Phosphorus uptake and growth of Tolypothrix tenuis: A potential bioremediation agent for eutrophic waters

Eutrophication, driven by excessive anthropogenic nutrients inputs, remains a major environmental concern in freshwater ecosystems worldwide. This study evaluates the potential of controlled photoautotrophic cultivation of the filamentous cyanobacterium Tolypothrix tenuis as a bioremediation agent for the removal of bioavailable phosphorus (P) from eutrophic waters. Batch cultivations were conducted to assess the effects of inoculum concentration, inoculum P-starvation, temperature, photosynthetic photon flux density (PPFD), and photoperiod on P-uptake dynamics (i), intracellular P accumulation (ii), and biomass productivity (iii). P concentrations in the medium were quantified as soluble reactive P (SRP) using the molybdate-reactive method, representing the fraction most directly linked to eutrophication processes. In general, the results show that biomass growth and P-uptake are not strictly coupled processes resulting in variations in intracellular P-content. Extended P-starvation markedly reduced intracellular P-content but enhanced subsequent P-uptake rates as well as resulting intracellular P-content, demonstrating the induction of luxury P-uptake. It was found out, that temperature strongly influenced both biomass productivity and P-uptake rate, while PPFD (150–350 μmol/m 2 /s) primarily affected growth without substantially altering P-uptake. Across all the experimental temperatures (11–30 °C), extracellular SRP concentrations decreased below 0.05 mg P /L, a commonly used eutrophic threshold, and remained at oligotrophic levels for up to three months without detectable phosphorus release. Overall, T. tenuis exhibited high P-removal efficiency. Moreover, the phosphorus-enriched biomass produced in this process represents a potential P-recycling bioresource that warrants further evaluation for agricultural reuse. • Extended P-starvation enhanced uptake and induced luxury P accumulation. • Growth and P-uptake rates were not strictly coupled under tested conditions. • T. tenuis showed high metabolic flexibility exploitable in bioremediation. • P-content of Tolypothrix tenuis varied between 3.5 and 21.6 mg P /g DW .