Letters in Applied Microbiology最新文献

Non-dairy probiotic formulations are gaining attention due to their health benefits, but it is essential to assess their ability to maintain probiotic viability while ensuring sensory acceptance, which may be achieved by the incorporation of fruit. This study evaluated the effect of pitaya pulp on probiotic viability, post-acidification, color, total phenolic compounds, and sensory characteristics of a cashew nut extract-based probiotic fermented beverage. Cashew nut extract was supplemented with 5% (B05) and 10% (B10) pitaya pulp and fermented by Streptococcus thermophilus and Lacticaseibacillus casei BGP93. The control (BC) contained no pulp. Pitaya pulp did not influence pH, titratable acidity, or probiotic counts, which ranged from 7.15 to 7.83 log CFU mL-1. However, it affected color parameters: treatments with pitaya pulp showed L values ∼12% and b* values 52%-73.7% lower than BC, while a* values were higher in B05 and B10, respectively, compared to BC. It also reduced phenolic compounds after 28 days (208.66, 124.70, and 134.50 µg EAG g-1 in BC, B05, and B10, respectively). Pitaya pulp enhanced appearance, flavor, overall acceptance, and purchase intention, with B05 achieving the highest scores. Its addition is a promising approach for developing probiotic plant-based fermented beverages.

In recent years, nucleic acid sequencing has been increasingly used in clinical pathogen detection. Typically, 20-100 million metagenomic reads are generated per sample, but 90%-99% originate from host nucleic acids, leaving only 1-2 million for microbial identification-potentially compromising detection sensitivity. Here, we present a novel duplex-specific nuclease (DSN)-based method to reduce host nucleic acid content in next-generation sequencing. Validated using mock communities and clinical samples, it yielded a 2- to 3-fold increase in pathogen RPM (reads per million) in metagenomic NGS (mNGS) and a more pronounced 3- to 10-fold improvement in probe-based targeted NGS (tNGS). Optimal performance was achieved with: 65°C annealing temperature; 2 μg Cot-1 DNA and 50 μmol rProbe as driver DNA; and 150 mmol·L-1 tetramethylammonium chloride (TMAC)-using 25 ng input nucleic acid for library preparation. The DSN workflow adds less than 30 min to library preparation and enables rapid, low-loss microbial enrichment, enhancing pathogen detection in clinical NGS. While effective, its host depletion efficiency could be further improved by expanding driver DNA coverage to additional abundant human genomic regions, such as LINE and LTR repeats.

The halotolerant methanotroph Methylotuvimicrobium alcaliphilum 20Z represents a promising platform for simultaneous methane mitigation and production of value-added metabolites, such as the single-cell protein. This study aimed to determine the optimal CH4/O₂ ratio and concentrations of key supplements [paraffin oil, folic acid (FA), and malic acid] in batch cultures to concurrently enhance biomass and protein yield. Under the optimized conditions (1:4 CH4:air, 2% (v/v) paraffin oil, 10 μg/L FA, and 1 mmol/L malic acid), maximum biomass and protein production reached 4.20 ± 0.19 g/L and 984.90 ± 45.34 mg/L, respectively. Intracellular glycogen content varied substantially between 50 and 800 mg/L. A notable shift in intracellular composition was observed during batch cultivation: rising biomass was associated with declining protein content but increasing glycogen reserves. These findings establish a foundation for rational media formulation and scale-up of M. alcaliphilum 20Z cultivation for industrial protein production.

Bacillus spp. can colonize various plant tissues, promoting growth and providing biocontrol. Bacillus amyloliquefaciens GZY63 exhibits strong antagonistic activity against anthracnose pathogens in Camellia oleifera. However, its potential as a biocontrol agent in Ca. oleifera remains underexplored, mainly because knowledge regarding its colonization behavior in this host plant is limited. In this study, we used a chloramphenicol-resistant GFP-tagged GZY63 strain to assess the colonization patterns of the bacterium in Ca. oleifera through quantitative Polymerase Chain Reaction (qPCR). In particular, we investigated the bacterium's colonization dynamics across three Ca. oleifera varieties, with a focusing on differences between the root and foliar inoculation methods. The results revealed that root inoculation of B. amyloliquefaciens GZY63 resulted in significantly higher colonization efficiency and more rapid bacterial translocation to leaf tissues than its foliar inoculation. Moreover, the colonization efficiency varied among the three Ca. oleifera varieties, indicating that host genotype influences the bacterium's endophytic compatibility. Although the underlying biochemical factors and regulatory mechanisms remain unclear, our results provide valuable insights into host-microbe interactions in Ca. oleifera. These findings provide a theoretical basis for optimizing the application of B. amyloliquefaciens GZY63 as biocontrol agent in Ca. oleifera and underscore the importance of selecting compatible host genotypes for effective microbial inoculation.

