Journal of Applied Microbiology最新文献

Aims: Myrtle rust, caused by the obligate pathogen Austropuccinia psidii, is a significant disease of myrtaceous plants. Species in Australia, such as Rhodamnia rubescens, are now critically endangered as a result of this disease. This research aimed to evaluate the culturable fungal communities present on, and within, leaves of symptomatic and asymptomatic R. rubescens plants as inhibitors of myrtle rust disease. We hypothesized that microbes present in asymptomatic leaves may possess biocontrol activity, thereby providing a mechanism of resistance observed in the field.

Methods and results: Fungal communities were isolated on three types of media and were identified using ITS sequencing. Of the 143 isolates obtained from both leaf types, germinating spores from nine isolates from the genera Nemania, Corynespora, Cladosporium, Pestalotiopsis, Quambalaria, Kalmanozyma, and Coniothyrium were found to inhibit the germination of A. psidii spores in vitro. However, no link was found between biocontrol activity of the isolates recovered and the degree of disease found on R. rubescens leaves. Isolates were also screened for antifungal activity during active hyphal growth using an unrelated pathogenic fungus Stagonosporopsis cucurbitacearum to test for broader bioprotective activity.

Conclusions: Isolates with antagonistic activities could be further explored in conservation efforts to protect plants against A. psidii symptoms, either in isolation, as part of a synthetic microbial community, or in more agricultural contexts to improve food security.

Aims: Arcobacter butzleri, a widespread bacterium linked to gastrointestinal disease, can bypass host colonization resistance mechanisms; however, its response to short-chain fatty acids (SCFAs) remains poorly understood. This study investigated the impact of SCFAs on A. butzleri's survival and virulence.

Methods and results: Eight A. butzleri isolates were assessed under varying concentrations of individual SCFAs and mixtures (m-SCFAs). Higher SCFAs concentrations inhibited bacterial growth in a strain-dependent manner. Transcript analysis of putative virulence genes revealed upregulation of ciaB and flaA across most m-SCFAs concentrations, while luxS expression increased at 90 mM. SCFAs generally reduced bacterial motility, with sodium propionate reducing motility but enhancing biofilm-forming ability in the model strain. Additionally, SCFAs exposure decreased the ability of A. butzleri to adhere to and invade the Caco-2 intestinal epithelial cell line. Whole-genome sequencing of the eight A. butzleri isolates revealed extensive genetic diversity, particularly in virulence- and stress-associated genes, although consistent genotype/phenotype correlations were not observed.

Conclusions: Altogether, these findings demonstrate that SCFAs modulate A. butzleri survival and virulence, providing novel insights into their significance in shaping pathogen behaviour and host-pathogen interactions.

Glycyrrhiza glabra is a medicinal legume species that is adapted to arid and saline environments, as well as climate stressors such as drought, salinity, and extreme heat. This review highlights the latest developments in understanding the microbial communities associated with G. glabra, which enhance stress tolerance through nutrient acquisition, phytohormone modification, the production of antioxidants, and osmotic regulation. This review synthesizes research on the distribution, diversity, and functionality of these microbial communities, including endophytes, rhizobacteria, and arbuscular mycorrhizal fungi within the ecological context of degraded and marginal soils, which functionally enhances G. glabra as a model plant for studying plant-microbial interactions in extreme environments. We specifically highlight the microbial regulation of glycyrrhizin biosynthesis, a critical defense-related secondary metabolite with known therapeutic applications. Finally, we present an overview of new and emerging multi-omics tools that elucidate the molecular mechanisms underpinning these beneficial microbial interactions, and their potential in developing bio-inoculants for climate-resilient agriculture and providing a blueprint for harnessing native microbial partnerships to enhance plant survival, productivity, and soil restoration under climate uncertainty.

Aim: To isolate bacteria from grapevine leaves and vineyard soil and evaluate their putative modes of action against the fungus Botrytis cinerea, which causes grape bunch rot.

Methods and results: In this study, we isolated 188 bacteria from soil and leaves, collected from two vineyards in Stellenbosch. Dual culture assays were used to screen the isolates against three Botrytis cinerea strains. Nine isolates (8 Bacillus species and 1 Pantoea agglomerans) with ≥60% antifungal activity against the three B. cinerea strains were identified and further characterized. The antifungal activity declined at low pH with only 6 of the isolates displaying antifungal activity at pH 5. All strains produced chitinase, while only five produced glucanase as part of their antifungal activity. The cell-free supernatants of B. nakamurai B4001 and B4022 strongly inhibited spore germination and mycelial growth of B. cinerea strains. The strong antifungal activity was linked to the lipopeptide families of iturins, surfactins, and fengycins.

