Alisha Aagesen | University of Minnesota - Twin Cities (original) (raw)

Papers by Alisha Aagesen

Journal of Bacteriology

The Na+ - ion translocating NADH:quinone oxidoreductase (NQR) from Vibrio cholerae is a membrane ... more The Na+ - ion translocating NADH:quinone oxidoreductase (NQR) from Vibrio cholerae is a membrane bound respiratory enzyme which harbors flavins and Fe-S clusters as redox centers. The NQR is the main producer of sodium motive force (SMF) and drives energy-dissipating processes such as flagellar rotation, substrate uptake, ATP synthesis and cation-proton antiport. The NQR requires for its maturation besides the six structural genes, nqrABCDEF, a flavin attachment gene encoded by apbE and the nqrM gene, presumably a Fe delivery protein. We here describe growth studies and quantitative real time PCR for the V. cholerae O395N1 strain wildtype (wt) and its mutant strains, Δnqr and ΔubiC, impaired in respiration. In a comparative proteome analysis, FeoB, the membrane subunit of the uptake system for Fe2+ (Feo), was increased in V. cholerae Δnqr. In this study, the upregulation is confirmed on the mRNA level, and results in improved growth rates of V. cholerae Δnqr with Fe2+ as iron source...

mBio, Jul 11, 2017

The Mycobacterium tuberculosis phosphate-specific transport (Pst) system controls gene expression... more The Mycobacterium tuberculosis phosphate-specific transport (Pst) system controls gene expression in response to phosphate availability by inhibiting the activation of the SenX3-RegX3 two-component system under phosphate-rich conditions, but the mechanism of communication between these systems is unknown. In Escherichia coli, inhibition of the two-component system PhoR-PhoB under phosphate-rich conditions requires both the Pst system and PhoU, a putative adaptor protein. E. coli PhoU is also involved in the formation of persisters, a subpopulation of phenotypically antibiotic-tolerant bacteria. M. tuberculosis encodes two PhoU orthologs, PhoY1 and PhoY2. We generated phoY single- and double-deletion mutants and examined the expression of RegX3-regulated genes by quantitative reverse transcription-PCR (qRT-PCR). Gene expression was increased only in the ΔphoY1 ΔphoY2 double mutant and could be restored to the wild-type level by complementation with either phoY1 or phoY2 or by deletio...

Microbiology (Reading, England), Dec 1, 2016

To examine the possible physiological significance of Mrp, a multi-subunit cation/proton antiport... more To examine the possible physiological significance of Mrp, a multi-subunit cation/proton antiporter from Vibrio cholerae, a chromosomal deletion Δmrp of V. cholerae was constructed and characterized. The resulting mutant showed a consistent early growth defect in LB broth that became more evident at elevated pH of the growth medium and increasing Na+ or K+ loads. After 24 h incubation, these differences disappeared likely due to the concerted effort of other cation pumps in the mrp mutant. Phenotype MicroArray analyses revealed an unexpected systematic defect in nitrogen utilization in the Δmrp mutant that was complemented by using the mrpA'-F operon on an arabinose-inducible expression vector. Deletion of the mrp operon also led to hypermotility, observable on LB and M9 semi-solid agar. Surprisingly, Δmrp mutation resulted in wild-type biofilm formation in M9 despite a growth defect but the reverse was true in LB. Furthermore, the Δmrp strain exhibited higher susceptibility to ...

Plos One, May 8, 2014

The Na + translocating NADH:quinone oxidoreductase (Na +-NQR) is a unique respiratory enzyme cata... more The Na + translocating NADH:quinone oxidoreductase (Na +-NQR) is a unique respiratory enzyme catalyzing the electron transfer from NADH to quinone coupled with the translocation of sodium ions across the membrane. Typically, Vibrio spp., including Vibrio cholerae, have this enzyme but lack the proton-pumping NADH:ubiquinone oxidoreductase (Complex I). Thus, Na +-NQR should significantly contribute to multiple aspects of V. cholerae physiology; however, no detailed characterization of this aspect has been reported so far. In this study, we broadly investigated the effects of loss of Na +-NQR on V. cholerae physiology by using Phenotype Microarray (Biolog), transcriptome and metabolomics analyses. We found that the V. cholerae DnqrA-F mutant showed multiple defects in metabolism detected by Phenotype Microarray. Transcriptome analysis revealed that the V. cholerae DnqrA-F mutant up-regulates 31 genes and down-regulates 55 genes in both early and mid-growth phases. The most up-regulated genes included the cadA and cadB genes, encoding a lysine decarboxylase and a lysine/cadaverine antiporter, respectively. Increased CadAB activity was further suggested by the metabolomics analysis. The down-regulated genes include sialic acid catabolism genes. Metabolomic analysis also suggested increased reductive pathway of TCA cycle and decreased purine metabolism in the V. cholerae DnqrA-F mutant. Lack of Na +-NQR did not affect any of the Na + pumping-related phenotypes of V. cholerae suggesting that other secondary Na + pump(s) can compensate for Na + pumping activity of Na +-NQR. Overall, our study provides important insights into the contribution of Na +-NQR to V. cholerae physiology.

