Mass Spectrometry-Based Targeted Metabolomics Revealed the Regulatory Roles of Magnesium on Biofilm Formation in Escherichia coli by Targeting Functional Metabolites

2,5-Dihydroxyterephthalic Acid: A Matrix for Improved Detection and Imaging of Amino Acids

Amino acids (AAs), which are low-molecular-weight (low-MW) metabolites, serve as essential building blocks not only for protein synthesis but also for maintaining the nitrogen balance in living systems. In situ detection and imaging of AAs are crucial for understanding more complex biological processes. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a label-free mass spectrometric imaging technique that enables the simultaneous detection and imaging of the spatial distribution and relative abundance of different endogenous/exogenous compounds in biological samples. The excellent efficiency of MALDI-MSI is attributed to the choice of the MALDI matrix. However, to the best of our knowledge, no matrix has been specifically developed for AAs. Herein, we report a MALDI matrix, 2,5-dihydroxyterephthalic acid (DHT), which can improve the detection and imaging of AAs in biological samples by MALDI-MS. Our results indicated that DHT exhibited strong ultraviolet-visible (UV-vis) absorption, uniform matrix deposition, and high vacuum stability. Moreover, the matrix-related ion signals produced from DHT were reduced by 50 and 71.8% at m/z < 500 compared to the commonly used matrices of 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA), respectively, in their respective organic solvents. In terms of quantitative performance, arginine, glutamic acid, glutamine, and proline can be detected with limits of detection of 6, 4, 6, and 4 ng/mL, respectively, using the DHT as the matrix. Using DHT as the matrix, all 20 protein AAs were successfully detected in human serum by MALDI-MS, whereas only 7 and 10 AAs were detected when DHB and CHCA matrices were used, respectively. Furthermore, 20 protein AAs and taurine were successfully detected and imaged in a section of edible Crassostrea gigas (oyster) tissue for the first time. Our study demonstrates that using DHT as a matrix can improve the detection and imaging of AAs in biological samples by MALDI-MS.

What's in a name? Characteristics of clinical biofilms

In vitro biofilms are communities of microbes with unique features compared to individual cells. Biofilms are commonly characterized by physical traits like size, adhesion, and a matrix made of extracellular substances. They display distinct phenotypic features, such as metabolic activity and antibiotic tolerance. However, the relative importance of these traits depends on the environment and bacterial species. Various mechanisms enable biofilm-associated bacteria to withstand antibiotics, including physical barriers, physiological adaptations, and changes in gene expression. Gene expression profiles in biofilms differ from individual cells but, there is little consensus among studies and so far, a 'biofilm signature transcriptome' has not been recognized. Additionally, the spatial and temporal variability within biofilms varies greatly depending on the system or environment. Despite all these variable conditions, which produce very diverse structures, they are all noted as biofilms. We discuss that clinical biofilms may differ from those grown in laboratories and found in the environment and discuss whether the characteristics that are commonly used to define and characterize biofilms have been shown in infectious biofilms. We emphasize that there is a need for a comprehensive understanding of the specific traits that are used to define bacteria in infections as clinical biofilms.

Antibacterial activity and mechanism of malondialdehyde against Staphylococcus xylosus and Lactiplantibacillus plantarum isolated from a traditional Chinese dry-cured fish

Malondialdehyde (MDA) is one of the most representative reactive carbonyl species (RCSs) produced by lipid oxidation in food. However, the inhibitory effect of MDA on microorganisms has received little attention. Thus, the aim of this study was to reveal the antibacterial mechanism of MDA on Staphylococcus xylosus and Lactiplantibacillus plantarum isolated from dry-cured fish. The results showed that the minimum inhibitory concentrations (MICs) of MDA on S. xylosus and L. plantarum were 90 μg/ml and 180 μg/ml, respectively. Time-kill curves indicated a concentration-dependent antibacterial activity of MDA. Moreover, cell wall damage, cell membrane depolarization, intracellular adenosine triphosphate (ATP) decline, Ca2+ and Mg2+ leakage, cell morphological destruction and alterations in intracellular biomolecules were observed, which indicated the negative influence of MDA on cell membrane and cellular homeostasis. This study demonstrated the potential antimicrobial properties of MDA and provided theoretical support for the scientific prevention and control of lipid oxidation and microbial contamination in food. This study demonstrated the potential antibacterial properties of MDA and further enriches theoretical studies on the effects of lipid oxidation on microorganisms.