Abstract
Streptococcus thermophilus (S. thermophilus) and Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) are the economically important bacteria and are known for its worldwide application in yogurt production. The protocooperation between these two bacteria results in several benefits; an accelerated acidification, and stimulation of aromatic compounds and exopolysaccharides production etc. The genome analysis revealed that there are many pseudogenes in amino acid biosynthesis pathway and TCA pathway, suggesting an extensive and ongoing reductive evolution in both lactic acid bacteria as a coculture system to adapt growing in the milk environment rich with proteins and lactate. Both bacteria prefer the milk sugar lactose to glucose and they mutually supply essential components not only nutrition (peptides, amino acids, and formate etc.), but also components in metabolic pathways. The postgenomic analysis showed that the coculture resulted in much metabolic changes and regulatory relationship between the two bacteria.Our results using a knockout mutant of NADH oxidase of S. thermophilus revealed that oxygen consumption ability of the NADH oxidase is a new important factor of the protocooperation between two bacteria in yogurt production.
