Responses of Synechocystis sp. PCC 6803 to total dissolved solids in long-term continuous operation of a photobioreactor

Direct membrane-carbonation photobioreactor producing photoautotrophic biomass via carbon dioxide transfer and nutrient removal

An advanced-material photobioreactor, the direct membrane-carbonation photobioreactor (DMCPBR), was tested to investigate the impact of directly submerging a membrane carbonation (MC) module of hollow-fiber membranes inside the photobioreactor. Results demonstrate that the DMCPBR utilized over 90% of the supplied CO2 by matching the CO2 flux to the C demand of photoautotrophic biomass growth. The surface area of the submerged MC module was the key to control CO2 delivery and biomass productivity. Tracking the fate of supplied CO2 explained how the DMCPBR reduced loss of gaseous CO2 while matching the inorganic carbon (IC) demand to its supply. Accurate fate analysis required that the biomass-associated C include soluble microbial products as a sink for captured CO2. With the CO2 supply matched to the photosynthetic demand, light attenuation limited the rate microalgal photosynthesis. The DMCPBR presents an opportunity to improve CO2-deliver efficiency and make microalgae a more effective strategy for C-neutral resource recovery.

Selective carotenoid accumulation by varying nutrient media and salinity in Synechocystis sp. CCNM 2501

Nutrients are the deciding factors in the biological production of bioactive compounds. Various growth media like BG11, Zarrouk's and Chu's 10 were studied for carotenoid production in Synechocystis sp. CCNM 2501. Maximum carotenoid content (dry weight basis) was found in Zarrouk's medium (ZM, 7.99mgg(-1)) followed by BG11 (5.13mgg(-1)). Echinenone content was 4 times higher in ZM (3.81mgg(-1)) as compared to BG11 (0.95mgg(-1)) and Chu's 10 (0.77mgg(-1)). Being an economical medium, BG11 was selected for carotenoid production. Further, increase in salinity from 0 to 0.2M in BG11 medium increases total carotenoid content from 5.82 to 7.05mgg(-1) and later it declines to 6.23mgg(-1) (1M). 3 times more β-carotene is produced at 1M salinity as compared to control BG11. The variation in carotenoid composition with change in nutrients/salinity can be a good strategy to enhance certain targeted carotenoids.

Lipid production in association of filamentous fungi with genetically modified cyanobacterial cells

BACKGROUND

Numerous strategies have evolved recently for the generation of genetically modified or synthetic microalgae and cyanobacteria designed for production of ethanol, biodiesel and other fuels. In spite of their obvious attractiveness there are still a number of challenges that can affect their economic viability: the high costs associated with (1) harvesting, which can account for up to 50 % of the total biofuel's cost, (2) nutrients supply and (3) oil extraction. Fungal-assisted bio-flocculation of microalgae is gaining increasing attention due to its high efficiency, no need for added chemicals and low energy inputs. The implementation of renewable alternative carbon, nitrogen and phosphorus sources from agricultural wastes and wastewaters for growing algae and fungi makes this strategy economically attractive.

RESULTS

This work demonstrates that the filamentous fungi, Aspergillus fumigatus can efficiently flocculate the unicellular cyanobacteria Synechocystis PCC 6803 and its genetically modified derivatives that have been altered to enable secretion of free fatty acids into growth media. Secreted free fatty acids are potentially used by fungal cells as a carbon source for growth and ex-novo production of lipids. For most of genetically modified strains the total lipid yields extracted from the fungal-cyanobacterial pellets were found to be higher than additive yields of lipids and total free fatty acids produced by fungal and Synechocystis components when grown in mono-cultures. The synergistic effect observed in fungal-Synechocystis associations was also found in bioremediation rates when animal husbandry wastewater was used an alternative source of nitrogen and phosphorus.

CONCLUSION

Fungal assisted flocculation can complement and assist in large scale biofuel production from wild-type and genetically modified Synechocystis PCC 6803 strains by (1) efficient harvesting of cyanobacterial cells and (2) producing of high yields of lipids accumulated in fungal-cyanobacterial pellets.