Biology subjects

Krishnamurthi, V. R.

Publications and source records attributed to Krishnamurthi, V. R..

3 recordsLinked to original sources

bioRxiv2020

Microampere electric currents caused bacterial membrane damage and two-way leakage in short time

Physical agents such as low electric voltages and currents have recently gained attention for antimicrobial treatment due to their bactericidal capability. Although microampere electric currents were shown to suppress the growth of bacteria, it remains unclear to what extent the microampere currents damage bacterial membrane. Here, we investigated the membrane damage and two-way leakage caused by microampere electric currents ([≤] 100 A) in a short time (30 min). Based on MitoTracker staining, propidium iodide staining, filtration assays, and quantitative single-molecule localization microscopy, we found that microampere electric currents caused significant membrane damages and allowed two-way leakages of ions, small molecules and proteins. This study paves the way to new development and antibiotic applications of ultra-low electric voltages and currents. Statement of SignificancePrevious studies showed that treating bacteria with milliampere electric currents for 72 hours led to significant damages of the bacterial membrane. However, it remains unclear to what extent membrane damages and two-way (i.e. inward and outward) leakages are caused by lower electric currents in a shorter time. In this work, we set out to answer this question. We carried out several assays on the bacteria treated by microampere electric currents of [≤] 100 A for 30 min, including MitoTracker staining, propidium iodide staining, filtration assays, and quantitative single-molecule localization microscopy. We found and quantified that the membrane damages were caused by microampere electric currents in half an hour and allowed two-way leakages of ions, small molecules, and proteins.

biophysics↗

bioRxiv2020

Antimicrobial silver inhibits bacterial movement and stalls flagellar motor

Silver (Ag) has been gaining broad attention due to their antimicrobial activities and the increasing resistance of bacteria to commonly prescribed antibiotics. However, various aspects of the antimicrobial mechanism of Ag have not been understood, including how silver affects the motility of bacteria, a factor that is intimately related to bacterial virulence. Here we report our study on the antibiotic effects of Ag+ ions on the motility of E. coli bacteria using swimming and tethering assays. We observed that the bacteria slowed down dramatically when subjected to Ag+ ions, providing direct evidence showing that Ag inhibits the motility of bacteria. In addition, through tethering assays, we monitored the rotation of flagellar motors and observed that the tumbling frequency of bacteria increased significantly in the presence of Ag+ ions. Furthermore, the rotation of bacteria in the tethering assays were analyzed using hidden Markov model (HMM); and we found that Ag+-treatment led to a significant decrease in the tumbling-to-running transition rate of the bacteria, suggesting that the rotation of bacterial flagellar motors was stalled by Ag+ ions. This work provided a new quantitative understanding on the mechanism of Ag-based antimicrobial agents in bacterial motility.

biophysics↗

bioRxiv2019

Faster diffusive dynamics of histone-like nucleoid structuring proteins in live bacteria caused by silver ions

The antimicrobial activity and mechanism of silver ions (Ag+) have gained broad attention in recent years. However, dynamic studies are rare in this field. Here, we report our measurement of the effects of Ag+ ions on the dynamics of histone-like nucleoid structuring (H-NS) proteins in live bacteria using single-particle tracking photoactivated localization microscopy (sptPALM). It was found that treating the bacteria with Ag+ ions led to faster diffusive dynamics of H-NS proteins. Several techniques were used to understand the mechanism of the observed faster dynamics. Electrophoretic mobility shift assay on purified H-NS proteins indicated that Ag+ ions weaken the binding between H-NS proteins and DNA. Isothermal titration calorimetry confirmed that DNA and Ag+ ions interact directly. Our recently developed sensing method based on bent DNA suggested that Ag+ ions caused dehybridization of double-stranded DNA (i.e., dissociation into single strands). These evidences led us to a plausible mechanism for the observed faster dynamics of H-NS proteins in live bacteria when subjected to Ag+ ions: Ag+-induced DNA dehybridization weakens the binding between H-NS proteins and DNA. This work highlighted the importance of dynamic study of single proteins in the live cells for understanding the functions of antimicrobial agents to the bacteria.

biophysics↗