Can a Cyanobacterium Clean the Amazon Waters?

What would happen if a tiny photosynthetic organism could turn the Amazon's dirty water into useful resources? A Peruvian research team tested the cyanobacterium Synechococcus sp., isolated from the Amazon basin, to clean urban wastewater. The strain was grown in different dilutions of effluent (25%, 50%, 75% and 100%) taken from Lake Moronacocha. The most striking result came with 25% wastewater: specific growth reached 22.8 × 10⁻² µ·day⁻¹, with a biomass increase of 393.2%, surpassing the standard BG‑11 medium. In these conditions ammonium removal was 95.4%, almost total, and phycocyanin production rose to 33.6 µg/mg, 56% higher than the control. When wastewater concentration increased, both growth rate and removal efficiency dropped. Biochemical analysis showed that at higher concentrations proteins decreased while lipids rose, hinting at a shift toward biofuel precursors. These data suggest Synechococcus sp. can both purify water and generate valuable biomass, fitting a circular bioeconomy model for the Amazon region.

Synechococcus sp. is a photosynthetic cyanobacterium belonging to the picocyanobacteria group, characterized by a small cell size (1‑2 µm) and rapid response to environmental changes. In this study, growth was monitored by measuring absorbance at 750 nm, allowing calculation of the specific growth rate (µ) using a Monod equation modified to include ammonium (NH₄⁺) concentration as the limiting substrate. Kinetic analysis revealed an affinity constant (Kₛ) of about 0.12 mg L⁻¹ for NH₄⁺, indicating high uptake capacity even at low concentrations. Ammonium removal occurred mainly through cellular assimilation, followed by incorporation into amino acids and proteins, as shown by increased protein content at lower wastewater concentrations. However, at higher concentrations of organic and inorganic pollutants, lipid synthesis pathways were activated, likely as an oxidative stress response, leading to triacylglycerol accumulation. Phycocyanin production, a biliprotein pigment with antioxidant properties, peaked at 33.6 µg mg⁻¹ biomass, making the biomass suitable for nutraceutical applications. From a circular bioeconomy perspective, the biomass can be fractionated: proteins for feed, lipids for biodiesel, and phycocyanin for dietary supplements or natural dyes. Metabolomic profiling via mass spectrometry revealed medium‑chain fatty acids (C₈‑C₁₂), desirable for low‑viscosity biofuels. Moreover, Synechococcus sp.’s ability to grow under natural light with a 12‑hour photoperiod reduces energy costs compared to closed photobioreactors. Integrating this microorganism into municipal wastewater treatment plants could thus provide dual benefits: nutrient (NH₄⁺, PO₄³⁻) removal and generation of high‑value biomass, helping close nutrient loops in the Amazon region. Future research should explore resistance to emerging contaminants (pharmaceuticals, microplastics) and optimize operational parameters (pH, temperature, light flux) to maximize yields of valuable products.