Figure 6. Carbon storage enhances propagation of 12B01 on alginate polysaccharide.

A) Growth curves of high-PHA and low-PHA 12B01 populations on alginate oligosaccharides. Black, high-PHA population; grey, low-PHA population. Bars indicate standard error, n=3. B) Fraction of total cell population from A, binned by the mean intensity of Nile Red staining per cell in arbitrary fluorescence units. Nile Red staining is taken as a measurement of PHA storage within cells. C) Growth of high-PHA and low-PHA populations on alginate polysaccharide. Populations were grown alone, or as admixtures. H+H, a 1:1 mixture of mKate and eGFP-expressing high-PHA populations; L+L a 1:1 mixture of low-PHA expressing populations; H+L mixtures of high-PHA and low-PHA populations. All cultures were inoculated with 1.3*10⁶ cells/mL +/− 0.7*10⁶ cells/mL. D) Composition of cultures containing eGFP and mKate admixtures. RCI, relative competitive index, or the initial ratio of eGFP/mKate cells divided by the final ratio or eGFP/mKate cells. H, high PHA; L, low PHA; pink, mKate; green, eGFP. E) Proposed ‘reproductive cycles’ supporting cooperative growth of 12B01 growth on alginate. Cells form clonal clusters. Local density promotes growth on alginate polysaccharide in a carbon-limited environment. As clusters grow, they phenotypically differentiate into ‘shell’ (grey) and ‘core’(red) sub-populations in response to resource gradients. Clusters rupture, releasing carbon-storing ‘core’ sub-population which can propagate to form new clonal clusters.