Batch-mode degradation of high-strength phenolic pollutants by Pseudomonas aeruginosa strain STV1713 immobilized on single and hybrid matrices.

Controlled environments are pivotal in all bioconversion processes, influencing the efficacy of biocatalysts. In this study, we designed a batch bioreactor system with a packed immobilization column and a decontamination chamber to enhance phenol and 2,4-dichlorophenol degradation using the hyper-tolerant bacterium Pseudomonas aeruginosa STV1713. When free cells were employed to degrade phenol and 2,4-DCP at a concentration of 1000 mg/L, the cells completely removed the pollutants within 28 h and 66 h, respectively. Simultaneous reductions in chemical oxygen demand and biological oxygen demand were observed (phenol: 30.21 mg/L/h and 16.92 mg/L/h, respectively; 2,4-dichlorophenol: 12.85 mg/L/h and 7.21 mg/L/h, respectively). After assessing the degradation capabilities, the bacterium was immobilized on various matrices (sodium alginate, alginate-chitosan-alginate and polyvinyl alcohol-alginate) to enhance pollutant removal. Hybrid immobilized cells exhibited greater tolerance and degradation capabilities than those immobilized in a single matrix. Among them, polyvinyl alcohol-alginate immobilized cells displayed the highest degradation capacities (up to 2000 mg/L for phenol and 2500 mg/L for 2,4-dichlorophenol). Morphological analysis of the immobilized cells revealed enhanced cell preservation in hybrid matrices. Furthermore, the elucidation of the metabolic pathway through the catechol dioxygenase enzyme assay indicated higher activity of the catechol 1,2-dioxygenase enzyme, suggesting that the bacterium employed an ortho-degradation mechanism for pollutant removal. Additionally, enzyme zymography confirmed the presence of catechol 1,2-dioxygenase, with the molecular weight of the enzyme determined as 245 kDa.

Identification of 4-diphenylamino 3-iodo coumarin as a potent inhibitor of DNA gyrase B of S. aureus.

A necessity of therapeutics against antibiotic-resistant bacteria has led to a search for novel antibacterial compounds. The strategy to isolate compounds from non-microbial sources is the key to prevent antibiotic resistance. Here, we report isolation and characterization of an antibacterial coumarin derivative, 4-diphenylamino 3-iodo coumarin (4-DPA3IC) from a traditional drug formulation. The compound elicited high activity against MDR strains of S. aureus. Targets were identified through computational methods encompassing modules of Schrodinger 10.4. The 4-DPA3IC targeted S. aureus DNA gyrase enzyme B subunit. Amino acid residues and interactions involved here are totally different from those of novobiocin and clorobiocin. The validation was done by in vitro DNA gyrase supercoiling inhibition assay. This study proved 4-DPA3IC could potentially act against novobiocin and cholorbiocin resistant strains of S. aureus. Thus, the 4-DPA3IC is a unique inhibitor of bacterial DNA gyrase due to its plant origin as compared to other reported inhibitors.

Water-Chloroform Interface Assisted Microstructure Tuning of Polypyrrole-Silver Sheets.

The liquid-liquid interface of two immiscible solvents remarkably controls the morphology of polymeric nanostructures as compared to the polymerization in single solvent systems. The polymerization of pyrrole in the water-chloroform medium using silver nitrate (AgNO3) as oxidant yields polypyrrole/silver (PPy/Ag) sheets. The water-chloroform interface acts as a template for the growth of PPy/Ag hybrids into sheets by preventing the secondary growth of silver associated pyrrole oligomers in a three-dimensional (3-D) manner. On the contrary, the 3-D growth of pyrrole oligomers into spherical shapes at the water-chloroform interface is observed when ammonium persulfate (APS) is used as the oxidant. Transmission electron microscopic and scanning electron microscopic images reveal the sheetlike morphology of PPy/Ag with a relatively uniform distribution of Ag NPs (∼100 nm) on PPy sheets. The ratio of aqueous-organic bisolvent and the concentration/type of oxidant have a distinct effect on morphology, crystallinity, and electrical properties of PPy/Ag sheets. The dispersed PPy/Ag sheets are stable in moderately polar solvents up to 2 weeks. The electrochemical behavior of PPy/Ag sheets is confirmed by H2O2 sensing capability through cyclic voltammetry experiments. The antibacterial activity toward E. coli and S. aureus is quantitatively assessed using the minimum bactericidal concentration (MBC) determination.