title: Responses of mixed methanotrophic consortia to variable Cu2+/Fe2+ratios.
abstract: Methane mitigation in landfill top cover soils is mediated by methanotrophs whose optimal methane (CH4) oxidation capacity is governed by environmental and complex microbial community interactions. Optimization of CH4remediating bio-filters need to take microbial responses into account. Divalent copper (Cu2+) and iron (Fe2+) are present in landfills at variable ratios and play a vital role in methane oxidation capacity and growth of methanotrophs. This study, as a first of its kind, therefore quantified effects of variable Cu2+and Fe2+(5:5, 5:25 and 5:50 μM) ratios on mixed methanotrophic communities enriched from landfill top cover (LB) and compost soils (CB). CH4oxidation capacity, CH4removal efficiencies, fatty acids content/profiles and polyhydroxybutyrate (PHB; a biopolymer) contents were also analysed to quantify performance and potential co-product development. Mixed methanotroph cultures were raised in 10 L continuous stirred tank reactors (CSTRs, Bioflo®& Celligen®310 Fermentor/Bioreactor; John Morris Scientific, Chatswood, NSW, Australia). Community structure was determined by amplifying the V3-V4 region of 16s rRNA gene. Community structure and, consequently, fatty acid-profiles changed significantly with increasing Cu2+/Fe2+ratios, and responses were different for LB and CB. Effects on methane oxidation capacities and PHB content were similar in the LB- and CB-CSTR, decreasing with increasing Cu2+/Fe2+ratios, while biomass growth was unaffected. In general, high Fe2+concentration favored growth of the type -II methanotroph Methylosinus in the CB-CSTR, but methanotroph abundances decreased in the LB-CSTR. Increase in Cu2+/Fe2+ratio increased the growth of Sphingopyxis in both systems, while Azospirllum was co-dominant in the LB- but absent in the CB-CSTR. After 13 days, methane oxidation capacities and PHB content decreased by ∼50% and more in response to increasing Fe2+concentrations. Although methanotroph abundance was ∼2% in the LB- (compared to >50% in CB-CSTR), methane oxidation capacities were comparable in the two systems, suggesting that methane oxidation capacity was maintained by the dominant Azospirllum and Sphingopyxis in the LB-CSTR. Despite similar methanotroph inoculum community composition and controlled environmental variables, increasing Cu2+/Fe2+ratios resulted in significantly different microbial community structures in the LB- and CB-CSTR, indicative of complex microbial interactions. In summary, our results suggest that a detailed understanding of allelopathic interactions in mixed methanotrophic consortia is vital for constructing robust bio-filters for CH4emission abatement.
authors.affiliation: College of Science and Engineering, James Cook University, Townsville 4811, Queensland, Australia; Centre for Sustainable Tropical Fisheries and Aquaculture, James Cook University, Townsville 4811, Queensland, Australia.
authors.forename: Karthigeyan
authors.initials: K
authors.lastname: Chidambarampadmavathy
authors.affiliation: College of Science and Engineering, James Cook University, Townsville 4811, Queensland, Australia; Comparative Genomics Centre, James Cook University, Townsville 4811, Queensland, Australia; Centre for Sustainable Tropical Fisheries and Aquaculture, James Cook University, Townsville 4811, Queensland, Australia; Sino-Forest Applied Research Centre for Pearl River Delta Environment (ARCPE), Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China.
authors.forename: Obulisamy Parthiba
authors.initials: OP
authors.lastname: Karthikeyan
authors.affiliation: College of Science and Engineering, James Cook University, Townsville 4811, Queensland, Australia; Comparative Genomics Centre, James Cook University, Townsville 4811, Queensland, Australia; Centre for Sustainable Tropical Fisheries and Aquaculture, James Cook University, Townsville 4811, Queensland, Australia.
authors.forename: Roger
authors.initials: R
authors.lastname: Huerlimann
authors.affiliation: College of Science and Engineering, James Cook University, Townsville 4811, Queensland, Australia; Comparative Genomics Centre, James Cook University, Townsville 4811, Queensland, Australia; Centre for Sustainable Tropical Fisheries and Aquaculture, James Cook University, Townsville 4811, Queensland, Australia.
authors.forename: Gregory E
authors.initials: GE
authors.lastname: Maes
authors.affiliation: College of Science and Engineering, James Cook University, Townsville 4811, Queensland, Australia; Comparative Genomics Centre, James Cook University, Townsville 4811, Queensland, Australia; Centre for Sustainable Tropical Fisheries and Aquaculture, James Cook University, Townsville 4811, Queensland, Australia; Centre for Bio-discovery and Molecular Development of Therapeutics, James Cook University, Townsville 4811, Queensland, Australia. Electronic address: kirsten.heimann@jcu.edu.au.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Heimann
mesh_terms: D001315:Australia; D008697:Methane; D010084:Oxidation-Reduction; D012336:RNA, Ribosomal, 16S; D012988:Soil Microbiology; D064091:Waste Disposal Facilities
chemical_list: D012336:RNA, Ribosomal, 16S; D008697:Methane
keywords: Biopolymers; Bioreactor; Heavy metal; Methane; Methanotrophs; Microbial community