Structural and functional bacterial biodiversity in a copper, zinc and nickel amended bioreactor: shotgun metagenomic study.

BACKGROUND

At lower concentrations copper (Cu), zinc (Zn) and nickel (Ni) are trace metals essential for some bacterial enzymes. At higher concentrations they might alter and inhibit microbial functioning in a bioreactor treating wastewater. We investigated the effect of incremental concentrations of Cu, Zn and Ni on the bacterial community structure and their metabolic functions by shotgun metagenomics. Metal concentrations reported in previous studies to inhibit bacterial metabolism were investigated.

RESULTS

At 31.5 μM Cu, 112.4 μM Ni and 122.3 μM Zn, the most abundant bacteria were Achromobacter and Agrobacterium. When the metal concentration increased 2 or fivefold their abundance decreased and members of Delftia, Stenotrophomonas and Sphingomonas dominated. Although the heterotrophic metabolic functions based on the gene profile was not affected when the metal concentration increased, changes in the sulfur biogeochemical cycle were detected. Despite the large variations in the bacterial community structure when concentrations of Cu, Zn and Ni increased in the bioreactor, functional changes in carbon metabolism were small.

CONCLUSIONS

Community richness and diversity replacement indexes decreased significantly with increased metal concentration. Delftia antagonized Pseudomonas and members of Xanthomonadaceae. The relative abundance of most bacterial genes remained unchanged despite a five-fold increase in the metal concentration, but that of some EPS genes required for exopolysaccharide synthesis, and those related to the reduction of nitrite to nitrous oxide decreased which may alter the bioreactor functioning.