Isolation of the antibiotic pseudopyronine B and SAR evaluation of C3/C6 alkyl analogs

Integration of Antimicrobials and Delivery Systems: Synergistic Antibiofilm Activity with Biodegradable Nanoemulsions Incorporating Pseudopyronine Analogs

Multi-drug-resistant (MDR) bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), pose a significant challenge in healthcare settings. Small molecule antimicrobials (SMAs) such as α-pyrones have shown promise as alternative treatments for MDR infections. However, the hydrophobic nature of many SMAs limits their solubility and efficacy in complex biological environments. In this study, we encapsulated pseudopyronine analogs (PAs) in biodegradable polymer nanoemulsions (BNEs) for efficient eradication of biofilms. We evaluated a series of PAs with varied alkyl chain lengths and examined their antimicrobial activity against Gram-positive pathogens (S. aureus, MRSA, and B. subtilis). The selected PA with the most potent antibiofilm activity was incorporated into BNEs for enhanced solubility and penetration into the EPS matrix (PA-BNEs). The antimicrobial efficacy of PA-BNEs was assessed against biofilms of Gram-positive strains. The BNEs facilitated the solubilization and effective delivery of the PA deep into the biofilm matrix, addressing the limitations of hydrophobic SMAs. Our findings demonstrated that the PA2 exhibited synergistic antibiofilm activity when it was loaded into nanoemulsions. This study presents a promising platform for addressing MDR infections by combining pseudopyronine analogs with antimicrobial biodegradable nanoemulsions, overcoming challenges associated with treating biofilm infections.

Experimental and Computational Studies on the Biotransformation of Pseudopyronines with Human Cytochrome P450 CYP4F2

The secondary metabolite pseudopyronine B, isolated from Pseudomonas mosselii P33, was biotransformed by human P450 enzymes, heterologously expressed in the fission yeast Schizosaccharomyces pombe. Small-scale studies confirmed that both CYP4F2 and CYP4F3A were capable of oxidizing the substrate, with the former achieving a higher yield. In larger-scale studies using CYP4F2, three new oxidation products were obtained, the structures of which were elucidated by UV-vis, 1D and 2D NMR, and HR-MS spectroscopy. These corresponded to hydroxylated, carboxylated, and ester derivatives (1-3) of pseudopyronine B, all of which had been oxidized exclusively at the ω-position of the C-6 alkyl chain. In silico homology modeling experiments highlighted key interactions between oxygen atoms of the pyrone ring and two serine residues and a histidine residue of CYP4F2, which hold the substrate in a suitable orientation for oxidation at the terminus of the C-6 alkyl chain. Additional modeling studies with all three pseudopyronines revealed that the seven-carbon alkyl chain of pseudopyronine B was the perfect length for oxidation, with the terminal carbon lying close to the heme iron. The antibacterial activity of the substrates and three oxidation products was also assessed, revealing that oxidation at the ω-position removes all antimicrobial activity. This study both increases the range of known substrates for human CYF4F2 and CYP4F3A enzymes and demonstrates their utility in producing additional natural product derivatives.

Antibacterial and Anti-Biofilm Activity of Pyrones from a Pseudomonas mosselii Strain

The emergence of drug resistant microbes over recent decades represents one of the greatest threats to human health; the resilience of many of these organisms can be attributed to their ability to produce biofilms. Natural products have played a crucial role in drug discovery, with microbial natural products in particular proving a rich and diverse source of antimicrobial agents. During antimicrobial activity screening, the strain Pseudomonas mosselii P33 was found to inhibit the growth of multiple pathogens. Following chemical investigation of this strain, pseudopyronines A-C were isolated as the main active principles, with all three pseudopyronines showing outstanding activity against Staphylococcus aureus. The analogue pseudopyronine C, which has not been well-characterized previously, displayed sub-micromolar activity against S. aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa. Moreover, the inhibitory abilities of the pseudopyronines against the biofilms of S. aureus were further studied. The results indicated all three pseudopyronines could directly reduce the growth of biofilm in both adhesion stage and maturation stage, displaying significant activity at micromolar concentrations.

Isolation, Whole-Genome Sequencing, and Annotation of Three Unclassified Antibiotic-Producing Bacteria, Enterobacter sp. Strain RIT 637, Pseudomonas sp. Strain RIT 778, and Deinococcus sp. Strain RIT 780

We report the isolation, whole-genome sequencing, and annotation of Enterobacter sp. strain RIT 637, Pseudomonas sp. strain RIT 778, and Deinococcus sp. strain RIT 780. Disk diffusion assays using spent medium demonstrated that all bacteria produced bactericidal compounds against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Staphylococcus aureus ATCC 25923.

