Trade-Off between Growth and Carbohydrate Accumulation in Nutrient-Limited Arthrospira sp. PCC 8005 Studied by Integrating Transcriptomic and Proteomic Approaches

Abstract

Cyanobacteria have a strong potential for biofuel production due to their ability to accumulate large amounts of carbohydrates. Nitrogen (N) stress can be used to increase the content of carbohydrates in the biomass, but it is expected to reduce biomass productivity. To study this trade-off between carbohydrate accumulation and biomass productivity, we characterized the biomass productivity, biomass composition as well as the transcriptome and proteome of the cyanobacterium Arthrospira sp. PCC 8005 cultured under N-limiting and N-replete conditions. N limitation resulted in a large increase in the carbohydrate content of the biomass (from 14 to 74%) and a decrease in the protein content (from 37 to 10%). Analyses of fatty acids indicated that no lipids were accumulated under N-limited conditions. Nevertheless, it did not affect the biomass productivity of the culture up to five days after N was depleted from the culture medium. Transcriptomic and proteomic analysis indicated that de novo protein synthesis was down-regulated in the N-limited culture. Proteins were degraded and partly converted into carbohydrates through gluconeogenesis. Cellular N derived from protein degradation was recycled through the TCA and GS-GOGAT cycles. In addition, photosynthetic energy production and carbon fixation were both down-regulated, while glycogen synthesis was up-regulated. Our results suggested that N limitation resulted in a redirection of photosynthetic energy from protein synthesis to glycogen synthesis. The fact that glycogen synthesis has a lower energy demand than protein synthesis might explain why Arthrospira is able to achieve a similar biomass productivity under N-limited as under N-replete conditions despite the fact that photosynthetic energy production was impaired by N limitation.

The Multiple Functions of Common Microbial Carbon Polymers, Glycogen and PHB, during Stress Responses in the Non-Diazotrophic Cyanobacterium Synechocystis sp. PCC 6803

“…Significant amounts of glycogen are already detectable after one day, peaking around 3 days of nitrogen starvation, whereas PHB does not peak until after five days of the nitrogen-starvation conditions tested ( Lehmann and Wober, 1976 ; De Philippis et al, 1992 ; Miyake et al, 1997 ; Panda et al, 2006 ; Monshupanee and Incharoensakdi, 2014 ; Hauf et al, 2015 ). This temporal shift in the nitrogen response of the two carbon-polymer syntheses is in agreement with transcriptional data ( Krasikov et al, 2012 ; Huang et al, 2013 ; Kopf et al, 2014 ; Depraetere et al, 2015 ). A concomitant expression has only been shown for enzymes involved in glycogen degradation, such as the glycogen phosphorylase (GlgP2) and debranching enzyme (GlgX), as well as for PHB synthesis enzymes, such as ketothiolase (PhaA), acetyl-coenzyme A reductase (PhaB), and PHB synthase (PhaCE; Azuma et al, 2011 ; Osanai et al, 2013 ; Nakaya et al, 2015 ).…”

“…Even in 2-OGDH-containing bacteria and plants, the enzyme is almost always inhibited during nitrogen starvation, which leads in turn to a concomitant overflow of the carbon excess into either glycogen or PHB polymer synthesis, amino acid biosynthesis, or alternative TCA shunts (e.g., GABA shunt; Walshaw et al, 1997 ). Our comparative study of knockout mutants reveals unambiguously that the primary carbon excess (from terminating photosynthetic reactions and starting amino acid release by protein degradation ( Hasunuma et al, 2013 ; Depraetere et al, 2015 ) is mainly directed into glycogen synthesis and not into PHB synthesis ( Figure 4 ). Only blocks of glycogen synthesis in Synechocystis sp.…”

Glucosidase Inhibitors Screening in Microalgae and Cyanobacteria Isolated from the Amazon and Proteomic Analysis of Inhibitor Producing Synechococcus sp. GFB01

“…Then, performing manual curation, the proteins were classified into eight groups according to their function and gene ontology terms (Table S2). The group with the most proteins is the photosynthesis and carbon fixation with 56 proteins; this metabolism was more active in the complete medium with 53 proteins in this condition against 34 in stress, behavior verified in other cyanobacteria [105][106][107][108]. Among the 31 proteins common to the two conditions, we have two CpcG, one over expressed in BG-11 10%N and one under expressed in this condition, and this polypeptide linked to phycobilisome had its expression maintained in Synechocystis sp.…”

Influence of culture conditions on the production of extracellular polymeric substances (EPS) by Arthrospira platensis

“…According to Depraetere et al (2015), when the nitrate source is depleted, protein synthesis is reduced. In the present work, the highest protein concentrations, 7.05 ± 0.30 mg g −1 and 6.46 ± 0.20 mg g −1 , were observed for intermediate NaNO 3 concentrations, under conditions 5 (1.125 gL −1 of NaNO 3 and 600 μE m −2 s −1 ) and 8 (1.125 gL −1 of NaNO 3 and 1000 μE m −2 s −1 ), respectively.…”