Biology subjects

Olson, M. A.

Publications and source records attributed to Olson, M. A..

5 recordsLinked to original sources

bioRxiv2025

Opposing roles for iron transport systems in gallium tolerance in extraintestinal pathogenic Escherichia coli

Gallium is a promising antibacterial candidate because it displaces iron atoms inside bacterial cells but does not undergo redox cycling. It inhibits growth by disrupting essential iron-dependent processes. However, Escherichia coli are naturally less sensitive to gallium than many other bacteria, and the mechanisms that control gallium tolerance are not completely understood. We performed a genome-wide transposon sequencing (TnSeq) screen to identify genes important for the survival of an extraintestinal pathogenic E. coli isolate (M12) in gallium nitrate. The TnSeq results indicated that inactivation of enterobactin siderophore-related genes (entS, fepD, fes, fepB) enhances bacterial survival in gallium, while disrupting the ferric dicitrate transport system increases susceptibility. We validated these findings through targeted gene knockouts and gallium sensitivity experiments. Our findings suggest that enterobactin can complex with gallium for cellular uptake, but that the ferric citrate receptor FecA can discriminate between gallium citrate and iron citrate. Expression of fecA increased with gallium exposure, showing that gallium induces FecA-mediated iron uptake. Gallium also increased intracellular levels of manganese in the {Delta}fecA strain. Supplementation with iron or manganese restored growth of M12 {Delta}fecA in gallium, suggesting that gallium sensitivity is linked to both iron starvation and oxidative stress. As the ferric dicitrate transport system is an important virulence factor in several extraintestinal infection sites, our results suggest that targeting FecA may increase E. coli susceptibility to gallium while also suppressing virulence. ImportanceEscherichia coli extraintestinal infections that are resistant to traditional antibiotics are associated with more deaths than any other species. Gallium-based therapies may represent a non-antibiotic approach to treating extraintestinal pathogenic E. coli strains that affect both humans and animals. Our results are significant as they show that the enterobactin siderophore and the ferric dicitrate iron transport systems expressed by these bacteria have opposing roles in E. coli gallium sensitivity. These findings could be leveraged to enhance the efficacy of gallium therapeutics.

microbiology↗

bioRxiv2025

In situ light-driven pH modulation for NMR studies

Proton exchange is a fundamental chemical event, and NMR provides the most direct readout of protonation events with site-specific resolution. Conventional approaches require manual titration of sample pH to collect a series of NMR spectra at different pH values. This requires extensive sample handling and often results in significant sample loss, leading to reduced signal or the need to prepare additional samples. Here, we introduce a novel approach to control pH in NMR samples using water soluble photoacids, which alter the pH of the solution from near neutral to acidic pH upon in situ photo-illumination. We show that the solution pH can be precisely controlled by choice of illumination wavelength and intensity and sufficient protons are released from the photoacid to achieve meaningful pH change in samples where the molecule of interest has significant buffering capacity, such as a >100 M protein sample. The pH is monitored in situ using internal standards with pH-sensitive chemical shifts. This method enables precise, calibrated, non-invasive change of sample pH within an NMR magnet, dramatically reducing the necessary sample handling. These findings highlight the potential of light-induced pH control in NMR experiments and increase the robustness and reliability of pH-dependent studies. With pH playing a key role in modulating chemical behavior in both biological and synthetic systems, the ability to study protonation states and modulate sample pH in a simple and precise manner that is compatible with high-resolution NMR studies of molecular structure and function has wide applications. Entry for the Table of ContentsIn this work, we introduce a novel approach to control pH in NMR samples using light-activated photoacids. By combining light stimuli with pH-sensitive molecules, we demonstrate the ability to precisely modulate pH without physically manipulating the sample. This method enables non-invasive pH titration in NMR studies, where pH plays a key role in protein function. Our findings highlight the potential of light-induced pH control to overcome existing limitations in NMR, providing a powerful tool for advancing protein research under controlled pH conditions. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=75 SRC="FIGDIR/small/633412v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@1bf9839org.highwire.dtl.DTLVardef@1a2d77eorg.highwire.dtl.DTLVardef@1f1a68dorg.highwire.dtl.DTLVardef@1ed73fa_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Genes associated with fitness and disease severity in the pan-genome of mastitis-associated Escherichia coli

