Impacts of single-walled carbon nanotubes on microbial community structure in activated sludge

Aims: Single-walled carbon nanotubes (SWNTs) are likely to become increasingly widespread and yet their environmental impact is not well understood. The purpose of the current study was to evaluate the impact of SWNTs on microbial communities in a 'sentinel' environmental system, activated sludge batch-scale reactors. Methods and Results: Triplicate batch reactors were exposed to SWNTs and compared to control reactors exposed to impurities associated with SWNTs. Automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterial community structure in each reactor. SWNT exposure was found to impact microbial community structure, while SWNT-associated impurities had no effect, compared to controls. 16S rRNA gene sequence analysis indicated that dominant phylotypes detected by ARISA included members of the families Sphingomonadaceae and Cytophagacaceae and the genus Zoogloea. ARISA results indicated an adverse impact of SWNTs on the sphingomonad relative to other community members. Changes in community structure also occurred in both SWNT-exposed and control reactors over the experimental time period and with the date on which activated sludge was obtained from a wastewater treatment facility. Conclusions: These results indicate that SWNTs differentially impact members of the activated sludge reactor bacterial community. Significance and Impact of the Study: The finding that community structure was affected by SWNTs indicates that this emerging contaminant differentially impacted members of the activated sludge bacterial community and raises the concern that SWNTs may also affect the services it provides.