Response of Microbial Community Function to Fluctuating Geochemical Conditions within a Legacy Radioactive Waste Trench Environment

• Published in: Applied and environmental microbiology Vol. 83; no. 17
• Main Authors: Vázquez-Campos, Xabier, Kinsela, Andrew S, Bligh, Mark W, Harrison, Jennifer J, Payne, Timothy E, Waite, T David
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01-09-2017
• Subjects: Aerobes; Americium; Anaerobes; Associated species; Australia; Bacteria - classification; Bacteria - genetics; Bacteria - isolation & purification; Bacteria - metabolism; Communities; Contaminants; Ecological effects; Ecological monitoring; Environment; Genomics; Geochemistry; Geologic Sediments - analysis; Geologic Sediments - microbiology; Geomicrobiology; Groundwater - microbiology; Iron; Metagenomics; Methanogenesis; Microbiomes; Microorganisms; Phylogeny; Plutonium; Radioactive materials; Radioactive Waste - analysis; Radioactive wastes; Radiochemistry; Rain water; Rainfall; Redox properties; Sampling; Sulfate reduction; Trenches; Water levels; Water Microbiology; Sydney New South Wales Australia; Australia; shotgun metagenomics; radionuclides; americium; functional profile; plutonium
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.00729-17

During the 1960s, small quantities of radioactive materials were codisposed with chemical waste at the Little Forest Legacy Site (Sydney, Australia) in 3-meter-deep, unlined trenches. Chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a 6-week period immediately after a prolonged rainfall event to assess the impact of changing water levels upon the microbial ecology and contaminant mobility. Collectively, results demonstrated that oxygen-laden rainwater rapidly altered the redox balance in the trench water, strongly impacting microbial functioning as well as the radiochemistry. Two contaminants of concern, plutonium and americium, were shown to transition from solid-iron-associated species immediately after the initial rainwater pulse to progressively more soluble moieties as reducing conditions were enhanced. Functional metagenomics revealed the potentially important role that the taxonomically diverse microbial community played in this transition. In particular, aerobes dominated in the first day, followed by an increase of facultative anaerobes/denitrifiers at day 4. Toward the mid-end of the sampling period, the functional and taxonomic profiles depicted an anaerobic community distinguished by a higher representation of dissimilatory sulfate reduction and methanogenesis pathways. Our results have important implications to similar near-surface environmental systems in which redox cycling occurs.
The role of chemical and microbiological factors in mediating the biogeochemistry of groundwaters from trenches used to dispose of radioactive materials during the 1960s is examined in this study. Specifically, chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a 6-week period immediately after a prolonged rainfall event to assess how changing water levels influence microbial ecology and contaminant mobility. Results demonstrate that oxygen-laden rainwater rapidly altered the redox balance in the trench water, strongly impacting microbial functioning as well as the radiochemistry. Two contaminants of concern, plutonium and americium, were shown to transition from solid-iron-associated species immediately after the initial rainwater pulse to progressively more soluble moieties as reducing conditions were enhanced. Functional metagenomics revealed the important role that the taxonomically diverse microbial community played in this transition. Our results have important implications to similar near-surface environmental systems in which redox cycling occurs.