Profiles of Streptococcus thermophilus MN-ZLW-002 nutrient requirements in controlled pH batch fermentations

Abstract

This study aimed to evaluate the profiles of Streptococcus thermophilus nutrient requirements to guide the design of media for high cell density culturing. The growth kinetics, physiological state, and nutrient requirement profiles of S. thermophilus were analyzed in chemically defined media. The results showed that the intracellular ATP concentration, H⁺ -ATPase activity, NADH/NAD⁺ , and NH₃ concentrations varied with intracellular pH. The nutrient components with the highest amounts required were Leu and Asp; ascorbic acid and p-amino benzoic acid; K⁺ and PO₄^3- ; and guanine and uracil. The nutrient components with the largest required ratios were Arg, His, and Met; folic acid, cyanocobalamine, biotin, and nicotinic acid; Ca²⁺ and Mg²⁺ ; and guanine and uracil. In this study, different nutrient components were primarily used at different phase. Trp, Tyr, calcium pantothenate, thiamine, guanine, and Mg²⁺ were mainly used from late-lag to midexponential phase. Met, Pro, Phe, Ala, Gly, nicotinic acid, and riboflavin were mainly used from midexponential to late-exponential phase. The highest bioavailabilities of nutrient components were also found at diverse phase. Met, Leu, Ile, Asn, Glu, Lys, Pro, Gly, riboflavin, nicotinic acid, adenine, uracil, inosine, and Ca²⁺ had the highest bioavailability from late-lag to midexponential phase. Lactose, Glu, Asp, His, Trp, Cys, Val, Arg, Phe, Ala, Ser, Thr, Tyr, folate and cobalamin, calcium pantothenate, ascorbic acid, thiamine, biotin, p-amino benzoic acid, vitamin B₆ , K⁺ , Mg²⁺ , guanine, xanthine, and PO₄^3- had the highest bioavailability from midexponential to late-exponential phase. This study elucidated the nutrient requirement profiles with culture time and biomass at various average growth rates during the growth of S. thermophilus. The present results will help to formulate complex media for high cell density cultivation and provide the theoretical basis for S. thermophilus feeding strategies.

Keywords: S. thermophilus; amino acid; inosine; purine; pyrimidine; requirement profiles; vitamin.