Long chain fatty acids (LCFA) are frequently found in wastewaters as the main product of lipid
hydrolysis. These compounds hold a high energetic potential and thus are attractive substrates for
methane production. Insight into the microbial populations involved in anaerobic LCFA-degradation is
important for the development and improvement of technologies for lipids/LCFA-rich wastewater
valorisation.
This study identifies putative LCFA-degrading bacteria by combining selective enrichments with
molecular techniques. Two distinct enrichment series of anaerobic cultures growing on unsaturatedand
saturated-LCFA were obtained by successive transfers in medium containing oleate (C18:1) and
palmitate (C16:0), respectively, as the sole carbon and energy source. This procedure resulted in two
stable and highly enriched cultures that could convert oleate and palmitate to acetate and methane.
Changes in the microbial composition during the enrichment were analyzed by 16S rRNA gene PCRDGGE
profiling. Upon enrichment a decrease in microbial diversity was observed. Prominent bands in
the DGGE profiles of stable enriched cultures were identified by 16S rRNA gene sequencing, and
nearly full sequences were compared using ARB software. A major part of the retrieved 16S rRNA
gene sequences was most similar to those of uncultured bacteria. Organisms corresponding to
dominant DGGE bands in oleate- and palmitate-enrichment cultures clustered with fatty-acid
oxidizing syntrophic bacteria within Syntrophomonadaceae and Syntrophaceae families. Despite the
absence of sulphate in the medium, a Desulfovibrio-like organism was detected as a dominant band in
the DGGE profile of the oleate-enrichment culture. In other studies Desulfovibrio species have been
detected in methanogenic reactors without added sulphate. They were proposed to grow
acetogenically. The role of such bacteria in the oleate-enrichment culture is not clear yet, and this
needs further investigation. A low methane yield (12%) was observed in the oleate-enrichment and
acetate, produced according to the expected stoichiometry, was no further converted to methane. In the
palmitate-enrichment culture, the acetate produced was completely mineralised and a total methane
yield of about 83% was achieved from palmitate degradation. Furthermore, the oleate-enrichment
culture was able to use palmitate without detectable changes in the DGGE profile. However, the
palmitate-specialised consortia degraded oleate only after a lag phase of three months, after which the
DGGE profile was changed. A dominant band appeared and sequence analysis showed affiliation with
the Syntrophomonas genus. This band was also present in the oleate-enrichment culture, suggesting
that this bacterium is important for oleate degradation, emphasizing possible differences between the
degradation of unsaturated- and saturated-LCFA
