Effect of Elodea nuttallii roots on bacterial communities and MMHg proportion in a Hg polluted sediment

• Published in: PloS one Vol. 7; no. 9; p. e45565
• Main Authors: Regier, Nicole, Frey, Beat, Converse, Brandon, Roden, Eric, Grosse-Honebrink, Alexander, Bravo, Andrea Garcia, Cosio, Claudia
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 17-09-2012; Public Library of Science (PLoS)
• Subjects: Aquatic plants; Bacteria; Bacteria - classification; Bacteria - genetics; Biogeochemistry; Biology; Cloning; Communities; Community structure; Comparative analysis; Contaminated sediments; Contamination; Earth science; Earth Sciences; Ecosystems; Ecotoxicology; Elodea nuttallii; Environmental aspects; Environmental Pollution; Environmental science; Genes; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Hydrocharitaceae - physiology; Life Sciences; Macrophytes; Mercury; Mercury (Metal); Mercury - chemistry; Methylation; Methylmercury Compounds - chemistry; Phylogenetics; Phylogeny; Plant Roots - physiology; Pore water; Principal components analysis; Rhizosphere; Rivers; Rivers - chemistry; Rivers - microbiology; RNA, Ribosomal, 16S; Roots; Sediment pollution; Sediments; Sediments (Geology); Soil microbiology; Studies; Sulfate-reducing bacteria; Sulfates; Toxicology; Water pollution; Water Pollution, Chemical; United States; Switzerland; United States > US; Wisconsin
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0045565

The objective of this study was to assess the effect of a rooted macrophyte Elodea nuttallii on rhizosphere bacterial communities in Hg contaminated sediments. Specimens of E. nuttallii were exposed to sediments from the Hg contaminated Babeni reservoir (Olt River, Romania) in our microcosm. Plants were allowed to grow for two months until they occupied the entirety of the sediments. Total Hg and MMHg were analysed in sediments where an increased MMHg percentage of the total Hg in pore water of rhizosphere sediments was found. E. nuttallii roots also significantly changed the bacterial community structure in rhizosphere sediments compared to bulk sediments. Deltaproteobacteria dominated the rhizosphere bacterial community where members of Geobacteraceae within the Desulfuromonadales and Desulfobacteraceae were identified. Two bacterial operational taxonomic units (OTUs) which were phylogenetically related to sulfate-reducing bacteria (SRB) became abundant in the rhizosphere. We suggest that these phylotypes could be potentially methylating bacteria and might be responsible for the higher MMHg percentage of the total Hg in rhizosphere sediments. However, SRB were not significantly favoured in rhizosphere sediments as shown by qPCR. Our findings support the hypothesis that rooted macrophytes created a microenvironment favorable for Hg methylation. The presence of E. nuttallii in Hg contaminated sediments should therefore not be overlooked.