Abstract
Microalgae and cyanobacteria are promising organisms for sustainable biofuel production, but several challenges remain to make this economically viable, including identification of optimized strains with high biomass productivity. Here we report on a novel methodology for the label-free screening and sorting of cyanobacteria and microalgae in a microdroplet platform. We show for the first time that chlorophyll fluorescence can be used to measure differences in biomass between populations of picoliter microdroplets containing different species of cyanobacteria, Synechocystis PCC 6803 and Synechococcus PCC 7002, which exhibit different growth dynamics in bulk culture. The potential and robustness of this label-free screening approach is further demonstrated by the screening and sorting of cells of the green alga Chlamydomonas reinhardtii encapsulated in droplets.
Highlights
Cyanobacteria Synechocystis PCC 6803 and Synechococcus PCC 7002 were selected due to their different growth rates and final cell densities observed in bulk culture experiments (Figure 2A)
The results confirmed that Synechococcus PCC 7002 grew faster, generating significantly higher biomass in an average droplet than Synechocystis PCC 6803 after 4 days (Figure 2 C)
Synechocystis PCC 6803 and Synechococcus PCC 7002, whose growth rates differ in bulk cultures, the system could discriminate between the cells of the two species after 4 days of growth in the microdroplets
Summary
Article sort a mixed population of E. coli cells based on β-galactosidase enzymatic activity, which transformed a nonfluorescent βgalactoside substrate into fluorescein. Of particular note is that cells from both the “positive” and “negative” collection channels were motile in droplets after sorting, as the encapsulated cells can be seen swimming around (Figure S4, Supporting Information). Encapsulated C. reinhardtii grown in nitrogen limited medium has much lower chlorophyll fluorescence levels than those grown in 1 N TAP (Figure 5A).This feature is a characteristic of microalgal cells subjected to nitrogen stress concomitant with an induction in neutral lipid (TAG) production.[41] Droplets with low chlorophyll cells were reinjected into a microdroplet sorting chip as described in the previous section. Insufficient droplets were obtained in the positive channel to allow for reinjection and reimaging
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