Could cell membranes produce acoustic streaming? Making the case for Synechococcus self-propulsion

Abstract

Sir James Lighthill proposed in 1992 that acoustic streaming occurs in the inner ear, as part of the cochlear amplifier mechanism. Here we hypothesize that some of the most ancient organisms use acoustic streaming not only for self-propulsion but also to enhance their nutrient uptake. We focus on a motile strain of Synechococcus, a cyanobacteria whose mechanism for self-propulsion is not known. Molecular motors could work like piezoelectric transducers acting on the crystalline structure surrounding the outer cell membrane. Our calculations show that a traveling surface acoustic wave (SAW) could account for the observed velocities. These SAW waves will also produce a non-negligible Stokes layer surrounding the cell: motion within this region being essentially chaotic. Therefore, an AS mechanism would be biologically advantageous, enhancing localized diffusion processes and consequently, chemical reactions. We believe that acoustic streaming, produced by nanometer scale membrane vibrations could be widespread in cell biology. Other possible instances are yeast cells and erythrocytes. Flows generated by acoustic streaming may also be produced by silica coated diatoms along their raphe. We note that microelectromechanical (MEMS) acoustic streaming devices were first introduced in the 1990's. Nature may have preceded this invention by 2.7 Gyr.

The Putative Eukaryote-LikeO-GlcNAc Transferase of the Cyanobacterium Synechococcus elongatus PCC 7942 Hydrolyzes UDP-GlcNAc and Is Involved in Multiple Cellular Processes

“…Marine strains of S. elongatus have motility despite having no known locomotion organelles such as cilia or flagella (24,25). Several membrane-related mechanisms for S. elongatus motility have been proposed, including localized expansion and contraction of the cell membrane (26), acoustic streaming (27), mechanochemical filaments near the inner membrane causing surface waves (28), and a helical rotor model (29). In a Synechococcus species related to S. elongatus PCC 7942 several genes involved in motility (30), including ABC transporters, glycosyltransferases, and the cell surface polypeptide SwmA, which forms a glycosylated S layer (31), have been identified.…”

Acoustic Streaming, The “Small Invention” of Cianobacteria?

“…We have set our bibliography to the magic number 100, combining technical and non-technical articles. Technical details of our model are presented in (Ehlers and Koiller, 2010) [20]). Our calculations show that cell membrane vibrations with nano-scale amplitudes and frequencies below 1 MH can produce bulk fluid motion of the order of tens of microns per second.…”

“…He could not complete his theory outlined in (Lighthill, 1992) [43]). The cochlear amplifier mechanism is a theme of intense debate among the experts (see http:// www.mechanicsofhearing.org/ for their regular meetings), but nonetheless we took the nerve to make a small speculation in [20], about a fluid mediated amplification, involving a positive feedback between the inner and outer hair cells.…”

“…A thriving company is Advalytix (http://www.advalytix.com/), founded in 2000 as an spin-off of a consortium of German universities 19 . One of the co-founders is Axim Wixforth, from the Physics Department at Augsburg 20 . For work being done in other labs, see the program of the recent meeting http://2009prato.net/Home.html.…”

“…This is because in the AS equations, some portion of the inertial term of the Navier-Stokes equations is retained, even in the low Reynolds regime. For details, see (Ehlers and Koiller, 2010) [20]). …”