Letters in Applied Microbiology最新文献

Halorubrum salinarum RHB-CT, an archaeon known for its extreme halophilic, neutrophilic, and mesophilic characteristics, was studied for its carotenoids' potential as singlet oxygen antioxidants. This resilient organism thrives optimally at pH 7, 45°C temperature, and 25%-30% salinity. Optimization revealed that pH 7, 30°C temperature, and 25% salinity enhanced carotenoid production, likely due to oxidative stress and slower growth at lower temperatures, which in turn stimulate secondary metabolism. Carotenoids identified were haloxanthin (38%), bacterioruberin (BRB) (20%), monoanhydro-bacterioruberin (MABR) (20%), and one unidentified compound (23%). A 40 µM crude extract showed the highest singlet oxygen antioxidant activity at 19.68%, comparable to butylated hydroxyanisole and butylated hydroxytoluene.

Rice leaves harbor a diverse agriculturally important bacteriome. Using different dilutions and media, 20 bacterial isolates were obtained from the diseased and healthy leaves of two rice cultivars (cv. BPT-5204 and cv. Tetep). Later, the taxonomy was deduced based on the 16S rDNA sequences, which revealed 17 bacterial species belonging to 13 genera. The antifungal activity of 17 bacteria was tested against Rhizoctonia solani, which showed that Bacillus cereus, Stenotrophomonas maltophilia, and Acinetobacter lwoffii exhibited the mycelial inhibition of 65.18%, 61.85%, and 61.85%, respectively. Further, six selected bacteria (treatments: T1-T6) in three different methods of inoculation (methods: M1-M3) were tested on-field against sheath blight (ShB) for two consecutive Kharif seasons (2022 and 2023). The two-season data indicated a statistically insignificant effect of methods on the % disease index (PDI) (40.51-42.47), whereas different bacteria treatments (T1-T6) showed a significant impact on PDI (29.15-52.08). S. maltophilia isolated from the diseased BPT-5204 was superior to all other strains in reducing the PDI (29.15). We successfully isolated and functionally characterized 17 bacteria from the artificially diseased contrasting genotypes. This study demonstrated that rice lesions naturally harbor a diverse bacterium with antifungal effects that can be used to develop non-chemical-based disease management strategies.

Mycoplasma amphoriforme is an emerging respiratory pathogen for which little is known about the population structure or transmission dynamics. In this study, we developed the first multilocus sequence typing (MLST) scheme for M. amphoriforme and applied it to a previous genomic data set. The genomes of seven M. amphoriforme isolates from the UK and Denmark were sequenced and used to develop the MLST scheme based on loci used for previous Mycoplasma MLST schemes. The resulting MLST scheme consisted of four loci (gyrB, atpG, uvrA, and rpoB) and was applied to 20 previously sequenced genomes obtained from the UK and France/Tunisia. From the 27 sequences examined, 13 sequence types were identified. A phylogenetic tree of concatenated sequences showed a comparable topology to a previously described tree based on whole genome data. Additionally, the MLST scheme corroborated the previous suggestion of possible healthcare-associated transmission of M. amphoriforme between two separate patients. The MLST scheme gave a population structure analysis comparable to previous whole-genome-based analyses.

Human milk has a low microbial biomass with a microbiome dominated by typical skin and oral taxa, raising concerns about contamination during sample collection. However, to date, no study has directly compared samples collected with and without aseptic technique, leaving questions related to potential contamination within the field. To address this, we compared the microbiota of hand-expressed milk samples collected from 23 mothers before and after cleansing of the hands and breast. Metataxonomic analysis showed that taxonomic profiles were largely unaffected by cleansing, with only Rothia mucilaginosa significantly more abundant in non-aseptically collected samples (P = 0.007). Although aseptically and non-aseptically collected samples were taxonomically similar, there was a higher level of bacterial richness (P = 0.003) and evenness (Shannon diversity, P = 0.0002) in non-aseptically collected samples, suggesting that multiple low-abundance taxa are introduced via skin contamination. These findings support the use of aseptic collection methods to minimize external contamination and accurately assess milk microbial diversity. Importantly, they also suggest that common skin and oral taxa detected in human milk are likely true members of the mammary microbiome.

The regulatory mechanisms underlying ploidy dynamics in cyanobacteria under phosphorus (P) limitation remain poorly understood. In this study, we investigated the impact of phosphate deprivation on the polyploidy of Synechocystis sp. PCC 6803 through integrated approaches combining spectrofluorometry, flow cytometry, comparative transcriptomics, Pho regulon prediction, and enzymatic activity assays. Our results revealed a significant reduction in genomic DNA content (P < 0.01) during cultivation in phosphate-free BG11 medium, with average genome copy numbers decreasing from 24.34 ± 0.27 in standard BG11 to 6.18 ± 0.25 under P-depleted conditions (P < 0.01). Transcriptomic analysis demonstrated marked upregulation of genes associated with two-component signaling systems, ABC transporters, and nucleotide metabolism, while DNA replication, homologous recombination, and mismatch repair pathways were significantly downregulated (P < 0.05). Concurrently, alkaline phosphatase activity exhibited a substantial increase (P < 0.01), suggesting enhanced phosphate mobilization. These findings collectively indicated that genome copy number in Synechocystis sp. PCC 6803 was dynamically regulated through the coordinated interplay between DNA replication suppression and degradation activation in response to phosphorus availability. This work provides novel insights into the molecular basis of ploidy regulation in cyanobacteria and offers valuable implications for understanding analogous mechanisms in chloroplasts.

