Biology subjects

Tirumkudulu, M. S.

Publications and source records attributed to Tirumkudulu, M. S..

3 recordsLinked to original sources

bioRxiv2025

Effect of carrier droplet size and shape at different viral loads on virus stability during environmental drying

In the aftermath of the COVID-19 pandemic, airborne transmission has been identified as a significant factor in disease spread. However, there have been very few direct comparisons of virus viability in airborne droplets versus those deposited on surfaces or fomites. This study compares the viability of the enveloped Phi6 virus and two non-enveloped viruses (T4 and MS2) in droplets on hydrophobic and hydrophilic surfaces at 25{degrees}C and 45%-55% relative humidity. The former results in spherical droplets similar to airborne droplets, while the latter pertains to spreading droplets comparable to a fomite state. Our research highlights the influence of various physical factors of the carrier droplet--such as its shape and size--as well as the type and concentration of the virus on its viability during the drying process. We found that, at a fixed volume, virus viability decreased with droplet size in spherical droplets, while high initial viral concentrations ([~] 105 pfu/{micro}L) improved survival on fomites. This suggests that fomites from individuals with high viral loads pose a greater risk of infection. Overall, droplets of a specific volume are more viable in the air than on surfaces. Smaller airborne droplets may have decreased viability but can linger longer and penetrate deeper into the respiratory tract. When viral loads are high, its comparable persistence in both spherical and flat droplets increases the risk of fomite transmission. IMPORTANCEUnderstanding the roles of airborne and fomite transmission in respiratory diseases is essential for planning effective containment measures and resource allocation. Among the various factors that influence the spread of infection, the survival of viruses in drying droplets plays a critical role in disease transmission. In our study, we compare the viability of viruses in spherical droplets, which represent airborne transmission, and flat droplets, which represent fomite transmission. Our results indicate that virus viability is consistently higher in spherical droplets than in flat droplets when dried under similar conditions. However, for high virus loads, the difference in virus survival is significantly lower. Therefore, during an outbreak, it is important to monitor both the number of new infections and the viral load of infected individuals, as those with higher viral loads are more likely to spread the infection through both modes of transmission.

microbiology↗

bioRxiv2021

Effect of ligand sensing on flagellar bundle formation in bacteria

E. coli swims in liquid media by rotating long appendages called flagella. The direction of rotation of each flagellum is governed by a transmembrane rotary nanomotor, which receives signals from ligand-specific receptors. Attractants bias the motor to rotate in CCW direction causing flagella to bundle and provide thrust for locomotion. Recent studies have shown that sensing not only leads to increase in CCW bias but also increases the motor rotation speed due to the recruitment of additional stator units bound to the rotor. Despite the detailed studies on bacterial motility, the effect of ligand sensing on the synchronization of flagellar filaments leading to bundle formation and changes in bundle geometry are not clear. In this work, we performed real-time imaging of the flagellar bundle of swimming cells in metabolising (glucose) and non-metabolisable (2-Deoxy-d-glucose) attractants. We characterized bundles during swimming by measuring visible distal length and the spread of filaments at poles. We show that sensing of attractant by receptor leads to the formation of tight bundles when compared to control buffer. Contrary to previous studies, the swimming speeds were proportional to the bundle tightness with the latter dependent not only on the bias but also on the torque exerted by the motor. We further show that the observed wiggles in the swimming trajectory of cells is directly proportional to the spread angles of bundle and is effected by both motor CCW bias and torque. Mutant cells, which were rendered non-motile due to the absence of the PTS (phosphotransferase system) sugar uptake mechanism, exhibited motility when exposed to the non-metabolisable attractant confirming that mere sensing can induce torque in flagellar motor. These results clarify the role of sensing and metabolism on bundle formation and its impact on the motility of cells. Statement of significancePeritrichously flagellated E. coli swims away or towards ligands by biasing the direction of rotation of its flagellar motor. Recently, it has been shown that motor speed is also modulated on merely sensing a ligand. How does this impact flagellar bundle formation and swimming behavior? Using real-time imaging, we show that the bundle geometry changes in response to both metabolisable and non-metabolisable ligand. Mere sensing of a ligand temporarily increases the motor torque and CCW bias that causes tight flagellar bundles and leads to smooth swimming trajectories at high speeds. Our result provides strong evidence of a new signalling pathway that controls the flagellar motor speed to enable the bacteria to respond efficiently to changes in its environment.

biophysics↗

bioRxiv2020

Ligand Sensing Enhances Bacterial Flagellar Motor Output via Stator Recruitment

The phenomenon of chemotaxis in bacteria, where the cells migrate towards or away from chemicals, has been extensively studied in the past. For flagellated bacteria such as Escherichia coli, a change in chemical concentration in its environment is sensed by a chemoreceptor and communicated via a well-characterised signalling pathway to the flagellar motor. It has been widely accepted that the signals change the rotation bias of the motor without influencing the motor speed. Here, we present results to the contrary and show that the bacteria is also capable of modulating motor speed on merely sensing a ligand. Step changes in concentration of non-metabolisable ligand cause temporary recruitment of stators leading to a momentary increase in motor speeds. For metabolisable ligand, the combined effect of sensing and metabolism leads to higher motor speeds for longer durations. Swimming speeds measured at the population level corroborate the observations. Experiments performed with mutant strains delineate the role of metabolism and sensing in the modulation of motor speed and show how speed changes along with changes in bias can significantly enhance bacterias response to changes in its environment.

biophysics↗