In the present study, the microbial diversity in anaerobic reactors, continuously exposed to oleate, added to a manure reactor influent, was investigated. Relative changes in archaeal community were less remarkable in comparison to changes in bacterial community indicating that dominant archaeal composition remained relatively stable. Majority of the analyzed bacterial amplicons were phylogenetically affiliated with uncultured bacteria belonging to Firmicutes, Bacteroidetes, Proteobacteria and Thermotogae phyla. Bacterial community changes in response to oleate addition resulted in a less diverse bacterial consortium related to functional specialization of the species towards oleate degradation. For the archaeal domain, the sequences were affiliated within Euryarchaeota phylum with three major groups (Methanosarcina, Methanosaeta and Methanobacterium genera). Results obtained in this study deliver a comprehensive picture on oleate degrading microbial communities in high organic strength wastewater. The findings might be utilized for development of strategies for biogas production from lipid-riched wastes. (C) 2011 Elsevier Ltd. All rights reserved.