Assessment of Polyhydroxybutyrate Production by Cyanobacteria Strains Isolated from Environmental Water Sources Using Secondary Treated Wastewater

Abstract

Five different strains of cyanobacteria were isolated from microbiome cultures obtained from environmental samples to test their polyhydroxybutyrate (PHB) production capacity. The objective was to discern the most productive strains and to find optimal conditions for polymer production. Cultures were set in both modified BG11 media (without nitrogen, phosphorus and inorganic carbon) and secondary effluent from treated urban wastewater during the PHB accumulation test. Both mediums were tested at different acetate concentrations (0g/L, 0.6g/L and 4g/L) in 50mL tubes. All tubes were inoculated with a biomass concentration of 0.4g/L and homogenized with nitrogen gas aeration under darkness conditions for seven days. Biomass quantity remained stable at 0.4g/L volatile suspended solids after the 7-day inoculation for all strains in every condition except for the Synechococcus sp. strain that diminished its biomass concentration to 0.28g/L after one week grown in secondary effluent. Results show that the optimal conditions for maximum (PHB) production are found in the strain of Synechocystis sp. isolated from a agricultural pond using modified BG-11 medium with a 0.6g/L acetate concentration, obtaining a PHB content of 3.1% in dry cellular weight. For all strains, secondary effluent diminished their polymer production. The maximum value of PHB content using secondary effluent was of 2.9% in dry cellular weight for Leptolyngbya sp. strain isolated from a river but with an acetate concentration of 4g/L. Finally, the data obtained can serve as a basis for creating bioplastics which act as biodegradable raw materials that are environmentally friendly.

Keywords: PHB, BG11 media, Secondary effluent