Significance of small molecules in control of quiescence and resuscitation in Synechocystis sp. PCC 6803

Abstract

Die Dissertation ist gesperrt bis zum 31. Dezember 2025 !

Bacterial dormancy is one of the most widespread survival mechanisms, ranging from short, like nocturnal sleep, to long term, like spores. Concomitant to a tightly regulated entry into dormancy, a just as regulated resuscitation process, like germination, is necessary. Dormancy is a ubiquitous response also present in the ubiquitous phylum of cyanobacteria. One member thereof, Synechocystis sp. PCC 6803, is unable to fix nitrogen and responds to deprivation of combined nitrogen sources with metabolic quiescence. This well-structured process leads to a degradation of phycobilisomes and thylakoid membranes, accumulation of glycogen, protein synthesis in preparation for recovery and reduction of energy, enabling cells to survive prolonged periods of starvation. To resuscitate in presence of combined nitrogen, glycogen is degraded to fuel re-establishment of the cell metabolism. In this work, we studied the significance of sodium and c-di-AMP in regulation of entry into and exit out of metabolic dormancy. Vegetative cells produce their energy through a photosynthesis-based, electrochemical H+ gradient at the thylakoid membranes. Dormant cells only keep reduced amounts of thylakoid membranes, reducing the capability of energy production. In this study, we describe the electrochemical Na+ gradient established on the cytoplasmic membrane, which secures energy synthesis. During resuscitation, sodium is then required for pH control and mitigation of osmotic stress. The second messenger c-di-AMP has been previously reported to influence night-time survival and osmotic stress response in cyanobacteria. This study revealed the influence of c-di-AMP on glycogen synthesis to be the pivotal factor in night-time survival. Furthermore, c-di-AMP is also essential for nitrogen starvation induced dormancy. The observed effects are global, once more influencing the accumulation of glycogen, though through a different mechanism than in diurnal rhythm. the underlying mechanisms and requirements for c-di-AMP in dormancy are subject of ongoing research.