Centrifugal field effects on the sedimentation coefficient of the Escherichia coli nucleoid after heat treatment.

The effects of the centrifugal field on the sedimentation coefficient of the heated (50 degrees C, 30 min) Escherichia coli nucleoid were investigated. Form 3,000 r.p.m. the sedimentation coefficients of the heated nucleoids were highly dependent on rotor speed. At 3,000 r.p.m. thier sedimentation coefficient was about 4,000 S while at 7,000 r.p.m. if was about 1,500-1,700 S. At 7,000 r.p.m. and over, nucleoid aggregations occurred and it was difficult to differentiate speed dependence from nucleoid aggregation. Factors likely to cause speed dependence and/or nucleoid aggregation are indicated. The practical importance of these findings is pointed out.