In vivo 31P and multilabel 13C NMR measurements for evaluation of plant metabolic pathways

Development of a small-scale bioreactor: application to in vivo NMR measurement

A perfused bioreactor allowing in vivo NMR measurement was developed and validated for Eschscholtzia californica cells. The bioreactor was made of a 10-mm NMR tube. NMR measurement of the signal-to-noise ratio was optimized using a sedimented compact bed of cells that were retained in the bioreactor by a supporting filter. Liquid medium flow through the cell bed was characterized from a mass balance on oxygen and a dispersive hydrodynamic model. Cell bed oxygen demand for 4 h perfusion required a minimal medium flow rate of 0.8 mL/min. Residence time distribution assays at 0.8-2.6 mL/min suggest that the cells are subjected to a uniform nutrient environment along the cell bed. Cell integrity was maintained for all culture conditions since the release of intracellular esterases was not significant even after 4 h of perfusion. In vivo NMR was performed for (31)P NMR and the spectrum can be recorded after only 10 min of spectral accumulation (500 scans) with peaks identified as G-6P, F-6P, cytoplasmic Pi, vacuolar Pi, ATP(gamma) and ADP(beta), ATP(alpha) and ADP(alpha), NADP and NDPG, NDPG and ATP(beta). Cell viability was shown to be maintained as (31)P chemical shifts were constant with time for all the identified nuclei, thus suggesting constant intracellular pH.

Critical influence ofEschscholzia californica cells nutritional state on secondary metabolite production

In this study, we investigated the influence of initial internal nutrient concentrations at the time of elicitation on the ability of Eschscholzia californica (EC) cells to produce alkaloids. Three EC cell suspensions cultivated in culture media differing in their PO4(3-) and NO3- contents were sampled daily for 12 days and analyzed for extracellular and intracellular nutrient concentrations. The ability of the cells to produce alkaloids was tested along the three cell suspension cultures. Sampled cells were then further cultured for 7 days in a production medium containing the elicitor and an extraction resin. The alkaloid production of the cells was measured 7 days post-elicitation. In the low-N medium, starch, glucose, and phosphate contents in the biomass was increased by 470, 1624 and 70%, respectively, 10 days after inoculation compared to the control culture in standard B5 medium. Cell concentration was significantly reduced from 10.3 to 8.6 millions cell/mL on this low-N medium compared to the control, nevertheless alkaloid production was multiplied by 39 at day 10 when cells were elicited. Cells grown on the low-N or low-P media accumulated 83% and 188% more carbon, respectively, than control cells at the end of the culture. This intracellular C was mainly stored in the form of starch in low-P medium and both in the form of starch and glucose in the low-N medium. The ability of EC cells to produce alkaloids upon elicitation was shown to be strongly dependent on the initial intracellular C and P content at the time of elicitation. This suggests that reproducibility and productivity during EC cell culture could be enhanced by manipulating the intracellular C and P content at the time of elicitation.

Carbohydrate cycling in micro-organisms: what can (13)C-NMR tell us?

The extension of (13)C-nuclear magnetic resonance (NMR) techniques to study cellular metabolism over recent years has provided valuable data supporting the occurrence, diversity and extent of carbon cycling in the carbohydrate metabolism of micro-organisms. The occurrence of such cycles, resulting from the simultaneous operation of different and sometimes opposite individual steps, is inherently related to the network organisation of cellular metabolism. These cycles are tentatively classified here as 'reversibility', 'metabolic' and 'substrate' cycles on the basis of their balance in carbon and cofactors. Current hypotheses concerning the physiological relevance of carbohydrate cycles are discussed in light of the (13)C-NMR data. They most likely represent system-level mechanisms for coherent and timely partitioning of carbon resources to fit with the various biosynthetic, energetic or redox needs of cells and/or additional strategies in the adaptive capacity of micro-organisms to face variation in environmental conditions.

Relevance and isotopic assessment of hexose-6-phosphate recycling in micro-organisms

Some pathways of hexose-6-phosphate recycling--those involving a breakdown of the hexose skeleton--through carbohydrate metabolism of micro-organisms were analyzed for both metabolic and isotopic effects. Two modes of recycling were proposed based on the degree of alteration of the hexose molecule through the catabolic part of the cycle. Simulated operation of most of these pathways resulted in increased synthesis of hexose-6-phosphate and NADPH, and reduced the NADH and moreover the ATP synthesis within the carbohydrate metabolism. A basic model for the quantitative assessment by means of isotopic studies of the processes of hexose-6-phosphate recycling is presented. The model was initially designed for the study of micro-organisms producing polysaccharides, but it can be extended to other situations.

Plant 'hairy root' culture

Due to their fast growth rates and biochemical stability, 'hairy root' cultures remain unsurpassed as the choice for model root systems and have promise as a bioprocessing system. Applications are wide-ranging, from the production of natural products and foreign proteins to a model for phytoremediation of organic and metal contaminants. Hairy roots will have a continuing role as an experimental model in plant metabolic engineering.