Fig. 1

Microbial composition in the obtained enrichment cultures. a Maximum likelihood phylogenetic tree of full-length 16S rRNA gene sequences of Desulfobulbaceae retrieved from the NCBI database in comparison to the cable bacteria (MAG Dsb_1MN) from culture 1MN (red frame). Partial sequences from amplicon sequencing (OTU 1) and sequences from the metagenomes of culture 1MN (MAG Dsb_1MN) and the cable bacteria enrichment showed 100% similarity. Scale bar represents the number of substitutions per site. Known cable bacteria are represented by full-length 16S gene sequences of Candidatus Electrothrix and Candidatus Electronema. b Changes in microbial community composition of culture 1MN in the presence of different electron donor and acceptor combinations. The relative abundances of the MAG Dsb_1MN population and the Thermoanaerobacteraceae in the culture grown on 1-methylnaphthalene and ferrihydrite (top panel) were deduced from the average read coverage in the metagenome, which confirmed previous results obtained from fingerprinting by T-RFLP (14). The relative abundances in the absence of 1-methylnaphthalene were inferred from fingerprinting by T-RFLP and confirmed by amplicon sequencing (Fig. S6). c Fluorescence in situ hybridization (FISH) of the cable bacteria enrichment culture grown with elemental sulfur as electron donor and nitrate as electron acceptor stained with probe FliDSB194 specific for the MAG Dsb_1MN cable bacteria population. d Atomic force micrograph of filaments in culture 1MN grown with elemental sulfur and nitrate as electron acceptor showing the characteristic cell envelope of cable bacteria. The image displays the vertical deflection measured in contact mode