Identification of the Biosynthetic Pathway of Glycine Betaine That Is Responsible for Salinity Tolerance in Halophilic Thioalkalivibrio versutus D301

Unveiling Salmonella Derby Survival: Stress Responses to Prolonged Hyperosmotic Stress

The traditional marination process enhances food flavor and inhibits microbial growth. However, in hyperosmotic environments, microorganisms can activate stress responses to ensure survival, potentially compromising food safety. This study investigated the osmotolerance mechanisms of Salmonella Derby (S. Derby) by comparing a wild-type strain (S. D-WT) and an osmotolerant strain (S. D-OT) under NaCl-induced hyperosmotic stress. Both strains were subjected to 0.85%, 4%, and 16% NaCl for 0, 8, and 16 days, and their growth behavior, membrane integrity, intracellular osmoprotectant content, and transcription of related genes were evaluated. By day 16, both strains showed a growth delay of approximately 3 h. S. D-OT maintained better membrane integrity and exhibited higher intracellular levels of osmoprotectants (K⁺, trehalose, and proline), which aligned with the upregulation of the transcriptional levels of kdpC, kuP, rpoS, and proU. These findings indicated that S. D-OT achieved improved osmotic stress tolerance by regulating osmoprotectant synthesis and maintaining intracellular homeostasis. In contrast, S. D-WT displayed greater resistance to multiple antibiotics (gentamicin, ciprofloxacin, trimethoprim-sulfamethoxazole, and chloramphenicol) under 4% and 16% NaCl conditions, which may pose a higher food safety risk. Overall, this study provides insights for improving microbial control strategies in preserved foods and mitigating foodborne disease risks.

Metabolomics of Benzene Exposure and Development of Biomarkers for Exposure Hazard Assessment

Benzene, a common industrial solvent, poses significant health risks including poisoning and hematopoietic diseases. However, its precise toxicity mechanisms remain unclear. To assess the health impact of prolonged benzene exposure through metabolomic analyses of exposed workers and benzene-poisoned mice, aiming to identify biomarkers and minimize occupational hazards. This study compared 18 benzene-exposed workers with 18 non-exposed workers, matching for age, lifestyle, and BMI. The metabolites in the workers' samples were analyzed using ultra-high-performance liquid chromatography and mass spectrometry. A larger study included 118 exposed and 158 non-exposed workers, incorporating surveys and routine blood and urine tests with differential metabolites targeted via an enzyme-linked immunosorbent assay. The animal studies consisted of two 15- and 60-day benzene staining and control experiments on 28 C57BL/6J mice, followed by sample collection and organ analysis. The data analysis employed eXtensible Computational Mass Spectrometry (XCMS), Python, MetaboAnalyst 6.0, and SPSS24.0. The exposed workers exhibited altered metabolites indicating external benzene exposure, lower glucose levels, and changes in white blood cell counts and urinary ketone bodies. The plasma metabolomics revealed disturbances in energy and lipid metabolism. The benzene-exposed mice displayed reduced weight gain, behavioral changes, and organ damage. Oxidative stress and abnormal purine and lipid metabolism were observed in both the long-term benzene-exposed workers and benzene-exposed mice. Metabolic markers for the early detection of benzene exposure hazards were identified, underscoring the need to mitigate occupational risks.

The polyextremophile Natranaerobius thermophilus adopts a dual adaptive strategy to long-term salinity stress, simultaneously accumulating compatible solutes and K. Appl Environ Microbiol 2024;90:e0014524. [PMID: 38578096 PMCID: PMC11107154 DOI: 10.1128/aem.00145-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The bacterium Natranaerobius thermophilus is an extremely halophilic alkalithermophile that can thrive under conditions of high salinity (3.3-3.9 M Na+), alkaline pH (9.5), and elevated temperature (53°C). To understand the molecular mechanisms of salt adaptation in N. thermophilus, it is essential to investigate the protein, mRNA, and key metabolite levels on a molecular basis. Based on proteome profiling of N. thermophilus under 3.1, 3.7, and 4.3 M Na+ conditions compared to 2.5 M Na+ condition, we discovered that a hybrid strategy, combining the "compatible solute" and "salt-in" mechanisms, was utilized for osmotic adjustment dur ing the long-term salinity adaptation of N. thermophilus. The mRNA level of key proteins and the intracellular content of compatible solutes and K+ support this conclusion. Specifically, N. thermophilus employs the glycine betaine ABC transporters (Opu and ProU families), Na+/solute symporters (SSS family), and glutamate and proline synthesis pathways to adapt to high salinity. The intracellular content of compatible solutes, including glycine betaine, glutamate, and proline, increases with rising salinity levels in N. thermophilus. Additionally, the upregulation of Na+/ K+/ H+ transporters facilitates the maintenance of intracellular K+ concentration, ensuring cellular ion homeostasis under varying salinities. Furthermore, N. thermophilus exhibits cytoplasmic acidification in response to high Na+ concentrations. The median isoelectric points of the upregulated proteins decrease with increasing salinity. Amino acid metabolism, carbohydrate and energy metabolism, membrane transport, and bacterial chemotaxis activities contribute to the adaptability of N. thermophilus under high salt stress. This study provides new data that support further elucidating the complex adaptation mechanisms of N. thermophilus under multiple extremes.IMPORTANCEThis study represents the first report of simultaneous utilization of two salt adaptation mechanisms within the Clostridia class in response to long-term salinity stress.

Improving Microbial Cell Factory Performance by Engineering SAM Availability

Methylated natural products are widely spread in nature. S-Adenosyl-l-methionine (SAM) is the secondary abundant cofactor and the primary methyl donor, which confer natural products with structural and functional diversification. The increasing demand for SAM-dependent natural products (SdNPs) has motivated the development of microbial cell factories (MCFs) for sustainable and efficient SdNP production. Insufficient and unsustainable SAM availability hinders the improvement of SdNP MCF performance. From the perspective of developing MCF, this review summarized recent understanding of de novo SAM biosynthesis and its regulatory mechanism. SAM is just the methyl mediator but not the original methyl source. Effective and sustainable methyl source supply is critical for efficient SdNP production. We compared and discussed the innate and relatively less explored alternative methyl sources and identified the one involving cheap one-carbon compound as more promising. The SAM biosynthesis is synergistically regulated on multilevels and is tightly connected with ATP and NAD(P)H pools. We also covered the recent advancement of metabolic engineering in improving intracellular SAM availability and SdNP production. Dynamic regulation is a promising strategy to achieve accurate and dynamic fine-tuning of intracellular SAM pool size. Finally, we discussed the design and engineering constraints underlying construction of SAM-responsive genetic circuits and envisioned their future applications in developing SdNP MCFs.