Improvement of Detection and Production of Propionicin PLG-1, a Bacteriocin Produced by Propionibacterium thoenii ^†

Propionibacterium thoenii P127 produces propionicin PLG-1 in liquid culture at relatively low concentrations and slow production rates. The goal of this study was to increase the sensitivity and reproducibility of the standard well-diffusion assay for bacteriocin activity as well as to improve production of propionicin PLG-1 under controlled conditions in a fermenter. Several conditions were varied in the well-diffusion assay. The best results were obtained with 7-mm wells cut into a 5-mm-deep base layer that contained 2.5% agar, 0.85% NaCl and 0.1 % Tween 80. Plates were incubated at room temperature for 24 h or at 37°C for 2 h before adding bacteriocin samples to the wells to aid diffusion. Larger and clearer zones of inhibition were observed when Lactobacillus delbrueckii ATCC 4797 rather than Propionibacterium acidipropionici P5 was used as indicator strain, and results could be read in 12 h. Recovery of bacteriocin from the culture supernatant was improved by adding 0.1% Tween 80 to the buffer used for dialysis and resuspension of precipitated protein. Strain P127 was grown in six different media under controlled conditions in a fermenter: 12.5% beet molasses; 9% corn steep liquor; combinations of beet molasses and corn steep liquor at 1:3, 1:1, and 3:1 (vol:vol) ratios; and the standard growth medium, sodium lactate broth. Maximum production of propionicin PLG-1 was obtained in 3:1 beet molasses:corn steep liquor, and was 5 times greater than in sodium lactate broth.