Hydrogen production potential of fermentative microorganisms from the Sargasso Sea

Mounting evidence suggests that ammonia-oxidizing archaea (AOA) may play important roles in nitrogen cycling in geothermal environments. In this study, the diversity, distribution and ecological significance of AOA in terrestrial hot springs in Kamchatka (Far East Russia) were explored using amoA genes complemented by analysis of glycerol dialkyl glycerol tetraethers (GDGTs) of archaea. PCR amplification of functional genes (amoA) from AOA and ammonia-oxidizing bacteria (AOB) was performed on microbial mats/streamers and sediments collected from three hot springs (42°C to 87°C and pH 5.5-7.0). No amoA genes of AOB were detected. The amoA genes of AOA formed three distinct phylogenetic clusters with Cluster 3 representing the majority (～59%) of OTUs. Some of the sequences from Cluster 3 were closely related to those from acidic soil environments, which is consistent with the predominance of low pH (<7.0) in these hot springs. Species richness (estimated by Chao1) was more frequently higher at temperatures below 75°C than above it, indicating that AOA may be favored in the moderately high temperature environments. Quantitative PCR of 16S rRNA genes showed that crenarchaeota counted for up to 80% of total archaea. S-LIBSHUFF separated all samples into two phylogenetic groups. The profiles of GDGTs were well separated among the studied springs, suggesting a spatial patterning of archaeal lipid biomarkers. However, this patterning did not correlate significantly with variation in archaeal amoA, suggesting that AOA are not the predominant archaeal group in these springs producing the observed GDGTs.