Determination of the invertible element orientation in strain NU149 grown under different environmental conditions by PCR analysis. The PCR analysis was performed with chromosomal DNA isolated from NU149 cells grown in pH 7.0 LB medium with no added NaCl (low osmolarity), in pH 5.5 LB medium with no added NaCl (low osmolarity), and in pH 5.5 LB medium with 400 mM NaCl (high osmolarity), using the INV and FIMA primers to amplify phase-on-oriented DNA (450-bp product) and the FIME and INV primers to amplify phase-off-oriented DNA (750-bp product). The following dilutions were used for the PCR: undiluted (lanes 1), 1/2 (lanes2), 1/4 (lanes 3), 1/8 (lanes 4), 1/16 (lanes 5), 1/32 (lanes 6), 1/64 (lanes 7), 1/128 (lanes 8), and 1/256 (lanes 9). All PCR products were electrophoresed on 1.5% agarose gels.