Maize, groundnut, and sorghum are important staple crops in several countries, but are prone to mycotoxin contamination. In the tropics and subtropics, Aspergillus flavus frequently contaminates those crops with aflatoxins and, sometimes, with cyclopiazonic acid (CPA). However, some genotypes cannot produce one or both toxins. In various countries, atoxigenic isolates of A. flavus are formulated into biocontrol products for field use to outcompete aflatoxin producers. The products effectively limit aflatoxin but their utility to reduce CPA remains unexplored. The abilities of four atoxigenic isolates (AF-) from Burkina Faso to control CPA by an isolate with high capacity to produce aflatoxins (AF+) and CPA was tested in co-inoculations at varying ratios (100+, 75+/25-, 50+/50-, 25+/75-, 100-), under simulated abiotic stress conditions. Experiments were conducted on 2% sorghum-based media at 0.95 and 0.90 water activity (aw), at 30°C and 37°C, for 12 days. CPA was quantified using liquid chromatography tandem mass spectroscopy. CPA concentrations gradually decreased as the proportion of atoxigenic isolates increased, with effectiveness varying depending on the environmental conditions.

Yersinia enterocolitica is one of the most important foodborne pathogens with significant impact on public health. It can be divided into six biotypes and approximately 60 O-serotypes, with O:3, O:9, O:8, and O:5,27 being predominantly associated with human yersiniosis. We present a two-group quadruplex real-time quantitative PCR (RT‒qPCR) for the patho-serotyping of Y. enterocolitica. The design of primers and probes within group 1 was based on sero-specific genes within the O antigen gene cluster, and those within group 2 were selected from the virulence markers and the restriction modification system to distinguish O:5,27 from O:5. The specificity was tested using reference strains, and was confirmed by a comparison with those obtained by a previous multiplex PCR. The limit of detection is 0.1 ng, or 104 copies μl-1 of genomic DNA, and the standard curves exhibited high linearity and correlation coefficients, demonstrating our assay's robustness. Among the 81 isolates used to evaluate the reproducibility, the results for 76 were consistent between the two approaches, indicating that the sensitivity of our RT‒qPCR is 100%, and the positive predictive value is 94%. Our assay can serve as a tool for identifying sources of Y. enterocolitica contamination and for epidemiological monitoring of this bacterium.

Maize (Zea mays L.) is the third most cultivated crop globally after wheat and rice. It is one of the important staple food crops in the tribal-inhabited forest areas in India, where reduced yield is observed due to lower soil nutrients. Biopriming with bacteria having plant growth promotion (PGP) effects could be an effective way to mitigate this problem. In this context, a potential Bacillus tequilensis LRB17 strain was bioprimed in maize cultivar for the first time for PGP. Treatment of maize with the bacterium could enhance seedling vigor by 19.56%. The root and shoot length and the root and shoot weights were enhanced by 120.21% and 121.41% and 43.03% and 40.07%, respectively. Average height of matured plants, average leaf area, and plant biomass could be enhanced by 19.30%, 30.47%, and 311.30%, respectively. Parenchyma cells in stems increased with well-developed bundle sheaths. The bacterium has been isolated from local millet crop landrace of "Koraput" area of the "Eastern Ghats" of India, which has been designated as "Globally Important Agricultural Heritage System (GIAHS)" by the United Nations. Hence, the native Bacillus tequilensis LRB17 posed as a potential bioagent for yield enhancement of maize for the benefit of tribal population.

The development of bioherbicides is often limited by low herbicidal activity. To address this challenge, we enhanced the virulence of Alternaria alternata DT-DYLC, a biocontrol strain against Chenopodium album L., through combined UV and nitrite mutagenesis. Mutant strain J exhibited 2.4-fold higher pathogenicity in detached-leaf assays and 7.19% greater efficacy in pot trials compared to the wild-type strain. Transcriptome analysis during infection revealed 3060 differentially expressed genes, with 257 linked to metabolic processes. Notably, 87 co-expressed up-regulated genes were enriched in cell wall degradation enzymes, fungal toxin synthesis, and toxic compound transport, suggesting enhanced virulence mechanisms in mutant J. This study demonstrates that classical mutagenesis effectively improves fungal pathogenicity, while transcriptomic insights into virulence-related pathways provide a foundation for optimizing bioherbicide strains and understanding A. alternata's pathogenic biology.

Recombinase polymerase amplification (RPA) is a powerful isothermal nucleic acid amplification technique, yet its efficiency is critically dependent on the catalytic efficiency of the recombinase UvsX, a key enzyme mediating homologous DNA pairing and strand exchange. To address this limitation, in this study, we developed a specific, sensitive, and robust RPA detection method by optimizing the UvsX enzyme through protein engineering and refining the RPA reaction system. By conducting comparative structural and functional analysis of UvsX orthologs from 13 Myoviridae phages, we identified critical determinants of recombinase activity within the Loop 2 domain of T4 UvsX. Furthermore, we systematically optimized the stoichiometric ratios of core enzymes and crowding agents to establish a robust RPA system. This system was subsequently integrated with lateral flow strips for point-of-need detection of highly lethal Vibrio parahaemolyticus in shrimp. Our results demonstrated that the engineered UvsXv1 variant exhibited significantly improved strand displacement activity, leading to enhanced RPA amplification efficiency and stability.