Insight in microalgal carbon flux under growth and stress conditions by biomass analysis

Claude Aflalo

Microalgal Biotechnology Laboratory, Institute for Agriculture and Biotechnology of Drylands, Institutes for Desert Research, Ben Gurion University, Sede Boqer Campus 84990 Israel

The production of alternative energy sources from algae is predominantly hampered by limited biological knowledge on the metabolism and control of building blocks formation for growth and of storage materials accumulation under stress. A working understanding needs to be developed and implemented to account for carbon flux from CO2 into protein (mostly growth), or carbohydrate and lipid (growth + storage), the latter classes being exploitable as potential sources for biofuel and biodiesel industrial production. A robust methodology for fast determination of total molecular classes in biomass has been developed, and found operational, independently of the organism species and/or its physiological status. The procedure is well suited for routine screening purposes and data acquisition for rapid analysis of carbon fluxes. Fresh algal biomass is hydrolyzed in acid releasing sugar monomers as well as free fatty acids and sterols further estimated by colorimetry. The rapid method has been validated against independent procedures. A preliminary analysis of algal cultures under various stress conditions indicate that (i) division stops; (ii) the dry mass/cell increases; (iii) a fast increase of the total carbohydrate/cell occurs, followed by total lipid/cell; (v) the ratio lipid:carbohydrate increases in correlation with that of carotenoid:chlorophyll. The later parameters together represent good indices for quantitative evaluation of the stress status in algal cultures. A mechanistic picture emerges in which any stress severely impairing of balanced growth result in an imbalance between the input (light absorbed) and the output (cell energy and reductive power). The coordinated cellular response is such that less light is absorbed (lower chlorophyll) and the cell metabolism is reprogrammed to dissipate excess energy and/or reductive equivalents, reinvested in storage materials (sugars or less oxidized oil), according to the ambient conditions, to reach a new steady balance.

e-mail address of presenting author: aflaloc@bgu.ac.il