| dc.description.abstract | Wastewater treatment plants often use methanol to drive denitrification for nitrogen removal. This can lead to excess methanol reaching water bodies through the effluent discharge. This excess methanol can stimulate methylotrophic methanogenesis in marine sediments, potentially increasing methane production.The current thesis investigated the enrichment of microorganisms capable of methylotrophic methanogenesis in sediment samples from the Oslo fjord. Microcosms consisting of sediment material and synthetic seawater were enriched in four different ways. Enrichments were performed using methanol, nitrate and methanol and nitrate together as well as a control. The microcosms were monitored over time by measuring NO3-, NO2-, NH3/NH4+, pH and ORP every 2-3 days. Sediment samples were collected every 3-4 days and DNA was extracted. The extracted DNA was analysed using qPCR, 16S rRNA amplicon sequencing and shotgun metagenomic sequencing to investigate the inferred taxonomic composition and the genetic potential of the methylotrophic methanogens in the sediments.The results revealed a significant enrichment of methanogenic archaea within the family Methanosarcinaceae for samples amended with methanol after 17 and 21 days of incubation at ORPs higher than +50 mV. This was both observed using relative read counts from 16S rRNA amplicon analysis, as well as FAPROTAX analysis that inferred metabolic processes to the taxa identified from the 16S rRNA sequences.Investigation of the shotgun sequencing data revealed three MAGs that were taxonomically annotated as archaea belonging to the family Methanosarcinaceae. The genomic potential in each of these MAGs were investigated for presence of methanogenesis genes, and for completeness of the relevant pathways. Methyl reduction was revealed as the most probable methylotrophic pathway. The number of genes in each MAG that were related to methanogenesis from methanol varied, but all MAGs contained the genes mcrABG, mtaB and mtaC which convert methanol into methyl-CoM and further into methane. MtaA was identified in two of the three MAGs.The enrichment of Methanosarcinaceae occurred at higher ORP measurements than expected from literature. This is an interesting aspect of the results, that should be followed up in future research based on methylotrophic methanogenesis in marine sediments. | |
