Inactivation of Oriented Bacteria with Polarized Ultraviolet Light

Aligned deoxyribonucleic acid (DNA) molecules exhibit a large absorption anisotropy in the ultraviolet (UV) region of the spectrum (11). Also, the UV action spectra of most bacteria resemble the absorption spectrum of DNA (23), implying that inactivation is directly proportional to the UV absorbed by the bacterial DNA. Hence, the UV sensitivity of aligned uniaxial bacteria might be anisotropic with respect to polarization of the incident UV (17, 19). Any inactivation anisotropy would depend upon the orientation of DNA within the bacteria, as well as upon the alignment of bacteria, and could provide a more sensitive indication of in vivo DNA orientation than is presently available using optical methods (5, 12–16). Using an electric field of 3.5×106 cycles/second, samples of bacteria of strain LS-301 were aligned in a quartz cell and were irradiated with UV (λ = 2652 A) polarized perpendicular and parallel to the alignment direction. The resultant survival curves resolved no inactivation anisotropy. This result is interpreted to mean that there was insufficient bacterial DNA alignment to give a detectable anisotropy. The minimum average DNA alignment necessary to have resolved an anisotropy is calculated to be 15 per cent in an axial direction (bases perpendicular to the bacterial axis) or 30 per cent in a radial direction (bases parallel to the bacterial axis)