of Serratia marcescens and Bacillus velezensis.

Conclusions: In total, ∼8% of strains tested showed insecticidal phenotypes. The fast screening methodology was successful in uncovering dual use PGPRs. Some bacteria were broad spectrum insect killers and others were more specific to a particular pest.

Aim: Combatting Pseudomonas aeruginosa, known for its robust biofilm formation, presents significant challenges in healthcare, food, and industry. Phages offer promising alternatives against this resilient pathogen. We aim to demonstrate their viability as alternative therapeutic and decontamination options.

Methods and results: We introduce the lytic activity and decontamination efficacy of Pseudomonas phage MME, isolated from sewage, on solid surfaces, as well as on its biological and genomic characterization. The phage showed lytic activity against both antibiotic-resistant clinical strains and reference strains. About 90% of the phage adsorbed to its host within 20 minutes, with an average burst size of ∼53 PFU per infected cell. The bactericidal effect on host at the 8th hour showed a 95% killing efficiency. Additionally, phage MME effectively reduced bacterial loads on glass, plastic, and metal surfaces, simulating hospital environments. Confocal laser scanning microscopy demonstrated the phage's bactericidal activity on glass surfaces at the 8th and 12th hours, preventing biofilm formation. Bioinformatic analysis confirmed that phage MME represents a new species within the Bruynoghevirus genus. Comparative genomic analysis revealed no virulence factors within the phage MME genome.

Conclusions: These findings highlight the potent lytic activity of phage MME against P. aeruginosa, underscoring its potential as a valuable tool in combatting this pathogen and its suitability for diverse applications, including as a decontaminating agent.

Aims: The World Health Organization has identified ESKAPE bacteria and Candida auris as priority pathogens, emphasizing an urgent need for novel antimicrobials to combat them. This study aimed to explore the therapeutic potential of antimicrobial peptidomimetics, specifically peptoids with sequence-specific N-substituted glycines, against ESKAPEE pathogens, including metallo-β-lactamase (MBL) producers, as well as C. auris strains.

Methods and results: This study evaluated activity of the peptoids against the multidrug-resistant priority pathogens. The peptoid TM8 (with an N-decyl alkyl chain) demonstrated a geometric mean minimum inhibitory concentration (MIC) of 7.8 μg ml-1 against MBL-producing bacteria, and 5.5 μg ml-1 against C. auris. TM8 showed synergy with ciprofloxacin, enhancing its effectiveness 4-fold against NDM-1-producing Klebsiella pneumoniae. No antagonism was seen when TM8 was used with either conventional antibiotics or antifungals. Peptoids that had therapeutic indices below 3 were generally more hydrophobic, due to either alkyl chains or bromine. Scanning electron microscopy and live-dead staining assay on peptoid-treated C. auris confirmed morphological changes and killing activity, respectively. Furthermore, the peptoid could effectively inhibit biofilm formation by C. auris.

Conclusion: Peptoids demonstrated antibacterial activity against ESKAPEE, particularly against MBL-producing Gram-negative bacteria. Additionally, they exhibited antifungal and anti-biofilm activities against C. auris strains.

Aims: Coral bleaching occurs when coral colonies lose their Symbiodiniaceae partner and turn pale or white. Although this event is generally temperature-induced, there is also the possibility of holobiont microbial infection and dysbiosis. To address this issue, this study was conducted to investigate the diversity and composition of Symbiodiniaceae and bacteria in healthy and bleached colonies of Porites lutea collected from eastern Shenzhen.

Methods and results: Internal transcribed spacer 2 and 16S amplicon sequencing analysis were used to explore the diversity and composition of Symbiodiniaceae and bacteria in healthy and bleached colonies of P. lutea. Bacterial diversity and richness were significantly higher in bleached colonies than in healthy colonies (P < 0.05), whereas the diversity and richness of Symbiodiniaceae showed no significant changes. The bleaching event exerted a more significant impact on Symbiodiniaceae composition, which differed between healthy and bleached colonies (PERMANOVA, F = 8.246, P < 0.05). In terms of composition, Clade C (Cladocopium) was the predominant Symbiodiniaceae, whereas subclade C116 and C2r were significantly less abundant in bleached colonies than in healthy colonies (P < 0.05). The phyla Bacteroidetes, Acidobacteria, and Actinobacteria were significantly more abundant in bleached colonies than in healthy colonies (P < 0.05). The sulfate-reducing bacteria (SRB) Desulfobulbus and Desulfobacter at the genus level and Desulfobacterales and Desulfuromonadales at the order level were significantly more abundant in bleached colonies than in healthy colonies (P < 0.05). The co-occurrence patterns of Symbiodiniaceae and bacteria revealed a negative correlation of Desulfofaba, Desulfovibrio, Desulfarculus, and Desulfobulbus with Endozoicomonas, a very common symbiotic bacterial genus found in corals.

Conclusion: Coral bleaching may be associated with significant shifts in microbial communities, including increased SRB abundance, which may disrupt microbial balance and contribute to bleaching.

Aim: This study aimed to investigate the bacteriology of cold smoked salmon (CSS), specifically changes in the bacterial quality (total viable count and total Enterobacteriaceae count), the concentration of spoilage bacteria (lactic acid bacteria, hydrogen sulphide producing bacteria and Pseudomonas spp.) and Listeria monocytogenes during salting, washing, smoking, maturation, packaging and chilled storage.

Methods and results: In-plant and laboratory based studies were undertaken. The salt concentration, pH and aw of the commercial product were 3.8% (w/w), 5.9% and 0.95%, respectively while those of the laboratory prepared CSS were 1.1%, 6.2%, and 0.94%. Although the CSS preparation process enhanced microbial quality, as determined by significant (P < 0.05) reductions in indicator and spoilage bacterial counts, L. monocytogenes was unaffected and all bacteria showed significant (P < 0.05) growth during chilled storage of the final product.

Conclusions: The microbial quality and safety of CSS is reliant on using uncontaminated fillets, good hygiene practices and ensuring that the shelf life does not afford L. monocytogenes sufficient time to exceed the 100 cfu g-1 maximum allowed in current EU legislation (EC 2073/2005).