Cyanobacterial strain Synechocystis sp. GS-SphU with enhanced phosphorus uptake efficiency as potential agent for...

Phosphorus is a critical element for agricultural production. Its recovery from wastewater represents an important strategy for conserving this non-renewable resource, a substantial fraction of which is lost following field application. Wastewater-derived phosphorus contributes to the disruption of aquatic and coastal ecosystems, primarily through the promotion of algal blooms. The conversion of spent biomass into biochar may allow to make a phosphorus-enriched product which can be used to recycle phosphorus. The present study investigates a modified strain of cyanobacterium Synechocystis sp. GS-SphU characterized by enhanced phosphorus uptake, as well as a potential approach to utilizing its biomass in biochar production. Synechocystis sp. GS-SphU was found to absorb more than 99% of phosphorus from the medium and accumulates 3 times more phosphorus compared to the unmodified strain. Transmission electron microscopy shows that both unmodified and modified strains accumulate phosphorus as large polyphosphate granules while the modified strain additionally exhibited the accumulation of numerous small granules distributed throughout the cytoplasm. The addition of 10% dry biomass of Synechocystis sp. GS-SphU to the raw material for biochar preparation increases the phosphorus content of the final product by 2.14-3.56 times, whereas the addition of unmodified strain leads to the increase in phosphorus only by 1.3-1.96 times. The resulting phosphorus-enriched biochar demonstrates considerable potential as an agricultural biofertilizer, thereby contributing to a closed-loop system for phosphorus recovery and reuse from wastewater.