Investigation of the ecological roles of the plastisphere microbiome in metal-contaminated river sediments: elucidation of their metabolic versatilities for plastics mineralization and metal resistance

Abstract

Both plastics and heavy metal(loid)s (HMs) are ubiquitous environmental contaminants, and their frequent interactions in aquatic environments are observed globally. These interactions could result in adsorption of HMs onto plastics, thereby altering the environmental behavior of both contaminants. The change of physicochemical property of plastics surfaces, due to HM adsorption, inevitably impacts the plastisphere microbiome, as well as the fate of plastics in the environment. However, our understanding of how plastisphere microbiomes respond to HMs stress, and the subsequent impacts on the fate of plastics and HMs, remain in its infancy. The current study identified keystone taxa of the plastisphere microbiome and identified their ecological roles in HM metabolism. Members of Mycobacterium were identified as the keystone taxa in the HM contaminated plastisphere. Metagenomic binning and pangenome analysis demonstrated that Mycobacterium encoded essential genes for plastics biodegradation and HM resistance. Pure isolates of Mycobacterium further confirmed that the bacteria can mineralize plastics under arsenic exposure, with plastics biodegradation rates remaining unaffected by environmentally relevant As concentrations (up to 0.5 mM). In summary, the metabolic potentials of HM detoxification as well as the mineralization of plastics by the keystone taxa of the plastisphere microbiome may play important environmental service to promote the bioremediation of the co-contamination of HMs and plastics.