2 research outputs found
Data_Sheet_1_Enhanced Bacterial Fitness Under Residual Fluoroquinolone Concentrations Is Associated With Increased Gene Expression in Wastewater-Derived qnr Plasmid-Harboring Strains.docx
<p>Plasmids harboring qnr genes confer resistance to low fluoroquinolone concentrations. These genes are of significant clinical, evolutionary and environmental importance, since they are widely distributed in a diverse array of natural and clinical environments. We previously extracted and sequenced a large (∼185 Kbp) qnrB-harboring plasmid, and several small (∼8 Kbp) qnrS-harboring plasmids, from Klebsiella pneumoniae isolates from municipal wastewater biosolids, and hypothesized that these plasmids provide host bacteria a selective advantage in wastewater treatment plants (WWTPs) that often contain residual concentrations of fluoroquinolones. The objectives of this study were therefore to determine the effect of residual fluoroquinolone concentrations on the growth kinetics of qnr plasmid-harboring bacteria; and on the copy number of qnr plasmids and expression of qnr genes. Electrotransformants harboring either one of the two types of plasmids could grow at ciprofloxacin concentrations exceeding 0.5 μg ml<sup>-1</sup>, but growth was significantly decreased at concentrations higher than 0.1 μg ml<sup>-1</sup>. In contrast, plasmid-free strains failed to grow even at 0.05 μg ml<sup>-1</sup>. No differences were observed in plasmid copy number under the tested ciprofloxacin concentrations, but qnr expression increased incrementally from 0 to 0.4 μg ml<sup>-1</sup>, suggesting that the transcription of this gene is regulated by antibiotic concentration. This study reveals that wastewater-derived qnr plasmids confer a selective advantage in the presence of residual fluoroquinolone concentrations and provides a mechanistic explanation for this phenomenon.</p
How Pulse Width Affects Laser Ablation of Organic Liquids
Laser synthesis in liquids is often
carried out in organic solvents
to prevent oxidation of metals during nanoparticle generation and
to produce tailored carbon-based nanomaterials. This work investigates
laser ablation of neat organic liquids acetone, ethanol, n-hexane, and toluene with pulse widths ranging from 30 fs to 4 ps
through measurements of reaction kinetics and characterization of
the ablation products with optical spectroscopy and mass spectrometry.
Increasing the pulse width from 30 fs to 4 ps impacts both the reaction
kinetics and product distributions, suppressing the formation of solvent
molecule dimers and oxidized molecules while enhancing the yields
of gaseous molecules, sp-hybridized carbons, and
fluorescent carbon dots. The observed trends are explained in the
context of established ionization mechanisms and cavitation bubble
dynamical processes that occur during ultrashort pulsed laser ablation
of liquid media. The results of this work have important implications
both for controlling the formation of carbon shells around metal nanoparticles
during the ablation of solid targets in liquid and producing carbon
nanomaterials directly from the ablation of organic liquids without
a solid target