Nitrogen-starvation-induced chlorosis in Synechococcus PCC 7942: adaptation to long-term survival

Abstract

When deprived of essential nutrients, the non-diazotrophic cyanobacterium Synechococcus sp. strain PCC 7942 undergoes a proteolytic degradation of the phycobiliproteins, its major light-harvesting pigments. This process is known as chlorosis. This paper presents evidence that the degradation of phycobiliproteins is part of an acclimation process in which growing cells differentiate into non-pigmented cells able to endure long periods of starvation. The time course of degradation processes differs for various photosynthetic pigments, for photosystem I and photosystem II activities and is strongly influenced by the illumination and by the experimental conditions of nutrient deprivation. Under standard experimental conditions of combined nitrogen deprivation, three phases of the differentiation process can be defined. The first phase corresponds to the well-known phycobiliprotein degradation, in phase 2 the cells lose chlorophyll a prior to entering phase 3, the fully differentiated state, in which the cells are still able to regenerate pigmentation after the addition of nitrate to the culture. An analysis of the protein synthesis patterns by two-dimensional gel electrophoresis during nitrogen starvation indicates extensive differential gene expression, suggesting the operation of tight regulatory mechanisms.

Signal Transduction Protein P II Is Required for NtcA-Regulated Gene Expression during Nitrogen Deprivation in the Cyanobacterium Synechococcus elongatus Strain PCC 7942

“…When ammonium was used as a nitrogen source, the nitrate salt from BG11 was replaced by 5 mM NH 4 Cl and the medium was buffered to pH 8.0 with 5 mM HEPES. Illumination was provided with standard fluorescent lamps at a photosynthetic photon flux density of 50 to 60 mol of photons m Ϫ2 s Ϫ1 , which resulted in generation times of 15 to 16 h. Nitrogen or sulfur step-down was initiated by filtration on polyvinylidene difluoride membranes and resuspension of the cells in medium deprived of a combined-nitrogen or sulfur source, as described previously (10). Cultures of MP2 and MNtcA were maintained in the presence of 25 g of kanamycin/ml.…”

“…strain PCC 7942) (13) and S. elongatus PCC 7942 mutants MP2, lacking the P II signaling protein (glnB::aphII) (6), and MNtcA, lacking the NtcA protein (ntcA::aphII) (31). Cells were grown in liquid BG11 medium (28) at 30°C as described previously (10). When ammonium was used as a nitrogen source, the nitrate salt from BG11 was replaced by 5 mM NH 4 Cl and the medium was buffered to pH 8.0 with 5 mM HEPES.…”

Cyanobacteria in Scandinavian coastal waters — A potential source for biofuels and fatty acids?

“…Although the specific growth rate for A. flos-aquae was negative between Day 0 and Day 7 in all treatments, it is positive between Day 7 and Day 14. This indicates a longer acclimatization time for A. flos-aquae and it would have been interesting to continue the experiment (compare e.g., [59,78], Wulff et al, unpublished). D. lemmermannii had negative specific growth rate in all treatments throughout the experiment.…”

The Synechococcus Strain PCC 7942 glnN Product (Glutamine Synthetase III) Helps Recovery from Prolonged Nitrogen Chlorosis

“…Recently, it was shown that the complete depigmentation of cells of the obligate photoautotroph Synechococcus strain PCC 7942 is not a consequence of loss of cell viability but a specific acclimation process which enables the cells to survive for prolonged periods of nitrogen starvation (12). This acclimation process proceeds in three phases.…”

“…The rapid trimming and degradation of the phycobilisomes (phase 1) (2, 12) is followed by a gradual loss of chlorophyll a (Chl a) and intracellular proteins (phase 2). Finally, the cells lose all visible pigmentation and enter a form of dormancy (phase 3), from which they are able to reinitiate growth within 3 to 4 days following the addition of a combined nitrogen source (12).…”