Abstract
Probiotic-derived polyphosphates have attracted interest as potential therapeutic agents to improve intestinal health. The current study discovered the intracellular accumulation of polyphosphates in a marine cyanobacterium Synechococcus sp. PCC 7002 as nano-sized granules. The maximum accumulation of polyphosphates in Synechococcus sp. PCC 7002 was found at the late logarithmic growth phase when the medium contained 0.74 mM of KH2PO4, 11.76 mM of NaNO3, and 30.42 mM of Na2SO4. Biogenic polyphosphate nanoparticles (BPNPs) were obtained intact from the algae cells by hot water extraction, and were purified to remove the organic impurities by Sephadex G-100 gel filtration. By using 100 kDa ultrafiltration, BPNPs were fractionated into the larger and smaller populations with diameters ranging between 30–70 nm and 10–30 nm, respectively. 4′,6-diamidino-2-phenylindole fluorescence and orthophosphate production revealed that a minor portion of BPNPs (about 14–18%) were degraded during simulated gastrointestinal digestion. In vitro studies using lipopolysaccharide-activated RAW264.7 cells showed that BPNPs inhibited cyclooxygenase-2, inducible nitric oxide (NO) synthase expression, and the production of proinflammatory mediators, including NO, tumor necrosis factor-α, interleukin-6, and interleukin-1β through suppressing the Toll-like receptor 4/NF-κB signaling pathway. Overall, there is promise in the use of the marine cyanobacterium Synechococcus sp. PCC 7002 to produce BPNPs, an anti-inflammatory postbiotic.
Highlights
Inorganic polyphosphates are polyanionic linear polymers composed of three to several hundred high-energy phosphoanhydride-bonded orthophosphate residues
Energy dispersive spectroscopy (EDS) of the yellow circle region in Figure 1b revealed that these granules contained abundant oxygen and phosphorus with the oxygen/phosphorus molar ratio calculated to be about three, corresponding to that in polyPs (Figure 1c). 40,6-diamidino-2-phenylindole (DAPI) is frequently used to quantify and visualize polyPs due to its characteristic specific green fluorescence with polyPs [20]
According to the reported to be negligible [37]. It seems that the gastric acid-catalyzed hydrolysis of polyPs results of DAPI fluorescence and orthophosphate production (Figure 5a,b), only a minor portion accounted for the Gastrointestinal Digestion (GID)-induced partial degradation of Biogenic polyphosphate nanoparticles (BPNPs)
Summary
Inorganic polyphosphates (polyPs) are polyanionic linear polymers composed of three to several hundred high-energy phosphoanhydride-bonded orthophosphate residues. Many marine cyanobacteria, which are autotrophic on natural sunlight and CO2 , accumulate large amounts of polyP granules within cells to combat the recurrent phosphorus starvation in the ocean [14]. They seem to be promising “photobioreactors” to produce polyPs in an energy and freshwater-saving way. Synechococcus 7002 survives a wide range of salt concentrations and temperatures, and can live photoautotrophically, mixotrophically, or heterotrophically [18] This strain naturally captures foreign linear double-stranded DNA and integrates them into its own genome by homologous recombination [19]. We optimized the fermentation conditions for the production of BPNPs by Synechococcus 7002, and characterized the particle, digestibility, and anti-inflammatory properties of BPNPs
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