Recovery of Unicellular Cyanobacteria from Nitrogen Chlorosis: A Model for Resuscitation of Dormant Bacteria

Abstract

Nitrogen starvation induces developmental transitions in cyanobacteria. Whereas complex multicellular cyanobacteria of the order Nostocales can differentiate specialized cells that perform nitrogen fixation in the presence of oxygenic photosynthesis, non-diazotrophic unicellular strains, such as <i>Synechococcus elongatus</i> or <i>Synechocystis</i> PCC 6803, undergo a transition into a dormant non-growing state. Due to loss of pigments during this acclimation, the process is termed chlorosis. Cells maintain viability in this state for prolonged periods of time, until they encounter a useable nitrogen source, which triggers a highly coordinated awakening process, termed resuscitation. The minimal set of cellular activity that maintains the viability of cells during chlorosis and ensures efficient resuscitation represents the organism’s equivalent of the BIOS, the basic input/output system of a computer, that helps “booting” the operation system after switching on. This review summarizes the recent research in the resuscitation of cyanobacteria, representing a powerful model for the awakening of dormant bacteria.

Genome Analysis Coupled With Transcriptomics Reveals the Reduced Fitness of a Hot Spring Cyanobacterium Mastigocladus laminosus UU774 Under Exogenous Nitrogen Supplement

“…It is unclear whether these genes are acquired after UU774 diverged from PCC 9339 some 198 million years ago (Figure 1). While non-diazotrophic cyanobacteria undergo severe stress during nitrogen starvation that leads to chlorosis and proteolytic degradation that leads to dormancy (Neumann et al, 2021), with complex multi-cellular forms such as UU774 develop heterocysts. The cassettes of genes in scaffold_38 with the upregulation in the nitrogen depleted condition during starvation are possibly an indication that it is imparting adaptive advantages and is possibly indispensable.…”

Phosphorylation of phosphoglucomutase 1 on a peripheral site tunes its activity to regulate glycogen metabolism

“…PCC 6803 (from now Synechocystis ). 5,6 When Synechocystis encounters nitrogen depletion, the intracellular carbon/nitrogen balance is disturbed, and growth can no longer be supported. This metabolic situation leads to rapid accumulation of glycogen, which serves as a sink for the excess of carbon.…”

“…As a result of the metabolic and morphological changes induced by nitrogen starvation, cells enter a dormant state, which allows them to survive adverse conditions for a prolonged period of time. 6 Upon nitrogen availability, the glycogen stores accumulated in dormant cells play a key role in the restoration of vegetative growth. 7 When dormant cells have access to a nitrogen source, their metabolism switches towards a glycolytic phase.…”

Quiescence Through the Prism of Evolution

“…For example, S. cerevisiae responds immediately to an extracellular food supply (Zhang et al, 2019) and many of the cellular machineries reorganized upon quiescence establishment, such as the actin cytoskeleton or the proteasome, are mobilized within seconds upon carbon replenishment (Sagot et al, 2006;Laporte et al, 2008Laporte et al, , 2011. Furthermore, during the first step of resuscitation from chlorosis of nitrogen starved cyanobacteria, an almost instantaneous increase in the adenosine triphosphate (ATP) level is observed upon addition of sodium nitrate (Neumann et al, 2021), just as in quiescent S. cerevisiae upon glucose re-feeding (Laporte et al, 2011). Besides, in S. cerevisiae, the polymerase II is poised onto promoter of genes that are critical for proliferation resumption (Radonjic et al, 2005).…”