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

Polyphosphate accumulation in microalgae and cyanobacteria: recent advances and opportunities for phosphorus upcycling

Phosphorus (P) must continuously be added to soils as it is lost in the food chain and via leaching. Unfortunately, the mining and import of P to produce fertiliser is unsustainable and costly. Potential solutions to the global issues of P rock depletion and pollution lie in microalgae and cyanobacteria. With an ability to intracellularly store P as polyphosphates, microalgae and cyanobacteria could provide the basis for removing P from water streams, thereby mitigating eutrophication, and even enabling P recovery as P-rich biomass. Metabolic engineering or changes in growing conditions have been demonstrated to improve P removal and recovery by triggering polyphosphates synthesis in the laboratory. This now needs to be replicated at full scale.

Is Genetic Engineering a Route to Enhance Microalgae-Mediated Bioremediation of Heavy Metal-Containing Effluents?

Contamination of the biosphere by heavy metals has been rising, due to accelerated anthropogenic activities, and is nowadays, a matter of serious global concern. Removal of such inorganic pollutants from aquatic environments via biological processes has earned great popularity, for its cost-effectiveness and high efficiency, compared to conventional physicochemical methods. Among candidate organisms, microalgae offer several competitive advantages; phycoremediation has even been claimed as the next generation of wastewater treatment technologies. Furthermore, integration of microalgae-mediated wastewater treatment and bioenergy production adds favorably to the economic feasibility of the former process-with energy security coming along with environmental sustainability. However, poor biomass productivity under abiotic stress conditions has hindered the large-scale deployment of microalgae. Recent advances encompassing molecular tools for genome editing, together with the advent of multiomics technologies and computational approaches, have permitted the design of tailor-made microalgal cell factories, which encompass multiple beneficial traits, while circumventing those associated with the bioaccumulation of unfavorable chemicals. Previous studies unfolded several routes through which genetic engineering-mediated improvements appear feasible (encompassing sequestration/uptake capacity and specificity for heavy metals); they can be categorized as metal transportation, chelation, or biotransformation, with regulation of metal- and oxidative stress response, as well as cell surface engineering playing a crucial role therein. This review covers the state-of-the-art metal stress mitigation mechanisms prevalent in microalgae, and discusses putative and tested metabolic engineering approaches, aimed at further improvement of those biological processes. Finally, current research gaps and future prospects arising from use of transgenic microalgae for heavy metal phycoremediation are reviewed.

Fixing the Broken Phosphorus Cycle: Wastewater Remediation by Microalgal Polyphosphates

Phosphorus (P), in the form of phosphate derived from either inorganic (Pi) or organic (Po) forms is an essential macronutrient for all life. P undergoes a biogeochemical cycle within the environment, but anthropogenic redistribution through inefficient agricultural practice and inadequate nutrient recovery at wastewater treatment works have resulted in a sustained transfer of P from rock deposits to land and aquatic environments. Our present and near future supply of P is primarily mined from rock P reserves in a limited number of geographical regions. To help ensure that this resource is adequate for humanity's food security, an energy-efficient means of recovering P from waste and recycling it for agriculture is required. This will also help to address excess discharge to water bodies and the resulting eutrophication. Microalgae possess the advantage of polymeric inorganic polyphosphate (PolyP) storage which can potentially operate simultaneously with remediation of waste nitrogen and phosphorus streams and flue gases (CO2, SOx, and NOx). Having high productivity in photoautotrophic, mixotrophic or heterotrophic growth modes, they can be harnessed in wastewater remediation strategies for biofuel production either directly (biodiesel) or in conjunction with anaerobic digestion (biogas) or dark fermentation (biohydrogen). Regulation of algal P uptake, storage, and mobilization is intertwined with the cellular status of other macronutrients (e.g., nitrogen and sulphur) in addition to the manufacture of other storage products (e.g., carbohydrate and lipids) or macromolecules (e.g., cell wall). A greater understanding of controlling factors in this complex interaction is required to facilitate and improve P control, recovery, and reuse from waste streams. The best understood algal genetic model is Chlamydomonas reinhardtii in terms of utility and shared resources. It also displays mixotrophic growth and advantageously, species of this genus are often found growing in wastewater treatment plants. In this review, we focus primarily on the molecular and genetic aspects of PolyP production or turnover and place this knowledge in the context of wastewater remediation and highlight developments and challenges in this field.

Polyphosphate: A Multifunctional Metabolite in Cyanobacteria and Algae

Polyphosphate (polyP), a polymer of orthophosphate (PO4 3-) of varying lengths, has been identified in all kingdoms of life. It can serve as a source of chemical bond energy (phosphoanhydride bond) that may have been used by biological systems prior to the evolution of ATP. Intracellular polyP is mainly stored as granules in specific vacuoles called acidocalcisomes, and its synthesis and accumulation appear to impact a myriad of cellular functions. It serves as a reservoir for inorganic PO4 3- and an energy source for fueling cellular metabolism, participates in maintaining adenylate and metal cation homeostasis, functions as a scaffold for sequestering cations, exhibits chaperone function, covalently binds to proteins to modify their activity, and enables normal acclimation of cells to stress conditions. PolyP also appears to have a role in symbiotic and parasitic associations, and in higher eukaryotes, low polyP levels seem to impact cancerous proliferation, apoptosis, procoagulant and proinflammatory responses and cause defects in TOR signaling. In this review, we discuss the metabolism, storage, and function of polyP in photosynthetic microbes, which mostly includes research on green algae and cyanobacteria. We focus on factors that impact polyP synthesis, specific enzymes required for its synthesis and degradation, sequestration of polyP in acidocalcisomes, its role in cellular energetics, acclimation processes, and metal homeostasis, and then transition to its potential applications for bioremediation and medical purposes.

Effect of microalgae as iron supplements on iron-deficiency anemia in rats

Microalgae are functional iron nutritive fortifiers that can supply more intestinal nanosized iron.

Biogenic Polyphosphate Nanoparticles from Synechococcus sp. PCC 7002 Exhibit Intestinal Protective Potential in Human Intestinal Epithelial Cells In Vitro and Murine Small Intestine Ex Vivo

Polyphosphates are one of the active compounds from probiotics to maintain gut health. The current research extracted and purified intact biogenic polyphosphate nanoparticles (BPNPs) from Synechococcus sp. PCC 7002 cells. BPNPs were near-spherical anionic particles (56.9 ± 15.1 nm) mainly composed of calcium and magnesium salt of polyphosphate and were colloidally stable at near-neutral and alkaline pH. BPNPs survived gastrointestinal digestion in mice and could be absorbed and transported by polarized Caco-2 cell monolayers. They dose-dependently increased the tightness of intercellular tight junction and the expression of claudin-4, occludin, zonula occludens-1, and heat shock protein 27 in Caco-2 cell monolayers. BPNPs also effectively attenuated H₂O₂-induced cell death, plasma membrane impairment, and intracellular superoxide production in NCM460 cells. In addition, they conferred resistance to H₂O₂-induced barrier disruption in freshly excised mouse small intestine. Our results suggest that BPNPs are a promising postbiotic nanomaterial with potential applications in gut health maintenance.