Enzymatic Activity and Its Relationship with Organic Matter Characterization and Ecotoxicity to Aliivibrio fischeri of Soil Samples Exposed to Tetrabutylphosphonium Bromide

Unveiling the Behavior of an Endangered Facultative Cuprophyte Coincya Species in an Abandoned Copper Mine (Southeast Portugal)

Plant-soil interactions of endangered species with a high-priority conservation status are important to define in situ and ex situ conservation and restoration projects. The threatened endemic Coincya transtagana, thriving in the southwest of the Iberian Peninsula, can grow in metalliferous soils. The main goal of this study was to investigate the behavior of this species in soils rich in potentially toxic elements in the abandoned Aparis Cu mine. Soil samples were characterized for physicochemical properties and multielemental composition, as well as biological activity, through an analysis of enzymatic activities. Plant biomass was assessed, and multielemental analysis of the plants was also performed. The mine soils had slightly basic pH values and were non-saline and poor in mineral N-NH4, with medium-to-high organic matter concentration and medium cation-exchange capacity. In these soils, dehydrogenase had the highest activity, whereas protease had the lowest activity. The total concentrations of Cu (1.3-5.9 g/kg) and As (37.9-118 mg/kg) in soils were very high, and the available fraction of Cu in the soil also had high concentration values (49-491 mg/kg). Moreover, this study shows for the first time that C. transtagana had high uptake and translocation capacities from roots to shoots for Cu, Ni, and Cr. Although Cu in the plants' aerial parts (40-286 mg/kg) was considered excessive/toxic, no signs of plant toxicity disorders or P uptake reduction were detected. This preliminary study revealed that C. transtagana is Cu-tolerant, and it could be used for phytoremediation of soils contaminated with potentially toxic elements, while also contributing to its conservation.

Synthesized Bis-Triphenyl Phosphonium-Based Nano Vesicles Have Potent and Selective Antibacterial Effects on Several Clinically Relevant Superbugs

The increasing emergence of multidrug-resistant (MDR) pathogens due to antibiotic misuse translates into obstinate infections with high morbidity and high-cost hospitalizations. To oppose these MDR superbugs, new antimicrobial options are necessary. Although both quaternary ammonium salts (QASs) and phosphonium salts (QPSs) possess antimicrobial effects, QPSs have been studied to a lesser extent. Recently, we successfully reported the bacteriostatic and cytotoxic effects of a triphenyl phosphonium salt against MDR isolates of the Enterococcus and Staphylococcus genera. Here, aiming at finding new antibacterial devices possibly active toward a broader spectrum of clinically relevant bacteria responsible for severe human infections, we synthesized a water-soluble, sterically hindered quaternary phosphonium salt (BPPB). It encompasses two triphenyl phosphonium groups linked by a C12 alkyl chain, thus embodying the characteristics of molecules known as bola-amphiphiles. BPPB was characterized by ATR-FTIR, NMR, and UV spectroscopy, FIA-MS (ESI), elemental analysis, and potentiometric titrations. Optical and DLS analyses evidenced BPPB tendency to self-forming spherical vesicles of 45 nm (DLS) in dilute solution, tending to form larger aggregates in concentrate solution (DLS and optical microscope), having a positive zeta potential (+18 mV). The antibacterial effects of BPPB were, for the first time, assessed against fifty clinical isolates of both Gram-positive and Gram-negative species. Excellent antibacterial effects were observed for all strains tested, involving all the most concerning species included in ESKAPE bacteria. The lowest MICs were 0.250 µg/mL, while the highest ones (32 µg/mL) were observed for MDR Gram-negative metallo-β-lactamase-producing bacteria and/or species resistant also to colistin, carbapenems, cefiderocol, and therefore intractable with currently available antibiotics. Moreover, when administered to HepG2 human hepatic and Cos-7 monkey kidney cell lines, BPPB showed selectivity indices > 10 for all Gram-positive isolates and for clinically relevant Gram-negative superbugs such as those of E. coli species, thus being very promising for clinical development.

Sterically Hindered Quaternary Phosphonium Salts (QPSs): Antimicrobial Activity and Hemolytic and Cytotoxic Properties

Structure-activity relationships are important for the design of biocides and sanitizers. During the spread of resistant strains of pathogenic microbes, insights into the correlation between structure and activity become especially significant. The most commonly used biocides are nitrogen-containing compounds; the phosphorus-containing ones have been studied to a lesser extent. In the present study, a broad range of sterically hindered quaternary phosphonium salts (QPSs) based on tri-tert-butylphosphine was tested for their activity against Gram-positive (Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria and fungi (Candida albicans, Trichophyton mentagrophytes var. gypseum). The cation structure was confirmed to determine their biological activity. A number of QPSs not only exhibit high activity against both Gram-positive and -negative bacteria but also possess antifungal properties. Additionally, the hemolytic and cytotoxic properties of QPSs were determined using blood and a normal liver cell line, respectively. The results show that tri-tert-butyl(n-dodecyl)phosphonium and tri-tert-butyl(n-tridecyl)phosphonium bromides exhibit both low cytotoxicity against normal human cells and high antimicrobial activity against bacteria, including methicillin-resistant strains S. aureus (MRSA). The mechanism of QPS action on microbes is discussed. Due to their high selectivity for pathogens, sterically hindered QPSs could serve as effective tunable biocides.