Transcriptomic response of 6 Propionibacterium freudenreichii strains during cold storage

Propionibacterium freudenreichii is used as a ripening culture in Swiss cheese manufacture. It produces flavor compounds over the whole ripening period. During cheese ripening, P. freudenreichii is exposed to a temperature downshift, especially when cheeses are transferred from warm temperature (about 24°C) to cold temperature (about 4°C). The cold adaptation of the type strain was studied previously. The aim of this study was to investigate the adaptation of 6 other P. freudenreichii strains at cold temperature by means of a global gene expression profile. The temporal transcriptomic response of 6 P. freudenreichii strains was analyzed at 2 times of growth, during growth at 30°C then after 3 days 4°C, in the constant presence of lactate as the main carbon source. Six strains were used: CIRM-BIA9, CIRM-BIA118, CIRM-BIA122, CIRM-BIA123, CIRM-BIA472, CIRM-BIA482. Gene expression was measured in the middle of exponential growth phase at 30°C (20h, OD650 ≈ 0.5), and after 3days of incubation at 4°C. Three independent biological experiments were performed for each strain and at each time, and were labelled A, B, C. Five technical repetitions were performed using the RNA of 3J_122B, 3J_123A, 3J_472C, 20H_9A and 20H_482C samples. These technical repetitions were labelled 3J_122Bii, 3J_123Aii, 3J_472Cii, 20H_9Aii and 20H_482Cii respectively. The transcriptomic data for 20H_122A and 3J_123C samples were abberant and were thus not considered for further analysis.