Overproduction, purification, and characterization of nanosized polyphosphate bodies from Synechococcus sp. PCC 7002

BACKGROUND Inorganic polyphosphate bodies (PPB) have recently been linked to a variety of functions in mammalian cells. To improve the yield of PPB from Synechococcus sp. PCC 7002 and characterize its form, in this study, a recombinant plasmid containing a polyphosphate kinase (ppk) gene was generated and transformed into Synechococcus sp. PCC 7002. RESULTS PPB separated by Sephadex G-100 was characterized and added to polarized human intestinal epithelial (Caco-2) cells, and the absorption effect was assessed. The ppk gene was stably expressed by induction with 1 μM nickel, and the resulting PPB yield from Synechococcus sp. PCC 7002 cells increased by 89.66%. Transmission electron microscopy and dynamic light scattering analyses showed that PPB from these cells were nanosized, ranging from a few to approximately 100 nanometres in diameter. PPB can be taken up by Caco-2 cells and are mainly distributed around lipid droplets. CONCLUSIONS We determined that PPB can be overproduced in Synechococcus sp. PCC 7002 and that the resulting PPB were well absorbed by Caco-2 cells. Microalgae provide a promising "cell factory" for PPB production.