  Certain cyanobacteria, such as open ocean strains of Synechococcus, are able
to swim at speeds up to 25 diameters per second, without flagella or visible
changes in shape. The means by which Synechococcus generates thrust for
self-propulsion is unknown. The only mechanism that has not been ruled out
employs tangential waves of surface deformations. In Ehlers et al, the average
swimming velocity for this mechanism was estimated using the methods
inaugurated by Taylor and Lighthill in the 1950's and revisited in differential
geometric language by Shapere and Wilczek in 1989. In this article we propose
an entirely different physical principle self propulsion based on acoustic
streaming (AS). Micro-pumps in silicon chips, based on AS, have been
constructed by engineers since the 1990's, but to the best of our knowledge
acoustic streaming as a means of microorganisms locomotion has not been
proposed before. Our hypothesis is supported by two recent discoveries: (1) In
Samuel, et al, deep-freeze electron microscopy of the motile strain WH8113
revealed a crystalline outer layer (CS) covered with a forest of "spicules"
(Sp) extending from the inner membrane through the CS, projecting 150 nm into
the surrounding fluid. (2) In Pelling et al, atomic force microscopy (AFM) was
used to find that the cell wall of yeast cells periodically oscillates on
nano-scale amplitudes at frequencies of 0.8 to 1.6 kHz, and that the
oscillations are generated metabolically. We propose that the spicules, in
contact with the cell's power systems, could perform high frequency motions
generating acoustic streaming (AS) in the surrounding fluid. We compare two
models for self-propulsion employing acoustic streaming: the quartz wind effect
(QW) and boundary induced streaming generated by surface acoustic waves (SAW).
