Type I antibiotics:
Type I antibiotics would be the first to be induced in a situation of energetic stress, probably via “quorum sensing” (external) or c-di-GMP (internal) signals. These type I antibiotics, that include CDA and RED, are thought to create damage to the membrane, causing the lysis of a fraction of the population and the release of the cellular content of the lysed cells into the environment. The latter would be used as nutrient, and in particular as P source, for the surviving population. This supply of P would support the activation of the oxidative metabolism of the strain in order to restore its energy balance. This phenomenon of programmed cell death (PCD: Programmed Cell Death) is well documented in Streptomyces. The possible role of CDA in PCD has already been discussed and that of RED has been recently demonstrated. PCD of a fraction of the basal mycelium would allow the growth of aerial hyphae which, under adverse conditions, are organs of spores dissemination.
However, when phosphate originating from cell lysis is depleted, the activation of oxidative metabolism and oxidative phosphorylation (ATP synthesis) cannot be sustained. It is in this context that Type II antibiotics are being produced.