Abstract
Micro-engineering pumping devices without mechanical parts appeared “way back” in the early 1990’s. The working principle is acoustic streaming. Has Nature “rediscovered” this invention 2.7 Gyr ago? Strands of marine cyanobacteria Synechococcus swim 25 diameters per second without any visible means of propulsion. We show that nanoscale amplitude vibrations on the S-layer (a crystalline shell outside the outer membrane present in motile strands) and frequencies of the order of 0.5-1.5 MHz (achievable by molecular motors), could produce steady streaming slip velocities outside a (Stokes) boundary layer. Inside this boundary layer the flow pattern is rotational (hence biologically advantageous). In addition to this purported “swimming by singing”, we also indicate other possible instantiations of acoustic streaming. Sir James Lighthill has proposed that acoustic streaming occurs in the cochlear dynamics, and new findings on the outer hair cell membranes are suggestive. Other possibilities are membrane vibrations of yeast cells, enhancing its chemistry (beer and bread, keep it up, yeast!), squirming motion of red blood cells along capillaries, and fluid pumping by silicated diatoms.
Highlights
This essay is devoted to a little invention by Engineers, that we speculate cyanobacteria anticipated much earlier
We believe that acoustic streaming explains the motility of Synechococcus, and that many other examples in cell biology should exist
We show that the photosynthetic membranes of two distantly related cyanobacterial species contain multiple perforations
Summary
This essay is devoted to a little invention by Engineers, that we speculate cyanobacteria anticipated much earlier. Half way back in the history of life, marine cyanobacteria invented photosynthesis. We believe that acoustic streaming explains the motility of Synechococcus, and that many other examples in cell biology should exist. As we will discuss, there is a extra bonus: acoustic streaming produces a “chaotic fluid atmosphere” around the cell, that enhances mixing and nutrient uptake. This Arbor issue is a tribute to Darwin’s year-2009, his bicentennial and sesquicentennary of “The origin of species” (Darwin, 1859) [15].
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