Influence of cadmium and copper mixtures to rhizosphere bacterial communities

To study the effects of combined Cd and Cu pollution on rhizosphere bacterial community. High-throughput sequencing was used to examine the response of rhizosphere bacterial communities to heavy-metal stress under single and mixed pollution of cadmium (Cd) and copper (Cu). With additions of Cd and Cu, the mean diversity index of rhizosphere bacterial community was in the order Cu alone > Cd-Cu mixtures > Cd alone. In all Cd and Cu treatments, the dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria. In the additions with different concentrations of Cd-Cu mixtures, LEfSe indicated that there were differences in the predominant species of rhizosphere bacterial communities. Some genera such as Streptomyces and Microbacterium belonging to Actinobacteria as biomarkers were significantly enriched in both control and treatments, while some genera such as Pseudoxanthomonas and Rhodopseudomonas belonging to Proteobacteria as biomarkers were observed to be enriched in the additions with single and mixture of Cd and Cu. According to the Nonmetric multidimensional scaling (NMDS) analysis, the structure of rhizosphere bacterial community was different between treatments and the CK. Principal Component Analysis (PCA) and permutational multivariate analysis of variance (PERMANOVA) showed that there were significant differences among treatments (p < 0.01), and that the addition of Cu might be the primary factor affecting the composition of rhizosphere bacterial communities.