Methanogenic diversity and activity in municipal solid waste landfill leachates

Landfilling still represent the most common way to handle the ever-increasing amount of Municipal Solid Waste (MSW). Methanogenesis is largely responsible of the environmental benefits (biogas valorisation) or burdens (unwanted emissions, slow stabilization, ) associated with landfilling. This key function is catalysed by a limited number of monophyletic groups of archaea, each having their own metabolic characteristics. Functional information may thus be inferred from phylogenetic studies on methanogens. We therefore conducted a 16S rRNA survey of archaeal populations in different landfill leachates samples and determined 239 partial length sequences. 65% of the sequenced clones were closely related to the strictly acetoclastic methanogenic family Methanosaetaceae, 18% to the metabolically versatile family Methanosarcinaceae and 10% to members of the hydrogenotrophic order Methanomicrobiales. Eleven euryarchaeal and thirteen crenarchaeal sequences only (i.e. 10 %) were distantly related to any hitherto cultivated microorganisms, showing a limited archaeal diversity. Labscale incubations were thereafter performed with leachates mixed with several methanogenic precursors (acetate, hydrogen, formate, methanol, methylamine). Microbial populations were followed by FISH using group specific probes. Aceticlastic methanogenesis was rapidly induced and led to the dominance of members of the family Methanosarcinaceae (probe MS1414). Hydrogen, formate, methanol and methylamine addition induced an important acetate synthesis resulting from the onset of a homoacetogenic metabolism. In these incubations, species belonging to the family Methanosarcinaceae (probe MS1414) and the order Methanomicrobiales (probe EURY496) were dominant. These observations confirm that aceticlastic methanogenesis performed by the members of the order Methanosarcinales is predominant over the hydrogenotrophic and methylotrophic pathways in landfill leachates. / Présentation par poster au colloque ISME-11 International Symposium on Microbial Ecology, 20-25 August 2006, Vienna, AUSTRIA.