Infection and immunity, Jan 28, 2015

Mycobacterium tuberculosis requires the phosphate-sensing signal transduction system Pst/SenX3-Re... more Mycobacterium tuberculosis requires the phosphate-sensing signal transduction system Pst/SenX3-RegX3 to resist host immune responses. A ΔpstA1 mutant lacking a Pst phosphate uptake system component is hyper-sensitive to diverse stress conditions in vitro and is attenuated in vivo due to constitutive expression of the phosphate starvation responsive RegX3 regulon. Transcriptional profiling of the ΔpstA1 mutant revealed aberrant expression of certain pe and ppe genes. PE and PPE proteins, defined by conserved N-terminal domains containing Pro-Glu (PE) or Pro-Pro-Glu (PPE) motifs, account for a substantial fraction of the M. tuberculosis genome coding capacity, but their functions are largely uncharacterized. Because some PE and PPE proteins localize to the cell wall, we hypothesized that over-expression of these proteins might sensitize M. tuberculosis to stress by altering cell wall integrity. To test this idea, we deleted pe and ppe genes that were over-expressed by ΔpstA1 bacteria....

Microbial Ecology, 2012

Bacterial surface structures called pili have been studied extensively for their role as possible... more Bacterial surface structures called pili have been studied extensively for their role as possible colonization factors. Most sequenced Vibrio genomes predict a variety of pili genes in these organisms, including several types of type IV pili. In particular, the mannose-sensitive hemagglutinin (MSHA) and the PilA pili, also known as the chitin-regulated pilus (ChiRP), are type IVa pili commonly found in Vibrio genomes and have been shown to play a role in the colonization of Vibrio species in the environment and/or host tissue. Here, we report sequence comparisons of two type IVa pilin subunit genes, mshA and pilA, and their corresponding amino acid sequences, for several strains from the three main human pathogenic Vibrio species, V. cholerae, V. parahaemolyticus, and V. vulnificus. We identified specific groupings of these two genes in V. cholerae, whereas V. parahaemolyticus and V. vulnificus strains had no apparent allelic clusters, and these genes were strikingly divergent. These results were compared with other genes from the MSHA and PilA operons as well as another Vibrio pili from the type IVb group, the toxin co-regulated pilus (TCP) from V. cholerae. Our data suggest that a selective pressure exists to cause these strains to vary their MSHA and PilA pilin subunits. Interestingly, V. cholerae strains possessing TCP have the same allele for both mshA and pilA. In contrast, V. cholerae isolates without TCP have polymorphisms in their mshA and pilA sequences similar to what was observed for both V. parahaemolyticus and V. vulnificus. This data suggests a possible linkage between host interactions and maintaining a highly conserved type IV pili sequence in V. cholerae. Although the mechanism underlying this intriguing diversity has yet to be elucidated, our analyses are an important first step towards gaining insights into the various aspects of Vibrio ecology.

Applied and Environmental Microbiology, 2013

Vibrio parahaemolyticus can resist oyster depuration, suggesting that it possesses specific facto... more Vibrio parahaemolyticus can resist oyster depuration, suggesting that it possesses specific factors for persistence. We show that type I pili, type IV pili, and both flagellar systems contribute to V. parahaemolyticus persistence in Pacific oysters whereas type III secretion systems and phase variation do not. a The log mean or log reduction and standard error are shown. Different letters indicate statistical significance for each time point according to the one-way ANOVA (treatment) and post hoc comparisons using Tukey's HSD test (P Ͻ 0.05). These data represent four independent experiments with 12 animals analyzed at each time point. May 2013 Volume 79 Number 10 Applied and Environmental Microbiology p. 3303-3305 aem.asm.org 3303 on June 11, 2014 by guest http://aem.asm.org/ Downloaded from a The log mean or log reduction and standard error are shown. Different letters indicate statistical significance for each time point according to the one-way ANOVA (treatment) and post hoc comparisons using Tukey's HSD test (P Ͻ 0.05). These data represent four replicate experiments with 15 animals analyzed for each time point.

Food Microbiology, 2014

During the warmer summer months, oysters are conditioned to spawn, resulting in massive physiolog... more During the warmer summer months, oysters are conditioned to spawn, resulting in massive physiological efforts for gamete production. Moreover, the higher temperatures during the summer typically result in increased bacteria populations in oysters. We hypothesized that these animals are under multiple stresses that lead to possible immune system impairments during the summer months that can possibly lead to death. Here we show that in the summer and the fall animals exposed to a short heat stress respond similarly, resulting in a general trend of more bacteria being found in heat shocked animals than their non-heat shocked counterparts. We also show that naturally occurring bacterial populations are effected by a heat shock. In addition, oysters artificially contaminated with Vibrio parahaemolyticus were also affected by a heat shock. Heat shocked animals contained higher concentrations of V. parahaemolyticus in their tissues and hemolymph than control animals and this was consistent for animals examined during summer and fall. Finally, oyster hemocyte interactions with V. parahaemolyticus differed based on the time of the year. Overall, these findings demonstrate that seasonal changes and/or a short heat shock is sufficient to impact bacterial retention, particularly V. parahaemolyticus, in oysters and this line of research might lead to important considerations for animal harvesting procedures.