Group B Streptococcus (GBS) is a major cause of maternal and neonatal infections, complicated by increasing antimicrobial resistance and high virulence. In this study, from 235 vaginal swabs, 45 GBS isolates were identified and screened; 12 representative isolates (strong biofilm producers with the complete virulence gene profile) were selected for downstream analyses. Molecular analysis showed high prevalence of virulence genes (fbsA 95.5%, lmb 91.1%, pavA 88.8%, fbsB 86.6%) and biofilm-related genes (pil-1 88.8%, pil-2a 91.1%, pil-2b 84.4%). Subsequently, a Bifidobacterium bifidum (designated B. bifidum BB-6; GenBank accession number PX474696) isolated from human breast milk was used to prepare a cell-free supernatant (CFS). Gas chromatography-mass spectrometry analysis (GC-MC) of the CFS of B. bifidum identified several bioactive compounds, including acetic acid, propionic acid, and lactic acid. Checkerboard assays indicated synergism between CFS and penicillin/vancomycin, with a fractional inhibitory concentration index (FICI) of ≤ 0.5 in most cases. Sub-minimum inhibitory concentration (sub-MIC) of CFS significantly inhibited biofilm formation (P < 0.01), and quantitative real-time PCR (qRT-PCR) revealed downregulation of virulence (fbsB down -4.40-fold) and biofilm genes (pil-2b down -5.49-fold). These results highlight the therapeutic potential of B. bifidum CFS against GBS, warranting further studies to isolate active compounds and evaluate safety and efficacy in vivo.

Bacterial carotenoids are of significant industrial interest due to their bioactive properties. This study aimed to isolate carotenoid-producing bacteria from Egyptian agricultural land and screen key parameters to enhance their pigment yield. The most productive isolatesse were identified as Exiguobacterium acetylicum and Arthrobacter gandavensis. A one-variable-at-a-time approach revealed that maximum carotenoid production was highly strain-specific. Following cell disruption via mild acid hydrolysis, the optimal extraction solvents were pure acetone for A. gandavensis (4.74 mg L-1) and a 1:1 acetone:methanol mixture for E. acetylicum (5.87 mg L-1). While both strains achieved peak carotenoid production in nutrient broth at 48 hours and pH 6.0, their optimal growth temperatures diverged; A. gandavensis thrived at 35°C and E. acetylicum at 25°C. Liquid chromatography mass spectrometery analysis of A. gandavensis revealed a carotenoid profile containing zeaxanthin, decaprenoxanthin, bacterioruberin, and arthroxanthin. The extract exhibited mechanism-dependent antioxidant activity, most notably a robust peroxyl radical scavenging capacity (421.13 µM TE/mg in ORAC). These findings underscore the necessity of strain-specific screening to maximize the potential of bacterial sources for producing natural carotenoids with distinct antioxidant profiles.

Continuous cultivation can lead to soil nutrient imbalances and have adverse effects on soil rhizosphere microorganisms. This study investigated the impact of continuous cultivation of Salvia miltiorrhiza on rhizosphere soil microbial communities by comparing four planting durations: CK (no cultivation), D1 (annual planting), D2 (two consecutive years), and D3 (three consecutive years). High-throughput sequencing technology was used to analyze changes in rhizosphere soil microbial communities. The results revealed that the planted soil of Salvia miltiorrhiza exhibited lower abundances of beneficial bacteria such as Bacillus and Acidothermus compared to CK. The pathogenic fungus Fusarium was found to found to have the highest abundance in D2 soil. Linear discriminant analysis effect size analysis at the genus level identified several biomarkers, including g_Candidatus_Solibacter, g_Sphingomonas, g_RB41, and g_Chitinophaga as bacterial markers, while g_Talaromyces, g_Thermomyces, g_Trichothecium, g_Solicoccozyma, and g_Pseudopithomyces as fungal markers. Correlation analysis between these microbial markers and environmental factors showed that total nitrogen had a significant positive correlation with bacteria g_Candidatus_Solibacter and fungi g_Solicoccozyma, but a significant negative correlation with bacteria g_Sphingomonas and g_RB41. Soil organic matter showed a negative correlation with g_Sphingomonas; g_Candidatus Solibacter was negatively correlated with g_Sphingomonas.

Botryosphaeria dothidea is an important pathogenic fungus, which poses serious threats to crops and causes substantial economic losses. Plant essential oils (EOs) have strong antifungal activity and induce fruit resistance to microorganisms. The antifungal activity and mechanism of Mentha spicata EOs and major compounds against B. dothidea, and the extending shelf life of Actinidia chinensis fruit were investigated. The results showed that estragole was a most abundant in M. spicata EO compounds. Mentha spicata EOs, D-carvone, estragole, and fenchone exhibited strong inhibitory effects on B. dothidea. Mentha spicata EOs and fenchone had significantly increased the electrical conductivity of B. dothidea solution and caused a loss of nucleic acid and soluble protein. Mentha spicata EOs and estragole suppressed the cellulase and peroxidase of B. dothidea; however, fenchone promoted the xylanase activity. Botryosphaeria dothidea proliferation on A. chinensis fruit was inhibited by M. spicata EOs and major compounds during days 3 to 7 in situ. Mentha spicata EOs and fenchone promoted the A. chinensis fruit cellulase activity; however, the xylanase activity was significantly reduced. The peroxidase activity of A. chinensis fruit was increased by estragole. This study showed that M. spicata EOs has great potential as antifungal agent used for fruit postharvest.