A novel association by Rhodospirillum rubrum and Rhodobacter capsulatus for bioremediation of heavy metals from aqueous solutions

Bioremediation is a promising method for removing heavy metals in contaminated effluents. Using several microorganisms, the process can provide efficient treatment, resulting in reduced waste generation, all while promoting sustainability. The current work evaluated the potential of the novel assembly by Rhodospirillum rubrum and Rhodobacter capsulatus to remove hexavalent chromium, total chromium, cadmium, and lead. In addition, photosynthetic pigment (bacteriochlorophyll-a and carotenoids) production and biomass increment were verified. A composite central design (CCD) was proposed to obtain models describing the behavior of the initial concentration of chromium, cadmium, and lead (independent variables). In the experiments described at the central point by the CCD, the co-culture (R. capsulatus: R. rubrum) was inoculated in 500 mL Erlenmeyer flasks containing an effluent consisting of RCV medium with heavy metals (20 mg/L Cr⁶⁺, 10 mg/L Cd²⁺ and 10 mg/L Pb²⁺). With a light intensity of 5760 lx and a biological cycle of 216 h, the maximum removals were 83% for total chromium, 30% for cadmium, and 80% for lead. Under these conditions, the biomass increased by 68% compared to the initial value (1.0 g/L), even in a highly toxic effluent.