Improvement of the Cd removal efficiency of a filamentous cyanobacterium Leptolyngbya sp. XZ1 through co-culture with Bacillus sp. S1

The co-culture of cyanobacteria and heterotrophic bacteria can utilize the advantages of both bacteria, effectively remove pollutants and relieve the feedback inhibition effect in algae culture; however, little information is available in heavy metal removal. In this study, a filamentous cyanobacterium, Leptolyngbya sp. XZ1, isolated from biological soil crusts and four heterotrophic bacterial strains, namely, Y3, Y4, S1 and T2, isolated from the phycosphere were co-inoculated into BG-11 media containing Cd. Amongst co-culture systems, Leptolyngbya + S1 showed the highest Cd removal efficiencies of 93.2%, 71.8%, 60.7%, 56.8% and 41.0% at initial Cd concentrations of 2, 5, 10, 20 and 50 mg L−1, respectively. In this co-culture system, Cd adsorbed on the cell wall was increased by 42.8%, 52.9%, 50.0% and 22.6%, and the intracellular Cd was decreased by 37.9%, 37.0%, 51.0% and 50.6% at initial Cd concentrations of 5, 10, 20 and 50 mg L−1, respectively, compared with the Leptolyngbya monoculture. Under Cd stress, the biomass, extracellular polymeric substances (EPS)-polysaccharides and photosystem II activity of Leptolyngbya sp. XZ1 were increased by co-culture with Bacillus sp. S1. In addition, the Cd stress on Leptolyngbya was alleviated by co-culture with S1 as proven by the superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, scanning electron microscopy (SEM) images, soluble protein content and SDS-PAGE analysis. Results indicated that the cyanobacteria-heterotrophic bacteria co-culture system can be used as an effective bioremediation method to remove heavy metals from aqueous solution.