Biology subjects

Kahl, L. J.

Publications and source records attributed to Kahl, L. J..

4 recordsLinked to original sources

bioRxiv2026

Fitness costs of antibiotic resistance mutations in rich media do not reliably predict those in infection-like environments

The acquisition of antibiotic resistance is typically associated with a fitness cost, reducing the competitive ability of cells in the absence of antibiotics. Our ability to predict these costs informs our ability to predict how likely it is that resistance will subside in the absence of treatment. Fitness costs are typically measured in laboratory cultures using a nutritionally rich medium for growth. Here, we tested the impact of infection-like environments on the prevalence and magnitude of fitness costs associated with antibiotic resistance mutations in the opportunistic pathogen Pseudomonas aeruginosa. We assessed two different clinically relevant infection niches, the lung and urinary tract, through the use of infection-niche mimicking media that models the chemical compositions of these niches. The fitness costs of resistance mutations in rich media did not reliably predict those in infection-like environments, on average costs were increased in the lung-mimicking environment and costly mutations were less prevalent in the urinary tract-mimicking environment. Synthetic human urine significantly enhanced the fitness of P. aeruginosa with resistance mutations in nfxB, encoding a multidrug efflux pump transcriptional repressor, and we identified oxalate as the likely component driving this effect. Our findings highlight the importance of environmental chemical composition for shaping the fitness costs of resistance in P. aeruginosa and suggest that nfxB mutants may have a selective advantage in the urinary tract, mediated by the presence of oxalate.

microbiology↗

bioRxiv2022

Light/dark and temperature cycling modulate metabolic electron flow in Pseudomonas aeruginosa biofilms

Sunlight drives phototrophic metabolism, which affects redox conditions and produces substrates for non-phototrophs. These environmental parameters fluctuate daily due to Earths rotation, and non-phototrophic organisms can therefore benefit from the ability to respond to, or even anticipate, such changes. Circadian rhythms, such as daily changes in body temperature, in host organisms can also affect local conditions for colonizing bacteria. Here, we investigated the effects of light/dark and temperature cycling on biofilms of the opportunistic pathogen Pseudomonas aeruginosa PA14. We grew biofilms in the presence of a respiratory indicator dye and found that greater dye reduction occurred in biofilm zones that formed during dark intervals and at lower temperatures. This pattern formation occurred with cycling of blue, red, or far-red light, and a screen of mutants representing potential sensory proteins identified two with defects in pattern formation, specifically under red light cycling. We also found that the physiological states of biofilm subzones formed under specific light and temperature conditions were retained during subsequent condition cycling. Light/dark and temperature cycling affected expression of genes involved in primary metabolic pathways and redox homeostasis, including those encoding electron transport chain components. Consistent with this, we found that cbb3-type oxidases contribute to dye reduction under light/dark cycling conditions. Together, our results indicate that cyclic changes in light exposure and temperature have lasting effects on redox metabolism in biofilms formed by a non-phototrophic, pathogenic bacterium. IMPORTANCEOrganisms that do not obtain energy from light can nevertheless be affected by daily changes in light exposure. Many aspects of animal and fungal physiology fluctuate in response to these changes, including body temperature and the activities of antioxidant and other redox enzymes that play roles in metabolism. Whether redox metabolism is affected by light/dark and temperature cycling in bacteria that colonize such circadian organisms has not been studied in detail. Here we show that growth under light/dark and temperature cycling leads to rhythmic changes in redox metabolism in Pseudomonas aeruginosa and identify proteins involved in this response. P. aeruginosa is a major cause of healthcare-associated infections and designated as a serious threat by the CDC due to its recalcitrance during treatments. Our findings have the potential to inform therapeutic strategies that incorporate controlled light exposure or consider P. aeruginosas responses to conditions in the host.

microbiology↗

bioRxiv2019

Light-mediated decreases in cyclic di-GMP levels are potentiated by pyocyanin and inhibit structure formation in Pseudomonas aeruginosa biofilms

Light is known to trigger regulatory responses in diverse organisms including slime molds, animals, plants, and phototrophic bacteria. However, light-dependent processes in non-phototrophic bacteria, and those of pathogens in particular, have received comparatively little research attention. In this study, we examined the impact of light on multicellular development in Pseudomonas aeruginosa, a leading cause of biofilm-based bacterial infections, using a colony morphology assay. In this assay, P. aeruginosa strain PA14 grown in the dark forms vertical structures (i.e., \"wrinkles\") on the third day of incubation. We found that growth in blue light inhibited wrinkle formation until the fifth day and that this required the phenazine pyocyanin, a redox-active metabolite produced by PA14. Light-dependent inhibition of wrinkling was also correlated with low levels of cyclic di-GMP (c-di-GMP), consistent with the role of this signal in stimulating biofilm matrix production. Though phenazine-null biofilms also showed lower levels of c-di-GMP and subtle effects on wrinkling when grown in the light, their overall levels of c-di-GMP were higher than those of the wild type. This indicates that phenazines and light simultaneously promote c-di-GMP degradation such that c-di-GMP is pushed to a minimum level, yielding a pronounced macroscopic phenotype. A screen of enzymes with the potential to catalyze c-di-GMP synthesis or degradation identified four proteins that contribute to light-dependent inhibition of biofilm wrinkling. Together, these results provide a foundation for understanding the significance of light-dependent regulation in P. aeruginosa.\n\nImportanceThe response to light in non-phototrophic bacteria (i.e., chemotrophs) is relatively understudied in comparison to light-mediated behavior in eukaryotes and phototrophic bacteria. Though they do not depend on light for growth, chemotrophic bacteria could benefit from sensing this cue when it correlates with other parameters that are important for metabolism. In this paper, we describe light-dependent effects on a cellular signal that controls the development of multicellular assemblages, called biofilms, in Pseudomonas aeruginosa. We found that light at intensities that are not harmful to human cells inhibited biofilm maturation. P. aeruginosa is a leading cause of chronic lung infections in people with cystic fibrosis and of hospital-acquired infections. As P. aeruginosas recalcitrance to treatment is attributed in part to its facile formation of biofilms, this study provides insight into a mechanism that could be inhibited via new therapeutic tools, such as photodynamic therapy.

microbiology↗

bioRxiv2019

Biofilm inhibitor taurolithocholic acid alters colony morphology, specialized metabolism, and virulence of Pseudomonas aeruginosa

Biofilm inhibition by exogenous molecules has been an attractive strategy for the development of novel therapeutics. We investigated the biofilm inhibitor taurolithocholic acid (TLCA) and its effects on the specialized metabolism, virulence and biofilm formation of the clinically relevant bacterium Pseudomonas aeruginosa strain PA14. Our study shows that TLCA alters specialized metabolism, thereby affecting P. aeruginosa colony biofilm physiology. We observed an upregulation of metabolites correlated to virulence such as the siderophore pyochelin. A wax moth virulence assay confirmed that treatment with TLCA increases virulence of P. aeruginosa. Based on our results, we believe that future endeavors to identify biofilm inhibitors must consider how a putative lead is altering the specialized metabolism of a bacterial community to prevent pathogens from entering a highly virulent state.

microbiology↗