2019 Mississippi IDeA Conference

Yetunde Adewunmi¹, Sanchirmaa Namjilsuren¹, Dahlia Amato², Douglas Amato², William Walker², Olga Mavrodi¹, Derek Patton², and Dmitri Mavrodi¹

¹School of Biological, Environmental, and Earth Sciences, The University of Southern Mississippi, Hattiesburg, MS

²School of Polymer Science and Engineering, The University of Southern Mississippi, Hattiesburg, MS

Plant-derived aldehydes are constituents of essential oils (EOs) that possess broad range antimicrobial activity and kill microorganisms without promoting resistance. However, their widespread use is hampered by chemical instability and knowledge gaps in their mode of action (MOA). To circumvent these issues, we incorporated 4-methoxybenzaldehyde from star anise into a polymer network via acetal linkages called PANDAs (Pro-Antimicrobial Networks via Degradable Acetals). The resultant antimicrobial polymer released 4-methoxybenzaldehyde upon a change in pH and humidity and controlled growth of the multi-drug resistant pathogen Pseudomonas aeruginosa PAO1. To identify cellular pathways targeted by PANDAs, we generated 10,000 transposon mutants of PAO1 and screened them for hypersensitivity to 4-methoxybenzaldehyde. The screen yielded 27 unique mutants defective in components of RND efflux pumps, membrane transporters, porins, enzymes of the molybdenum cofactor biosynthesis complex, and hypothetical proteins. To further improve the antimicrobial efficacy of PANDAs, we combined 4-methoxybenzaldehyde with epigallocatechin gallate (EGCG), a green tea polyphenol that inhibits efflux in gram-positive and -negative bacteria. We found that EGCG acted synergistically with 4-methoxybenzaldehyde and significantly reduced its minimal inhibitory concentration. We then used RNA-seq to profile transcriptomic responses of P. aeruginosa to 4-methoxybenzaldehyde, EGCG, and their combination thereof. The response to 4-methoxybenzaldehyde involved a total of 256 genes, some of which encoded nitrate reductase, energy metabolism enzymes, transporters, and components of efflux pumps and type III secretion machinery. The exposure to EGCG altered expression of 28 genes involved in signal transduction, antioxidant defense, and carbohydrate metabolism. Finally, the synergistic interaction between 4-methoxybenzaldehyde and EGCG differentially affected components of efflux, membrane transport, stress response, and nitrate reductase pathways. Results of this study will help to elucidate cellular pathways targeted by EO constituents and produce novel phytoaldehyde-containing polymer materials that effectively kill pathogenic microorganisms.