Proteomic and cellular views of Arthrospira sp. PCC 8005 adaptation to nitrogen depletion

Abstract

Cyanobacteria are photosynthetic prokaryotes that play a crucial role in the Earth's nitrogen and carbon cycles. Nitrogen availability is one of the most important factors in cyanobacterial growth. Interestingly, filamentous non-diazotrophic cyanobacteria, such as Arthrospira sp. PCC 8005, have developed survival strategies that enable them to adapt to nitrogen deprivation. Metabolic studies recently demonstrated a substantial synthesis and accumulation of glycogen derived from amino acids during nitrogen starvation. Nevertheless, the regulatory mechanism of this adaptation is poorly understood. To the best of our knowledge, this study is the first proteomic and cellular analysis of Arthrospira sp. PCC 8005 under nitrogen depletion. Label-free differential proteomic analysis indicated the global carbon and nitrogen reprogramming of the cells during nitrogen depletion as characterized by an upregulation of glycogen synthesis and the use of endogenous nitrogen sources. The degradation of proteins and cyanophycin provided endogenous nitrogen when exogenous nitrogen was limited. Moreover, formamides, cyanates and urea were also potential endogenous nitrogen sources. The transporters of some amino acids and alternative nitrogen sources such as ammonium permease 1 were induced under nitrogen depletion. Intriguingly, although Arthrospira is a non-diazotrophic cyanobacterium, we observed the upregulation of HetR and HglK proteins, which are involved in heterocyst differentiation. Moreover, after a long period without nitrate, only a few highly fluorescent cells in each trichome were observed, and they might be involved in the long-term survival mechanism of this non-diazotrophic cyanobacterium under nitrogen deprivation.

Molecular investigation of the radiation resistance of edible cyanobacterium Arthrospira sp. PCC 8005

“…Photosynthesis and carbon fixation shutdown was also reported for Arthrospira in response to other stress factors such as nitrogen depletion stress (Deschoenmaeker et al. ), but was never before demonstrated in such detail, at RNA level. Only physiological examinations were reported and there are no transcriptomic data available for Arthrospira in response to UV stress (Wu et al.…”

“…) or nitrogen deficiency) (Deschoenmaeker et al. ), which makes their response to IR rather unique and peculiar. It is possible that this set of genes may play an important role in the high radiation resistance of Arthrospira sp .…”

Harvesting carbohydrate-rich Arthrospira platensis by spontaneous settling

“…Arthrospira responds to N stress by reducing protein synthesis (which requires large amounts of N) and redirecting photosynthesis products towards production of storage carbohydrates (Hasunuma et al, 2013). Recent evidence suggests Arthrospira may even convert proteins into storage carbohydrates during N stress (Deschoenmaeker et al, 2014;Hasunuma et al, 2013). A previous study has also observed spontaneous flocculation of Arthrospira, but under P stress rather than N stress (Markou et al, 2012).…”

Nitrogen chlorosis in unicellular cyanobacteria – a developmental program for surviving nitrogen deprivation

“…3), as shown for the unicellular strains of species S. elongatus (Görl et al, 1998;Sauer et al, 2001), Synechocystis (Richaud et al, 2001;Hauf et al, 2015) and the filamentous Arthrospira sp. PCC 8005 (Deschoenmaeker et al, 2014;. At the end of this process, the cells, which are characterized by substantial internal morphological changes, reside in a state of extremely reduced metabolic activity, but most cells retain viability.…”