Influence of arginine on the growth, arginine metabolism and amino acid consumption profiles of Streptococcus thermophilus T1C2 in controlled pH batch fermentations

AimsThe aim of this study was to elucidate the effect of arginine on the growth, arginine metabolism and amino acid consumption profiles of Streptococcus thermophilus T1C2. Methods and ResultsThe growth kinetics, intracellular pH, extracellular osmotic pressure, expression of key genes in the arginine metabolism pathway and amino acid consumption profiles were analysed in chemically defined medium with different initial arginine concentrations. The results showed that arginine stimulated the growth of Strep.thermophilus T1C2 under low intracellular pH and high extracellular osmotic pressure. The expression of key genes in the arginine degradation pathway indicated that arginine relieved the drop in the intracellular pH by consuming protons and generating NH3. Additionally, the results showed that arginine degradation did not occur via the arginine deiminase pathway but through the arginine decarboxylase-urease pathway. Furthermore, the utilization efficiency of amino acids was improved in the presence of arginine. ConclusionsArginine improved the growth of Strep.thermophilus due to protecting Strep.thermophilus against intracellular acid stress, which was revealed at the transcriptional level of key genes. This study showed that the acid resistance of Strep.thermophilus was achieved through the arginine decarboxylase-urease pathway. Significance and Impact of the StudyThe arginine-stimulated growth of Strep.thermophilus improved the utilization efficiency of amino acids and reduced nitrogen waste, which could be useful for the optimization of cultivation media.