Effects of heat shock on gram negative bacteria: use of lysis by sodium dodecyl sulphate as a probe for the integrity of DNA.

Rheograms of Alcaligenes eutrophus (NCIMB 40529) and Escherichia coli (C90 NCIMB 10616) cells lysed by sodium dodecyl sulphate were compared before and after a variety of heat shock regimes. It was found that unheated cells produced a very characteristic shear thickening rheogram which could be destroyed by DNase treatment. Cells which had been subjected to heat shock produced rheograms very similar to DNase digested material. We thus suggest that the rheogram is largely due to the presence of intact DNA molecules. The extent and nature of the heat shock affected the shape of the rheogram of the SDS lysed material. Heat shock of cells after SDS lysis did not appear to significantly damage the DNA. Storage of the cells at 10 degrees C before heat shock considerably reduced the shear thinning effect of subsequent heat shock at 90 degrees C. We attribute the shear thinning effect of the heat shock to the action of nucleases which are activated and then depolymerise the DNA molecules.