Comparative Transcriptomic Analysis of Streptococcus thermophilus TH1436 and TH1477 Showing Different Capability in the Use of Galactose

Abstract

Streptococcus thermophilus is a species widely used in the dairy industry for its capability to rapidly ferment lactose and lower the pH. The capability to use galactose produced from lactose hydrolysis is strain dependent and most of commercial S. thermophilus strains are galactose-negative (Gal−), although galactose-positive (Gal+) would be more technologically advantageous because this feature could provide additional metabolic products and prevent galactose accumulation in foods. In this study, a next generation sequencing transcriptome approach was used to compare for the first time a Gal+ and a Gal− strain to characterize their whole metabolism and shed light on their different properties, metabolic performance and gene regulation. Transcriptome analysis revealed that all genes of the gal operon were expressed very differently in Gal+ and in the Gal− strains. The expression of several genes involved in mixed acid fermentation, PTS sugars transporter and stress response were found enhanced in Gal+. Conversely, genes related to amino acids, proteins metabolism and CRISPR associated proteins were under-expressed. In addition, the strains showed a diverse series of predicted genes controlled by the transcriptional factor catabolite control protein A (CcpA). Overall, transcriptomic analysis suggests that the Gal+ strain underwent a metabolic remodeling to cope with the changed environmental conditions.

Short communication: Lactose utilization of Streptococcus thermophilus and correlations with β-galactosidase and urease

“…The S. thermophilus strains were in the de Man, Rogosa, and Sharpe (MRS)-lactose broth with 2% lactose as the sole carbon source and were incubated at 37°C for 12 h under aerobic conditions before the analysis. After washing with a saline solution, the bacteria were transferred into the fresh MRS-lactose medium to an initial concentration of 5 × 10 6 cells/mL to record their growth, acid production, and rate of lactose utilization during incubation at 37°C for 16 h under aerobic conditions (Giaretta et al, 2018;Yang et al, 2019). After 12 h of incubation, the urease and β-galactosidase activities of the strains were determined as previously described, with 1 unit of urease activity defined as the release of 1 µmol of NH4 + per min (Mora et al, 2005;Zotta et al, 2008;Wu and Shah, 2017).…”

Comparative Genomics of Streptococcus thermophilus Support Important Traits Concerning the Evolution, Biology and Technological Properties of the Species

“…Recently, Xiong et al (2019b) demonstrated that the Gal + phenotype of S. thermophilus depends upon the expression of the gal operon, which can be widely affected by a single point mutation at the -9 box in the galK promoter. Since the accumulation of galactose in the medium by S. thermophilus may be important from a technological or nutritional perspective (Giaretta et al, 2018), we examined the presence of the mutation at the -9 box in the galK promoter in the strains analyzed. Accordingly, only B59671, CS8, EPS, and NCTC12958 T seem to be able to catabolize galactose, as they own the relevant G to A mutation in the position -9 of the -10 box related Gal + phenotype (data not shown).…”

Genomic and phenotypic analyses of exopolysaccharide biosynthesis in Streptococcus thermophilus S-3

“…This suggests that this single point mutation of the galK promoter may largely be responsible for the Gal + phenotype of S-3. Giaretta et al (2018) also compared the gal promoters of Gal + and Gal − strains and found mutations at various positions in the gal operon intergenic regions. These mutations result in insufficient expression of the gal operon genes in the Gal − strains.…”