Metabolic capabilities of Lactococcus lactis: Flavor, amino acids and phenotypic heterogeneity

The research performed in this thesis focuses on various aspects of the metabolism of the bacterium Lactococcus lactis. The role that L. lactis plays in the food industry is related to flavor formation. In this thesis, biosensors to detect flavor-promoting compounds were developed. However, that initial aim took Jhonatan Hernandez-Valdes to other research questions that he wanted to answer. Therefore, this thesis consists of two sections. The first part comprehends the development of biosensors for the detection of flavor-promoting compounds. The second part is the result of his curiosity-driven research, where he shows his interest on bacteria as single cells that perform essential processes, as single-species populations, and as members of a mixed-cell population that have to interact with other species. This thesis includes a remarkable discovery of the heterogeneous methionine uptake. This bacterium is unable to produce methionine and thus, it must import it from the environment. Surprisingly, some cells use one transporter and other cells use another transporter. The cells stick to their choice for more tan ten generations. It is the first time that scientists observe such a stable heterogeneity. The work on the methionine requirement of L. lactis was rewarded by this important discovery. This is not only an example of serendipity, but also of how complex the genetic regulation has evolved in L. lactis. The author believes his thesis will aid the development of technologies to broaden our L. lactis knowledge, and yields new tools to enhance its applications