Journal
MICROBIOLOGY-SGM
Volume 155, Issue -, Pages 1953-1965Publisher
MICROBIOLOGY SOC
DOI: 10.1099/mic.0.024737-0
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Funding
- Italian National Research Council [AG.P04.015, RSTL 862]
- Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR)
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Streptococcus thermophilus is a major component of dairy starter cultures used for the manufacture of yoghurt and cheese. In this study, the CO2 metabolism of S. thermophilus DSM 20617(T), grown in either a N-2 atmosphere or an enriched CO2 atmosphere, was analysed using both genetic and proteomic approaches. Growth experiments performed in a chemically defined medium revealed that CO2 depletion resulted in bacterial arginine, aspartate and uracil auxotrophy. Moreover, CO2 depletion governed a significant change in cell morphology, and a high reduction in biomass production. A comparative proteomic analysis revealed that cells of S. thermophilus showed a different degree of energy status depending on the CO2 availability. In agreement with proteomic data, cells grown under N-2 showed a significantly higher milk acidification rate compared with those grown in an enriched CO2 atmosphere. Experiments carried out on S. thermophilus wild-type and its derivative mutant, which was inactivated in the phosphoenolpyruvate carboxylase and carbamoyl-phosphate synthase activities responsible for fixing CO2 to organic molecules, suggested that the anaplerotic reactions governed by these enzymes have a central role in bacterial metabolism. Our results reveal the capnophilic nature of this micro-organism, underlining the essential role Of CO2 in S. thermophilus physiology, and suggesting potential applications in dairy fermentation processes.
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