DNA degradation by acoustic microstreaming

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Abstract
Calf thymus DNA in saline buffer (SSC) was irreversibly degraded by the acoustic microstreaming field generated around submerged portions of a transversely oscillating steel wire. Free radical scavenging agents (e.g., I131) were firmly (covalently?) bound to sheared fragments, strongly indicating covalent bond rupture during cleavage of the DNA backbone. All molecular weight estimations were made by viscometry under “zero-shear” conditions and showed that DNA of initial average molecular weight 9.34 × 106 daltons was not degraded until the wire displacement amplitude exceeded 18 μm. At any given amplitude above this threshold, the measured molecular weight decreased asymptotically with time of exposure and was usually within 5% of its limiting value after 5 min. Each original average molecule was halved after 5 min shear at 28 μm and quartered at a displacement amplitude of 59 μm. Approximate lower limits were estimated for the velocity gradients existing near the wedge-shaped wire trip; this gave a critical shear rate of about 105 sec−1 to cleave each original DNA molecule, and an average breeding force of about 5 × 10−5 dyn.

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