title: Multi-year and short-term responses of soil ammonia-oxidizing prokaryotes to zinc bacitracin, monensin, and ivermectin, singly or in combination.
abstract: A field experiment was initiated whereby a series of replicated plots received annual applications of ivermectin, monensin, and zinc bacitracin, either singly or in a mixture. Pharmaceuticals were added at concentrations of 0.1 mg/kg soil or 10 mg/kg soil. The authors collected soil samples in 2013, before and after the fourth annual application of pharmaceuticals. In addition, a 30-d laboratory experiment was undertaken with the same soil and same pharmaceuticals, but at concentrations of 100 mg/kg soil. The impact of the pharmaceuticals on nitrification rates, on the abundance of ammonia-oxidizing bacteria (AOB), and on the abundance of ammonia-oxidizing archaea (AOA) was assessed. None of the pharmaceuticals at 0.1 mg/kg had any effect on nitrification. Referenced to control soil, nitrification was accelerated in soil exposed to 100 mg/kg zinc bacitracin or 10 mg/kg of the pharmaceutical mixture, but none of the treatments inhibited nitrification. Neither AOB abundance nor AOA abundance was affected by the pharmaceuticals at 0.1 mg/kg. At 10 mg/kg, monensin, zinc bacitracin, and a mixture of all 3 pharmaceuticals suppressed the abundance of AOB, and zinc bacitracin and the mixture increased AOA abundance. The decrease in AOB abundance and increase in AOA abundance when exposed to 10 mg/kg soil suggests that AOB are more sensitive to these chemicals and that AOA populations can expand to occupy the partially vacated niche.
authors.affiliation: Department of Biology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Konopka
authors.initials: K
authors.lastname: Magda
authors.forename: Henry
authors.initials: H
authors.lastname: Hugh A L
authors.forename: Marti
authors.initials: M
authors.lastname: Romain
authors.forename: Topp
authors.initials: T
authors.lastname: Edward
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D001105:Archaea / Q000187:drug effects / Q000378:metabolism*; D001414:Bacitracin / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects / Q000378:metabolism*; D007559:Ivermectin / Q000494:pharmacology*; D008985:Monensin / Q000494:pharmacology*; D058465:Nitrification / Q000187:drug effects; D010084:Oxidation-Reduction / Q000187:drug effects; D011387:Prokaryotic Cells / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D013997:Time Factors
chemical_list: D012335:RNA, Ribosomal; D012987:Soil; D001414:Bacitracin; D007559:Ivermectin; D000641:Ammonia; D008985:Monensin
keywords: Agriculture; Ammonia oxidizers; Nitrification; Pharmaceuticals; Soil