Changes in protein synthesis during thermal adaptation of Propionibacterium freudenreichii subsp shermanii

Dairy propionibacteria are present in Graviera Kritis, a traditional Gruyere-type cheese made without added propionic starter. Ten isolated strains were identified by a combination of SDS-PAGE, species-specific PCR and according to their ability to fennent lactose. They were all found to belong to the Propionibacteriumfretidenreichii subsp. shermanii species. Because of the stressing Gruyere technology, which includes cooking at 52 to 53 degrees C their thermotolerance was investigated at 55 degrees C. Thermotolerant and thennosensitive strains were clearly discriminated. Interestingly, the reference strain CIP 103027 belongs to the sensitive subset. One sensitive strain, ACA-DC 1305 and one tolerant, ACA-DC 1451, were selected for further study and compared to CIP 103027. For the sensitive strains ACA-DC 1305 and CIP 103027, heat pre-trcatment at 42 degrees C conferred thennoprotection of cells at the lethal temperature of 55 degrees C, while there was less effect on the tolerant ACA-DC 1451. No crossprotection of salt-adapted cells against heat stress was observed for none of the strains. Differential protcomic analysis revealed distinct but overlapping cell responses to heat stress between sensitive and tolerant strains. Thermal adaptation upregulated typical HSPs involved in protein repair or turnover in the sensitive one. In the tolerant one, a distinct subset of proteins was overexpressed, whatever the temperature used, in addition to HSPs. This included enzymes involved in propionic fermentation, amino acid metabolism, oxidative stress remediation and nucleotide phosphorylation. These results bring new insights into then-noprotection in propionibacteria and the occurrence of divergent phenotypes within a same subspecies. (c) 2006 Elsevier B.V All rights reserved.