Folate production and fol genes expression by the dairy starter culture Streptococcus thermophilus CRL803 in free and controlled pH batch fermentations

摘要

Folate production by Streptococcus thermophilus CRL 803 was examined during batch fermentations without pH control and at constant pH (6.0 and 5.0) at different incubation temperatures. Folate production was higher at 42 degrees C under both constant and non-constant pH fermentation conditions, the increase being more pronounced at constant pH 6.0. Folate production by S. thermophilus CRL 803 under different fermentation conditions was cell-growth-associated. These observations were supported by analysis at the transcriptional levels of fol genes in controlled pH of 6.0 and uncontrolled pH batch culture. At pH 6.0, the highest relative expression levels of folE, folQ folk and folP genes (involved in de novo synthesis) were observed after 6 h of incubation.