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

- Folate production by S. thermophilus CRL803 is affected by external pH conditions.
- First study where fol genes expression is influenced by culture conditions.
- Viable/non-culturable cells can express fol genes and produce folates.

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 °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.This is the first study on the expression of fol mRNA and their relation with folate synthesis by S. thermophilus, which is influenced by culture conditions.