Climate change significantly impacts plant growth by reducing the availability of essential nutrients, including phosphorus (P). As an alternative to chemical fertilizers, climate-smart agriculture should prioritize the use of beneficial microorganisms such as P-solubilizing bacteria (PSB). Here, we report the ability of the P1.5S strain of Bacillus safensis to solubilize P under the stress caused by different pH, temperature, and salinity. Genomic data and the TBLASTN algorithm were used to identify genes involved in stress tolerance and P solubilization. Stress tolerance was confirmed by cultivation under varying conditions, while the mechanism of P solubilization was investigated using HPLC. Bioinformatic analysis revealed at least 99 genes related to stress tolerance, 32 genes responsible for organic acids synthesis, as well as 10 genes involved in phosphatase production. B. safensis P1.5S can grow at 37 °C, high NaCl concentrations (15 g/L), and is tolerant of alkaline and acidic conditions. The P1.5S strain primarily solubilizes P by releasing organic acids, including lactic, acetic, and succinic acid. Our data revealed that the efficacy of P solubilization was not affected by abiotic stressors (19.54 µg P/mL). By evaluating the P solubilization ability of B. safensis P1.5S induced by stressors represented by varying pH, temperature, and salinity conditions, this work introduces a new avenue for increasing P availability, which enables and endorses the future development of practical applications of B. safensis P1.5S in challenging agricultural environments.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is considered the main cause of nosocomial and community-associated infections. Because of antimicrobial resistance, MRSA infections are difficult or impossible to treat, leading to high mortality rates and significant economic and societal costs. In view of the MRSA challenge to public health all over the world, the identification of new and effective anti-MRSA agents is a high medical priority. Objectives: A new series of tricyclic flavonoids with a methyl substituent on ring A of the flavonoid skeleton was synthesized to assess their antimicrobial properties. Methods: The structures of novel synthetic tricyclic flavonoids and their 3-dithiocarbamic flavanones were proven by X-ray structural analyses. Minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC) were used to evaluate antimicrobial activity. Growth kinetic and time–kill assays were employed to confirm the antibacterial effectiveness. The mechanism of action was investigated using fluorescence microscopy. Results: Our results show that the tricyclic flavonoids exhibited important antibacterial and antifungal activities, with MIC and MBC values as low as 1.95 µg/mL and 3.90 µg/mL recorded for compound 5e against a multidrug-resistant MRSA strain. Flavonoid 5e induced a more important bacteriostatic effect compared with chloramphenicol, inhibiting the bacterial growth for up to 24 h at concentrations equivalent to 2 × MIC. Also, 5e exhibited a significant bactericidal activity, with no viable cells evidenced after 6 h of incubation in the presence of MBC and a total kill effect recorded up to 24 h. The anti-MRSA activity may be explained by the cell membrane impairment induced by 5e. Conclusions: All the data support the idea that flavonoid 5e is a reliable candidate to develop effective anti-MRSA agents, but further studies are necessary.

The rapid emergence and spread of multidrug-resistant microorganisms is threatening our ability to treat common infections, with serious medical, social, and economic consequences. Despite substantial progress in the global fight against antibiotic resistance, the number of effective antibiotics is rapidly decreasing, underlying the urgent need to develop novel antimicrobials. In the present study, the green synthesis of novel iodine-substituted tricyclic flavonoids has been accomplished using an eco-friendly reagent, HPW-SiO₂, as a cyclization agent for the precursor 3-dithiocarmamic flavanones. In vitro antimicrobial activity of the new compounds was evaluated using minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentrations. All tested compounds displayed potent inhibitory activity against all tested microbial strains, with the lowest MIC values of 0.12 µg/mL and 0.48 µg/mL recorded for compound 5c against Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus. Higher MIC values (7.81 µg/mL) were registered for several flavonoids against Gram-negative bacteria Escherichia coli and Acinetobacter pittii. No inhibitory activity was evidenced against Pseudomonas aeruginosa strain. The highest antifungal activity was displayed by flavonoid 5d against Candida krusei (MIC = 3.9 µg/mL). The same compound also exhibited the most potent bactericidal and fungicidal activity against Bacillus subtilis (0.9 µg/mL) and Staphylococcus aureus (1.97 µg/mL), Candida albicans, and Candida krusei (7.81 µg/mL). Based on the reported results, we believe that the novel iodine-substituted tricyclic flavonoids have good potential to become new antimicrobial agents effective against bacterial and fungal strains, including WHO-priority pathogens.