Conclusions: This study shows that inter- and intraspecific variability in Bacillus spp. antifungal activity against B. cinerea is largely attributed to divergence in lipopeptide composition profiles. Most importantly, among the iturin families, a higher potency in bacillomycin D-producing strains compared to iturin A producers was evident.

Aims: Brewing yeast strain selection and management are critical in beer production, influencing flavor profiles and overall quality. This study investigates the potential of MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) for characterizing and differentiating brewing yeast strains associated with various beer styles.

Methods and results: We analyzed 77 commercial yeast strains used to produce ale, lager, cider, mead, and low-alcohol beer, using MALDI-TOF MS in both high (m/z 2000-20 000) and low (m/z 500-4000) mass ranges. Spectra were analyzed using informatics-assisted hierarchical cluster analysis, multidimensional scaling (MDS), and linear discriminant analysis (LDA) to evaluate strain relationships and beer style associations. Results demonstrated that high mass range data formed an excellent basis for species-level identification, while low mass range data was more diverse and represented information that was more strain-specific.

Conclusions: Both MDS and hierarchical clustering of combined low- and high-range MALDI-TOF spectra identified relationships between certain strains that correlated with their brewing recommendations. However, the use of LDA presented the clearest correlation of strain relationships with beer styles recommended by the commercial yeast producer.

Aims: We aim to evaluate the productivity of shiitake strains under warm cultivation temperatures using alternative substrates from neotropical tree species, addressing the challenges of global warming and substrate availability.

Methods and results: Four strains (one control and three warm-tolerant candidates) were cultivated on sawdust from Quercus, Carpinus, and Bursera at 18°C and 25°C. Strain identity was confirmed via phylogeny. Biological efficiency (BE), yield, production rate, and lignocellulose degradation were measured. All strains were taxonomically confirmed as Lentinula edodes. The highest BE was 107%, recorded in Quercus at 18°C, although it was highly variabile (30%). Warm-tolerant strains IE-3012, IE-3013, and IE-3014 consistently outperformed the control at 25°C, particularly on Quercus. There was mushroom production in Bursera, although it was lower. Lignin was the most consumed lignocellulosic fraction across all conditions.

Conclusions: This study confirms that the suspected heat-tolerant L. edodes strains can be cultivated at 25°C, using alternative substrates such as Bursera, though substrate choice significantly affects productivity. Strain IE-3013 performed best, positioning it as a promising candidate for warm-climate cultivation. Cold-water immersion successfully induced the development of fruiting bodies across studied conditions, supporting its use in the shiitake cultivation process.

Aim: The halotolerant endophytic bacterial Pseudomonas strain EB3 isolated from the roots of the mangrove plant species Avicennia alba, has been reported to promote plant growth and mitigate the adverse effects of salt stress. However, the genetic mechanisms of the strain that may explain these processes are unknown. This study aimed to determine the whole genome sequence of EB3 and conduct expression analysis of EB3 genes putatively involved in salt tolerance and plant growth promotion.

Methods and results: EB3-inoculated banana (Musa acuminata cv. Berangan) plantlets were subjected to 100 mM sea salt. These inoculated plants exhibited significantly improved growth compared to non-inoculated controls under the same salinity stress. Whole-genome sequencing of EB3 revealed a genome size of 6 006 826 bp. Phylogenetic analysis based on whole-genome comparison indicated that EB3 is closely related to Pseudomonas juntendi. Functional annotation of the genome identified a large number of genes associated with key biological processes, including stress resistance, iron uptake system, plant root colonization, and plant growth promotion. The increased expression of succinate-semialdehyde dehydrogenase (gabD), pyrroloquinoline quinone biosynthesis proteins (pqqBDEF), acetylglutamate kinase (argB), NADP-specific glutamate dehydrogenase (gdhA), N-acetylglutaminylglutamine synthetase (ngg), and superoxide dismutase family protein (sodC) genes in EB3, when EB3-inoculated plants were placed under salt stress, further supported their potential involvement in salt tolerance and growth-promoting activities.

Conclusion: Together, the genomic insights and gene expression data confirm the functional potential of the EB3 strain as a plant growth-promoting bacterium (PGPB) even under saline conditions.

