| Summary: | Verkefnið er opið nemendum og starfsfólki Háskólans á Akureyri frá og með 23.maí 2009. Twenty seven thermophilic hydrogen oxidizing cultures (pure cultures or co-cultures) were obtained from various hot springs in Grensdalur, Hveragerði in SW-Iceland. The cultures were investigated in detail with respect to phylogenetics, physiology, hydrogen uptake rates and biomass yield. Enrichments under hydrogen oxidation conditions showed that 10% oxygen gave best results for obtaining stable pure- or co-cultures. Phylogenetic studies of the enrichments were done with partial- and full 16S rRNA analysis and DGGE analysis. Four main groups of hydrogen oxidizing bacteria were detected in the enrichment cultures obtained. The closest similarities were to species within the genera of Hydrogenophilus, Thiomonas (moderate thermophiles), Hydrogenobacter and Sulfurihydrogenibium (true thermophiles). Three enrichments revealed bacteria close to Hydrogenophilus denitrificans and H. thermoluteolus. Three enrichments resulted in bacteria closely related to several species of Thiomonas. Fourteen enrichments gave closest relationship to strict chemolithotrophs belonging to Hydrogenobacter and five enrichments showed the closest relationship to Sulfurihydrogenibium sp. Phylogenetic studies also showed that heterotrophic bacteria were very persistent. Among contaminants were Meiothermus, Anoxybacillus and Geobbacillus sp. Batch experiments on all enrichments showed great variation in hydrogen oxidation rate and biomass yield. The hydrogen oxidation rate varied from 0,16 to 1,64 mol H2L-1h-1 and the biomass yield from 0,21 – 3,18 g DCW per mol H2 consumed. In general, the moderate thermophilic enrichments oxidized hydrogen faster as compared with the true thermophiles and produced more biomass. Cultivation in fed batch cultures of selected enrichments resulted in higher hydrogen uptake rates and biomass formation compared with batch cultures. The maximum hydrogen uptake rate and biomass yield for Ralstonia eutropha was 15,05 H2L-1h-1 and ...
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