Fluid Dynamics of Multiple Fast-Firing Extrusomes : Fast extrusomes

Area of Science:

• Biophysics
• Fluid Dynamics
• Cell Biology

Background:

• Microscale interactions in fluids are dominated by viscosity and boundary layers, making cell contact difficult.
• Ultra-fast extrusive organelles (extrusomes) in various organisms, such as jellyfish nematocysts, overcome these challenges by firing rapidly.
• Previous studies focused on single extrusome firing; the fluid dynamics of multiple extrusomes remain understudied.

Purpose of the Study:

• To numerically simulate the fluid dynamics of multiple simultaneously or sequentially fired barb-like structures (extrusomes).
• To investigate the impact of varying Reynolds numbers on extrusome-prey interactions.
• To understand the physical mechanisms governing the success of multiple extrusome firing.

Main Methods:

• Utilized the immersed boundary method for two-dimensional numerical simulations.
• Modeled the dynamics of one, two, and three accelerated barb-like structures released towards a passive elastic prey.
• Varied the Reynolds number across several orders of magnitude to cover biologically relevant firing speeds and fluid conditions.

Main Results:

• A nonmonotonic relationship exists between prey distance and Reynolds number for simultaneously fired barbs.
• At higher Reynolds numbers, boundary effects are less significant, allowing barbs to directly impact prey.
• At lower Reynolds numbers, fluid entrainment by barbs increases their range.
• Center barbs consistently hit prey at the highest Reynolds numbers, irrespective of firing order or spacing.

Conclusions:

• The fluid dynamics at the microscale are highly nonlinear, leading to complex interactions.
• Multiple extrusome firing strategies can be effective, with center barbs showing robustness.
• Understanding these fluid dynamics is crucial for comprehending extrusome function in biological systems.