Aims: Metal resistance genes (MRGs) and virulence factor genes (VFGs) are driven by environmental factors and host immunity, respectively, and they are traditionally considered to evolve independently. However, their co-selection dynamics in landfill leachates remain poorly characterized. In this study, a multi-regional metagenomic assessment integrating environmental gradients was first presented to reveal how heavy metals shape MRG-VFG interactions and associated ecological risks in landfill leachates.

Methods and results: Landfill leachates were collected from 13 landfills spanning six regions in China. Multi-regional metagenomic sequencing combined with co-occurrence network analysis was applied to examine pathogen-gene relationships. The results revealed pronounced regional disparities in pathogen, MRG, and VFG distribution, alongside shared features. Staphylococcus aureus and Pseudomonas aeruginosa were identified as dominant pathogens. tufA and gyrA emerged as conserved VFGs, whereas arsB and copA represented dominant MRGs. Network analysis revealed Escherichia coli, Salmonella enterica, and Acinetobacter baumannii as central nodes carrying overlapping functional genes, forming a "metal resistance-virulence" synergy module. Redundancy analysis revealed that specific heavy metals (Cu, Zn, Cr, and As) were crucial for the formation and stability of "pathogen-MRG-VFG" functional assemblies.

Conclusions: This study addresses a critical knowledge gap by integrating multi-regional metagenomic evidence with environmental selection pressures. MRGs conferred survival advantages and synergized with VFGs to enhance pathogen infectivity. These findings provide insight into MRG-VFG co-selection mechanisms in landfill leachates and guide targeted monitoring to mitigate environmental and health risks.

Introduction: In order to understand the emergence, persistence, and transmission of Campylobacter jejuni in livestock, this longitudinal study characterized the C. jejuni population in young calves and assessed the impact of exposure to wild birds during the pre-weaning period.

Methods and results: Faecal samples were collected on eight occasions from 48 calves housed in three pens between birth and 10 weeks of age, two of the pens being covered with orchard netting. From the 250 C. jejuni isolates obtained from the positive faeces, seven distinct sequence types (7-gene legacy MLST) were identified, with high genetic similarity of circulating strains. On each pen, sequential dominance of ST was observed, with ST-508 and ST-50 prevalent in calves under 4 weeks old, and ST-520 or ST-422 prevalent in the 8- to 10-week-old calves. Exposure of calves to wild birds did not influence genotypes distribution, α-diversity, and community dissimilarity. However, a difference in C. jejuni populations between the two groups of calves that were not exposed to birds suggests that calving rank may shape the type and succession of ST detected over time.

Conclusion: This study provided no evidence for exposure to wild birds being a driver for C. jejuni population changes in healthy pre-weaned calves.

Aims: The study aimed to investigate the anti-methicillin-resistant Staphylococcus aureus (MRSA) and anti-biofilm activity of 3-methoxy-5-hydroxy-2-(3-methyl-2-butenyl) bibenzyl (DELC) isolated from Cajanus cajan (L.) Millsp (pigeon pea) leaves, while evaluating its biocompatibility and exploring its potential as an antibiotic alternative.

Methods and results: DELC exhibited potent anti-MRSA activity, with a minimum inhibitory concentration (MIC) of 3.12 μg/mL and MBC of 6.25 μg/mL. At 2 × MIC, it achieved complete eradication of 106 CFU/mL MRSA within 120 min, demonstrating faster bactericidal action than vancomycin.

Antibiofilm studies: 2 × MIC DELC inhibited biofilm formation as effectively as 4 × MIC vancomycin. In mature biofilms, merely 1/2 × MIC DELC penetrated and eliminated a portion of embedded viable bacteria-a feat unattainable even with 8 × MIC vancomycin.

Mechanistic studies: DELC induced oxidative stress, generating ROS that damaged the bacterial membrane, causing nucleic acid leakage. It also suppressed α-hemolysin secretion.

Rna-seq analysis revealed: At 1 × MIC, DELC blocked ATP synthesis and repair systems, leading to metabolic inhibition and virulence attenuation. At ≥2 × MIC, it directly lysed bacterial cells.

Biocompatibility: DELC showed no hemolysis or cytotoxicity, indicating excellent safety.

Conclusions: DELC demonstrates potent anti-MRSA activity characterized by rapid bactericidal effects, a concentration-dependent dual mechanism-metabolic inhibition at low concentrations progressing to direct cellular lysis at higher concentrations, and superior antibiofilm capacity. Its outstanding biocompatibility strongly supports its clinical translation potential.