A simple photometric method for determination of the activity of pyrocin R1

A simple photometric method for rapid and accurate determination of the activity of pyocin R1, a bacteriocin produced by Pseudomonas aeruginosa strain P15, has been developed. This method is based on the turbidity-decrease observed when the bacteriocin is added to a suspension of sensitive bacteria P. aeruginosa strain P11. Optimum conditions for the turbidity-decreasing activity of pyocin R1 are in 0.01 M Tris-HCl buffer containing 0.2 M NaCl (pH 7.5) at 37 degrees C. A good correlation was found between the dose of pyocin R1 and the rate of the turbidity-decrease (with a correlation coefficient of more than 0.98). The amount of pyocin R1 required for this assay is nearly the same as that used for the conventional colony-counts method. The assay for one sample takes less than 3 min, whereas an overnight wait is necessary for the conventional method. This method is shown to be very suitable for following the time course of activity change observed when pyocin R1 is treated with various chemicals, including receptor substances obtained from sensitive cells. The turbidity-decrease assay was also found to be applicable to the determination of activities of other R-type pyocins.