Gold-catalyzed homo- and cross-annulation of alkynyl carboxylic acids: a facile access to substituted 4-hydroxy 2H-pyrones and total synthesis of pseudopyronine A

A Au(i)-catalyzed homo- and cross-annulation reaction of alkynyl carboxylic acids offering 3,6-disubstituted 4-hydroxy 2H-pyrones has been demonstrated. The reaction tolerates various substituted alkynyl carboxylic acids and moderate to good yields of α-pyrone scaffolds have been observed. Later, a gram-scale reaction of the acid and the total synthesis of the natural product pseudopyronine A have been carried out successfully.

Short chain α-pyrones capable of potentiating penicillin G against Pseudomonas aeruginosa

The dramatic increase in bacterial resistance over the past three decades has greatly reduced the effectiveness of nearly all clinical antibiotics, bringing infectious disease to the forefront as a dire threat to global health. To combat these infections, adjuvant therapies have emerged as a way to reactivate known antibiotics against resistant pathogens. Herein, we report the evaluation of simplified α-pyrone adjuvants capable of potentiating penicillin G against Pseudomonas aeruginosa, a Gram-negative pathogen whose multidrug-resistant strains have been labeled by the Centers for Disease Control and Prevention as a serious threat to public health.

Metabolites of the Anaerobic Degradation of n-Hexane by Denitrifying Betaproteobacterium Strain HxN1

The constitutions of seven metabolites formed during anaerobic degradation of n-hexane by the denitrifying betaproteobacterium strain HxN1 were elucidated by comparison of their GC and MS data with those of synthetic reference standards. The synthesis of 4-methyloctanoic acid derivatives was accomplished by the conversion of 2-methylhexanoyl chloride with Meldrum's acid. The β-oxoester was reduced with NaBH₄ , the hydroxy group was eliminated, and the double bond was displaced to yield the methyl esters of 4-methyl-3-oxooctanoate, 3-hydroxy-4-methyloctanoate, (E)-4-methyl-2-octenoate, and (E)- and (Z)-4-methyl-3-octenoate. The methyl esters of 2-methyl-3-oxohexanoate and 3-hydroxy-2-methylhexanoate were similarly prepared from butanoyl chloride and Meldrum's acid. However, methyl (E)-2-methyl-2-hexenoate was prepared by Horner-Wadsworth-Emmons reaction, followed by isomerization to methyl (E)-2-methyl-3-hexenoate. This investigation, with the exception of 4-methyl-3-oxooctanoate, which was not detectable in the cultures, completes the unambiguous identification of all intermediates of the anaerobic biodegradation of n-hexane to 2-methyl-3-oxohexanoyl coenzyme A (CoA), which is then thiolytically cleaved to butanoyl-CoA and propionyl-CoA; these two metabolites are further transformed according to established pathways.

Development of a Robust and Quantitative High-Throughput Screening Method for Antibiotic Production in Bacterial Libraries

Over the past 30 years, there has been a dramatic rise in the number of infections caused by multidrug-resistant bacteria, which have proliferated due to the misuse and overuse of antibiotics. Over this same time period, however, there has also been a decline in the number of antibiotics with novel mechanisms of action coming to market. Therefore, there is a growing need for an increase in the speed at which new antibiotics are discovered and developed. Natural products produced by bacteria have been and continue to be a robust source of novel antibiotics; however, new and complementary methods for screening large bacterial libraries for novel antibiotic production are needed due to the current agar methods being limited in scope, time consuming, and prone to error. Herein, we describe a rapid, robust, and quantitative high-throughput liquid culture screening method for antibiotic production by bacteria. This method has the ability to screen both mono- and coculture mixtures of bacteria in vitro and be adapted to other phenotypic natural product analyses. Over 260 bacterial species were screened in monoculture, and 38 and 34% were found to produce antibiotics capable of inhibition of Staphylococcus aureus or Escherichia coli, respectively, with 8 and 4% being classified as strong producers (≥30% growth inhibition), respectively. Bacteria found to not produce antibiotics in monoculture were also screened in coculture using an adaptation of this method. Of the more than 270 cocultures screened, 14 and 30% were found to produce antibiotics capable of inhibition of S. aureus or E. coli, respectively. Of those bacteria found to produce antibiotics in monoculture, 43 bacteria were subjected to 16S rRNA sequencing and found to be majority Pseudomonas (37%), Serratia (19%), and Bacillus (14%) bacteria, but two novel producers, Herbaspirillum and Kluyvera, were also found.