Search NASA⌕ Search

Engineering topics

Ghirardi, Maria

Publications and source records attributed to Ghirardi, Maria.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Transcriptome and proteome analysis of nitrogen starvation responses in Synechocystis 6803 ΔglgC , a mutant incapable of glycogen storage

Molecular mechanisms that regulate carbon flux are poorly understood in algae. The ΔglgC mutant of the cyanobacterium Synechocystis sp. PCC 6803 is incapable of glycogen storage and displays an array of physiological responses under nitrogen starvation that are different from wild-type (WT). These include non-bleaching phenotype and the redirection of photosynthetically fixed carbon towards excreted organic acids (overflow metabolism) without biomass growth. To understand the role of gene/protein expression in these responses, we followed the time course of transcripts by genome-scale microarrays and proteins by shotgun proteomics in ΔglgC and WT cells upon nitrogen starvation. Compared to WT, the degradation of phycobilisome rod proteins was delayed and attenuated in the mutant, and the core proteins were less degraded; both contributed to the non-bleaching appearance despite the induction of nblA genes, suggesting the presence of a break in regulation of the phycobilisome degradation pathway downstream of nblA induction. The mutant displayed NtcA-mediated transcriptional response to nitrogen starvation, indicating that it is able to sense nitrogen status. Furthermore, some responses to nitrogen starvation appear to be stronger in the mutant, as shown by the increases in transcripts for the transcriptional regulator, rre37 , which regulates central carbon metabolism. Accordingly, multiple proteins involved in photosynthesis, central carbon metabolism, and carbon storage and utilization showed lower abundance in the mutant. Furthermore, these results indicate that the transition in the central carbon metabolism from growth to overflow metabolism in ΔglgC does not require increases in expression of the overflow pathway enzymes; the transition and non-bleaching phenotype are likely regulated instead at the metabolite level.

09 BIOMASS FUELS↗
DOE OSTI2015

Enhancing photo‐catalytic production of organic acids in the cyanobacterium S ynechocystis sp. PCC 6803 Δ glg C , a strain incapable of glycogen storage

Summary A key objective in microbial biofuels strain development is to maximize carbon flux to target products while minimizing cell biomass accumulation, such that ideally the algae and bacteria would operate in a photo‐catalytic state. A brief period of such a physiological state has recently been demonstrated in the cyanobacterium S ynechocystis sp. PCC 6803 Δ glgC strain incapable of glycogen storage. When deprived of nitrogen, the Δ glgC excretes the organic acids alpha‐ketoglutarate and pyruvate for a number of days without increasing cell biomass. This study examines the relationship between the growth state and the photo‐catalytic state, and characterizes the metabolic adaptability of the photo‐catalytic state to increasing light intensity. It is found that the culture can transition naturally from the growth state into the photo‐catalytic state when provided with limited nitrogen supply during the growth phase. Photosynthetic capacity and pigments are lost over time in the photo‐catalytic state. Reversal to growth state is observed with re‐addition of nitrogen nutrient, accompanied by restoration of photosynthetic capacity and pigment levels in the cells. While the overall productivity increased under high light conditions, the ratio of alpha‐ketoglutarate/pyruvate is altered, suggesting that carbon partition between the two products is adaptable to environmental conditions.

09 BIOMASS FUELS↗
DOE OSTI2011

NREL's Hydrogen Program

The research and development taking place today at the National Renewable Energy Laboratory (NREL) is paving the way for nature's most plentiful element—hydrogen—to power the next generation. NREL researchers are working to unlock the potential of hydrogen and to advance the fuel cell technologies that will power the automobiles, equipment, and buildings of tomorrow. Hydrogen and fuel cells are a fundamental part of the broader portfolio of renewable technologies that are moving our nation toward its goals of energy independence and sustainability.

13 HYDRO ENERGY↗