We report a biodegradable fluorescent theranostic nanoprobe design strategy for simultaneous visualization and quantitative determination of antibacterial activity for the treatment of bacterial infections. Cationic-charged polycaprolactone (PCL) was tailor-made through ring-opening polymerization methodology, and it was self-assembled into well-defined tiny 5.0 ± 0.1 nm aqueous nanoparticles (NPs) having a zeta potential of +45 mV. Excellent bactericidal activity at 10.0 ng/mL concentration was accomplished in Gram-negative bacterium Escherichia coli (E. coli) while maintaining their nonhemolytic nature in mice red blood cells (RBC) and their nontoxic trend in wild-type mouse embryonic fibroblast cells with a selectivity index of >10 4 . Electron microscopic studies are evident of the E. coli membrane disruption mechanism by the cationic NP with respect to their high selectivity for antibacterial activity. Anionic biomarker 8-hydroxy-pyrene-1,3,6-trisulfonic acid (HPTS) was loaded in the cationic PCL NP via electrostatic interaction to yield a new fluorescent theranostic nanoprobe to accomplish both therapeutics and diagnostics together in a single nanosystem. The theranostic NP was readily degradable by a bacteria-secreted lipase enzyme as well as by lysosomal esterase enzymes at the intracellular compartments in <12 h and support their suitability for biomedical application. In the absence of bactericidal activity, the theranostic nanoprobe functions exclusively as a biomarker to exhibit strong greenfluorescent signals in live E. coli. Once it became active, the theranostic probe induces membrane disruption on E. coli, which enabled the costaining of nuclei by red fluorescent propidium iodide. As a result, live and dead bacteria could be visualized via green and orange signals (merging of red+green), respectively, during the course of the antibacterial activity by the theranostic probe. This has enabled the development of a new image-based fluorescence assay to directly visualize and quantitatively estimate the real-time antibacterial activity. Time-dependent bactericidal activity was coupled with selective photoexcitation in a confocal microscope to demonstrate the proof-of-concept of the working principle of a theranostic probe in E. coli. This new theranostic nanoprobe creates a new platform for the simultaneous probing and treating of bacterial infections in a single nanodesign, which is very useful for a longterm impact in healthcare applications.
Persulfides and polysulfides, collectively known as the sulfane sulfur pool along with hydrogen sulfide (H2S), play a central role in cellular physiology and disease. Exogenously enhancing these species in cells...
Vitamin B
1
(thiamin) is an essential nutrient for cellular metabolism. Microorganisms that are unable to synthesize thiamin either fully or in part exogenously obtain it from their environment or via exchanges with other microbial members in their community.
Microbial communities occupy diverse niches in nature, and exchanges of metabolites such as carbon sources, amino acids, and vitamins occur routinely among the community members. While large-scale metagenomic and metabolomic studies shed some light on these exchanges, the contribution of individual species and the molecular details of specific interactions are difficult to track. Here, we explore the molecular picture of vitamin B1 (thiamin) metabolism occurring in synthetic communities of Escherichia coli thiamin auxotrophs which engage in the exchange of thiamin and its biosynthesis intermediates. In E. coli, the two parts of thiamin - the 4-amino-5-hydroxymethyl-2-methylpyrimidine and the 4-methyl-5-(2-hydroxyethyl)thiazole - are synthesized by separate pathways using enzymes ThiC and ThiG, respectively, and are then joined by ThiE to form thiamin. We observed that even though E. coliΔthiC, ΔthiE, and ΔthiG mutants are thiamin auxotrophs, co-cultures of ΔthiC-ΔthiE and ΔthiC-ΔthiG grow in a thiamin-deficient minimal medium, whereas the ΔthiE-ΔthiG co-culture does not. Analysis of the exchange of thiamin and its intermediates in Vibrio anguillarum co-cultures, and in mixed co-cultures of V. anguillarum and E. coli revealed that the general pattern of thiamin metabolism and exchange among microbes is conserved across species. Specifically, the microorganisms exchange HMP and thiamin easily among themselves but not THZ. Furthermore, we observe that the availability of exogenous thiamin in the media affects whether these strains interact with each other or grow independently. This underscores the importance of the exchange of essential metabolites as a defining factor in building and modulating synthetic or natural microbial communities.
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