Compartimenti funzionali nella cellula batterica. 2. Ripresa della crescita dopo rinfresco della coltura

Ageno, Mario

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 82 (1988) no. 1, pp. 145-150

Résumé

When some bacterial cells are removed from a saturated culture and transferred to a glucose-rich new medium, they resume growing if a set of conditions are satisfied. Glucose catabolism resumes almost immediately, as well as protein synthesis. However, cells do not divide during the first 30-60 minutes, after which the cell number starts growing suddenly. The lag can be due neither to insufficient energy supply to the cell, nor to a substance, synthesized constitutively, whose concentration does not reach a threshold. We show that there are two kinds of molecules in the cell: a) building materials, which are products of glucose catabolism and grow in number exponentially with the age of the cell; and b) control molecules, which are coded in the DNA and grow in number parabolically with the age of the cell. At the beginning, the effective lengths of the cells are smaller in the refreshing medium than in the mother culture during the exponential phase of growth. Now, the cells have an excess of DNA with regard to their length. They do not divide as far as the control molecules are sufficient in number to work out all the building materials. However, an exponential growth of the building materials eventually exceeds any parabolic growth of the control molecules, and the internal processes of the cell cannot remain coerent for ever. When the level of inexhausted materials reaches an enzymatic threshold, the division process starts. In this way, cell division reveals itself a process of recovering.