Bovine mastitis caused by Escherichia coli may manifest as subclinical through severe acute disease and can be transient or persistent in nature. Little is known about bacterial factors that impact clinical outcomes or allow some strains to outcompete others in the mammary gland (MG) environment. Mastitis-associated E. coli (MAEC) may have distinctive characteristics which may contribute to the varied nature of the disease. In this study, we sequenced the genomes of 96 MAEC strains isolated from cattle with clinical mastitis (CM). We utilized clinical severity data to perform genome-wide association studies to identify accessory genes associated with strains isolated from mild or severe CM, or with high or low competitive fitness during in vivo competition assays. Genes associated with pathogenic or commensal strains isolated from bovine and avian sources were also identified. A type-2 secretion system (T2SS) and a chitinase (ChiA) exported by this system were strongly associated with pathogenic isolates compared with commensal strains. Strains carrying these genes also had higher competitive fitness during experimental intramammary infections. Deletion of chiA from MAEC isolates decreased their adherence to cultured bovine mammary epithelial cells, suggesting that the increased fitness associated with strains possessing this gene may be due to better attachment in the MG. ImportanceBovine mastitis caused by MAEC compromises animal health and inflicts substantial product losses in dairy farming. Given their high levels of intraspecies genetic variability, virulence factors of commonly used MAEC model strains may not be relevant to all members of this group. Here we analyzed clinical data as well as fitness (quantified in a mouse MG model) of diverse MAEC isolates to identify accessory genes that contribute to infection. We demonstrated a novel role for chitinase in promoting attachment to mammary epithelial cells. Reverse genetic approaches can be applied to the collection of strains and their complete genome sequences that we have presented here. Overall, these results provide a much richer understanding of MAEC and suggest bacterial processes that may underlie the clinical diversity associated with mastitis and their adaptation to this unique environment.

microbiology↗

bioRxiv2022

Machine learning reveals conserved chromatin patterns determining meiotic recombination sites in plants

Distribution of meiotic recombination events in plants has been associated with local chromatin and DNA characteristics, chromosome landmark proximity, and other features1-7. However, relative importance of these characteristics is unclear and it is unknown if they are sufficient to unambiguously determine recombination landscape8. Here, we analyzed over 40 DNA sequence, chromatin, and chromosome location features of maize and Arabidopsis recombination sites using machine learning9,10. We discovered that a combination of just three features, CG methylation, CHG methylation, and nucleosome occupancy, enabled identification of exact crossover site with 90% accuracy. These results imply redundancy of most recombination site characteristics. Recombination takes place in a small fraction of the genome with chromatin features distinct from those of genome at large. Surprisingly, crossover sites show elevated heterochromatin histone marks despite low DNA methylation. Crossover site features show broad evolutionary conservation, which will enable creating genetic maps in species where conventional mapping is unfeasible.

plant biology↗

bioRxiv2020

A link between zinc uptake, bile salts, and a capsule required for virulence of a mastitis-associated extraintestinal pathogenic Escherichia coli strain

Extraintestinal pathogenic Escherichia coli (ExPEC) are major causes of urinary and bloodstream infections. ExPEC reservoirs are not completely understood. Some mastitis-associated E. coli (MAEC) strains carry genes associated with ExPEC virulence, including metal scavenging, immune avoidance, and host attachment functions. In this study, we investigated the role of the high-affinity zinc uptake (znuABC) system in the MAEC strain M12. Elimination of znuABC moderately decreased fitness during mouse mammary gland infections. The {Delta}znuABC mutant strain exhibited an unexpected growth delay in the presence of bile salts, which was alleviated by the addition of excess zinc. We isolated {Delta}znuABC mutant suppressor mutants with improved growth of in bile salts, several of which no longer produced the K96 capsule made by strain M12. Addition of bile salts also reduced capsule production by strain M12 and ExPEC strain CP9, suggesting that capsule synthesis may be detrimental when bile salts are present. To better understand the role of the capsule, we compared the virulence of mastitis strain M12 with its unencapsulated {Delta}kpsCS mutant in two models of ExPEC disease. The wild type strain successfully colonized mouse bladders and kidneys and was highly virulent in intraperitoneal infections. Conversely, the {Delta}kpsCS mutant was unable to colonize kidneys and was unable to cause sepsis. These results demonstrate that some MAEC may be capable of causing human ExPEC illness. Virulence of strain M12 in these infections is dependent on its capsule. However, capsule may interfere with zinc homeostasis in the presence of bile salts while in the digestive tract.

microbiology↗