New Methods for Determining Induction Rate of Prophage in Lysogenic Bacteria

Two new methods，colony counting method and plate inducing method，were established for determining ultraviolet induction rate of prophage in the present study．Culture of lysogenic bacteria (λ)which was induced hy ultraviolet irradiation and cultivated in dark was directly spread on the plate，and induction rate of prophage was calculated based on the CFUs(colony form ing units)．The plate with mixture of lysogenic bacteria and indicator strain was induced by ultraviolet irradiation．The induction rate of prophage was calculated based on the PFUs(plaque form ing units)．These two methods not only can determ ine precisely induction frequency of prophage。but also are easy tO ma— nipulate ，and they can save efforts and apparatus，they are also easy to repeat．Furthermore，the m ix— ture of Cordyceps sinensis extract and lysogenic bacteria was irradiated with U V ．The results demon— strate that the new methods are practical and easy tO conduct，and that Cordyceps sinensis has a strong protection effect against U V—irradiation．