To probe the genetic capability of OTUs to perform sulfate
reduction, we targeted a gene, the dissimilatory sulfite reductase
gene (dsrB), the product of which is a key enzyme in sulfate
reduction25. Specifically, we used a single-cell gene-fusion
technique26 that amplifies the 16S rRNA gene only in organisms
whose genomes contain dsrB. The technique traps cells in polyacrylamide
beads during DNA extraction, isolates the extraction
products in oil droplets and amplifies a concatenation of the dsrB
and 16S sequences using within-droplet PCR. As a control, we
performed a non-specific fusion assay to verify that a wide range
of taxonomic marker sequences can be amplified with this
method (Fig. 5).
The single-cell assay amplified 16S-dsrB amplicons whose 16S
rRNA gene sequences corresponded to a small number of OTUs.
Only four OTUs that appear in any of the OEUs were amplified