Biology subjects

Porwollik, S.

Publications and source records attributed to Porwollik, S..

4 recordsLinked to original sources

bioRxiv2026

Identification of genes promoting fitness of a plant-associated Salmonella Choleraesuis strain on alfalfa sprouts during cold storage

Consumption of sprouted seeds, such as alfalfa sprouts, has increased in recent years due to their perceived health benefits. However, these food products have repeatedly been associated with outbreaks of foodborne pathogens, including Salmonella enterica serovars. An S. enterica serovar Choleraesuis strain previously isolated from melon fruit internal tissues was selected as a model to explore plant-pathogen interactions on alfalfa sprouts. Using this strain, we generated a barcoded transposon mutant library comprising approximately 33,000 unique insertions. This library and a collection of individual insertion mutants derived from it were used to identify genetic mechanisms contributing to the fitness of this S. Choleraesuis strain on alfalfa sprouts. The library was screened on sprouts during cold storage at 8{degrees}C. Negative selection for mutants with insertions in eda, fabF, lpp1_2, pnp, stpA, SCHChr_03621 and two intergenic regions were identified. Competition experiments between individual insertion mutants and the wild type confirmed the phenotype of three genes: eda, coding for a keto-hydroxyglutarate-aldolase/keto-deoxy-phosphogluconate aldolase involved in the Entner-Doudoroff pathway, mnmG, encoding the glucose-inhibited division protein, and fabF, involved in fatty acid biogenesis. This study offers a genome-wide perspective on the genes enabling a plant-associated Salmonella strain to persist on alfalfa sprouts. We highlight factors that are critical not only for persistence throughout the entire cold-storage period under conditions that closely simulate real shelf-life conditions in this high-risk food matrix.

microbiology↗

bioRxiv2025

Genomic factors contributing to the resilience of Salmonella enterica on ready-to-eat muskmelon

Salmonella outbreaks have repeatedly been associated with muskmelons. To identify genes under selection in S. enterica growing in this food matrix, barcoded transposon mutant libraries in three S. enterica serovars - Typhimurium, Enteritidis, and Newport - were screened for survival and growth on muskmelon. Applying stringent thresholds, a total of 26 genes in Typhimurium, 34 in Enteritidis, and 50 in Newport were found to significantly influence fitness during muskmelon interaction, with many of these being temperature dependent. Genes whose disruption affected fitness across all three serovars were enriched for functions related to RNA degradation and ribosome biogenesis. Targeted competition assays confirmed the contribution of selected genes, revealing nutrient-dependent phenotypes for most mutants. Remarkably, the polyribonucleotide nucleotidyltransferase gene, pnp, and the D-3-phosphoglycerate dehydrogenase gene, serA, conferred a selective advantage when growing in muskmelon but not under nutrition-rich control conditions. In contrast, the nitrogen regulation response regulator GlnG provided a muskmelon-specific fitness disadvantage. This study provides novel insights into genome-wide adaptation mechanisms of multiple Salmonella serovars to growth on muskmelons, revealing both shared and serovar-specific determinants while illustrating the dynamic genetic responses of S. enterica throughout the interaction period.

genomics↗

bioRxiv2023

Byproducts of inflammatory radical metabolism provide transient nutrient niches for microbes in the inflamed gut

Louis Pasteurs experiments on tartaric acid laid the foundation for our understanding of molecular chirality, but major questions remain. By comparing the optical activity of naturally-occurring tartaric acid with chemically-synthesized paratartaric acid, Pasteur realized that naturally-occurring tartaric acid contained only L-tartaric acid while paratartaric acid consisted of a racemic mixture of D- and L-tartaric acid. Curiously, D-tartaric acid has no known natural source, yet several gut bacteria specifically degrade D-tartaric acid. Here, we investigated the oxidation of monosaccharides by inflammatory reactive oxygen and nitrogen species. We found that this reaction yields an array of alpha hydroxy carboxylic acids, including tartaric acid isomers. Utilization of inflammation- derived D- and L-tartaric acid enhanced colonization by Salmonella Typhimurium and E. coli in murine models of gut inflammation. Our findings suggest that byproducts of inflammatory radical metabolism, such as tartrate and other alpha hydroxy carboxylic acids, create transient nutrient niches for enteric pathogens and other potentially harmful bacteria. Furthermore, this work illustrates that inflammatory radicals generate a zoo of molecules, some of which may erroneously presumed to be xenobiotics.

microbiology↗

bioRxiv2018

A macrophage-based screen identifies antibacterial compounds selective for intracellular Salmonella Typhimurium

Salmonella Typhimurium (S. Tm) evades the innate immune response by residing within host phagocytes. To identify inhibitors of intracellular S. Tm growth, we performed parallel chemical screens against S. Tm growing in macrophage-mimicking media and within macrophages. These screens identified novel antibacterials, and revealed that antibiotics with limited Gram-negative coverage are active against intracellular S. Tm. Screening of a S. Tm deletion library in the presence of one compound, metergoline, revealed that outer membrane perturbation enhanced activity in vitro. Combined with our observation of atypical cell surface characteristics of intracellular S. Tm, our work indicates that the bacterial outer membrane is permeabilized within macrophages. We show that metergoline targets the bacterial cytoplasmic membrane, and prolongs animal survival during a systemic S. Tm infection. This work highlights the predictive nature of intracellular screens for in vivo efficacy, and uncovers new aspects of bacterial physiology of intracellular S. Tm.

microbiology↗