Detection and partial purification of Salmonella serovar Typhimurium cytotoxic protein affecting seed germination

Cells of a virulent strain of Salmonella Typhimurium (E-2391), a highly ubiquitous and zoonotic serovar, were sonicated and the cell-free supernatant was precipitated using increasing concentration of ammonium sulphate (30–80%). Inhibition of seed germination by various precipitated fractions revealed that the activity was present in the fraction precipitated at 70% saturation of ammonium sulphate. Out of the two peaks obtained on Seralose 6B chromatography, the second peak was found to possess germination-inhibition activity at a level as low as 0.1 mg/ml of this protein. SDS-PAGE revealed the presence of fewer proteins in the second peak but no specific protein responsible for the inhibition could be deduced. The study indicated that the in vitro seed germination inhibition technique can be utilized for testing of Salmonella isolates for the cytotoxic properties instead of resorting to expensive in vivo methods involving use of animals.