Page 161 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Bacterial and archaeal community composition in the lake sediments
One of the duplicate cores taken per sample site was used for further studies. For each core, the 16S rRNA genes were amplified using two distinct primer sets targeting Bacteria and Archaea and were sequenced with Illumina technology. The total abundance of Bacteria and Archaea was quantified by qPCR and showed that Bacteria were seven times more abundant based on copy number than the Archaea in all sediment cores (Fig. 1). The bacterial community structure was similar in both lakes, which was supported by non-metric multidimensional scaling (NMDS) analysis (Supplemental Figure S2 and S3). Diversity analysis using the Simpson and Shannon diversity indices indicate similar diversity for the seven thermokarst lake sediment cores with higher diversity for the bacterial than the archaeal community on OTU level (Supplemental Tables S4 and S5). This was also reflected by the Chao1 species richness estimation (Supplemental Tables S4 and S5). Additionally, both Simpson- and Shannon-based evenness were similar in all cores for both the archaeal and bacterial communities (Supplemental Tables S4 and S5). The bacterial community was very diverse (Fig. 1): a rare microbial biosphere prevailed with around 50% of the reads affiliated to groups with an individual relative abundance of less than 2%. The most abundant bacteria belonged to Bacteriodetes with 16-19%, followed by 9-17% assigned to Nitrosomonadales, and 4-8% of the Anaerolineales order. A difference between the lakes was observed in the abundance of Campylobacterales (Epsilonproteobacteria) in Lake Emaiksoun (3-8%) compared to <2% in Unnamed Lake. Most archaeal reads (16-40%) in Lake Emaiksoun were affiliated to Rice Cluster II organisms, whereas Methanosaetaceae (30-31%) reads showed highest relative abundance in Unnamed Lake (Fig. 1). The second most abundant phylum was Bathyarchaeota (17-24% in Lake Emaiksoun, and 27-28% in Unnamed Lake). Woesearchaeota were present in both lakes (8-10% in Emaiksoun Lake; 5-8% in Unnamed Lake).
7
159