The doubly phosphorylated form of HPr, HPr(Ser~P)(His-P), is abundant in exponentially growing cells of Streptococcus thermophilus and phosphorylates the lactose transporter LacS as efficiently as HPr(His~P).

In Streptococcus thermophilus, lactose is taken up by LacS, a transporter that comprises a membrane translocator domain and a hydrophilic regulatory domain homologous to the IIA proteins and protein domains of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). The IIA domain of LacS (IIALacS) possesses a histidine residue that can be phosphorylated by HPr(His~P), a protein component of the PTS. However, determination of the cellular levels of the different forms of HPr, namely, HPr, HPr(His~P), HPr(Ser-P), and HPr(Ser-P)(His~P), in exponentially lactose-growing cells revealed that the doubly phosphorylated form of HPr represented 75% and 25% of the total HPr in S.

Characterization of the cro-ori region of the Streptococcus thermophilus virulent bacteriophage DT1.

The virulent cos-type Streptococcus thermophilus phage DT1 was previously isolated from a mozzarella whey sample, and its complete genomic sequence is available. The putative ori of phage DT1 is characterized by three inverted and two direct repeats located in a noncoding region between orf36 and orf37. As the replication ability of the putative ori and flanking genes could not be established, its ability to confer phage resistance was tested.

Phosphorylation of Streptococcus salivarius lactose permease (LacS) by HPr(His ~ P) and HPr(Ser-P)(His ~ P) and effects on growth.

The oral bacterium Streptococcus salivarius takes up lactose via a transporter called LacS that shares 95% identity with the LacS from Streptococcus thermophilus, a phylogenetically closely related organism. S. thermophilus releases galactose into the medium during growth on lactose.

Genetic and biochemical characterization of the phosphoenolpyruvate:glucose/mannose phosphotransferase system of Streptococcus thermophilus.

In most streptococci, glucose is transported by the phosphoenolpyruvate (PEP):glucose/mannose phosphotransferase system (PTS) via HPr and IIAB(Man), two proteins involved in regulatory mechanisms. While most strains of Streptococcus thermophilus do not or poorly metabolize glucose, compelling evidence suggests that S. thermophilus possesses the genes that encode the glucose/mannose general and specific PTS proteins.