fused to a portion of the diagnostic gene for dissimilatory sulfite reduction (dsrB)
to probe for functional information. Cells were trapped in 10-μm-diameter
polyacrylamide beads50. Poisson statistics predict that only 0.45% of beads will
contain more than one cell. The DNA trapped within the beads was used as the
template for PCR inside an emulsion51. The first set of primers for 16S rRNA gene
amplification include U515F and 1492R and the fusion reaction was nested within the
16S gene using E786R. The dsrB gene primers were adapted fromWagner et al.52 and
slightly modified to fit the needs of the molecular construct. Sequences and the results
of a traditional dsrB survey are provided in the original publication. The dsrB gene is
highly conserved across known sulfate reducers53, but it is possible that there are
variants of the gene that are prevalent in the lake that these primers did not amplify,
in which case the following analysis would contain false negatives (that is, OTUs that
can reduce sulfate but did not produce 16S-dsrB amplicons). Comparison of the
dsrB-16S rRNA gene fusion assay to a bulk dsrB gene survey in the original
previous analysis demonstrates significant overlap26, showing the fusion PCR
assay targets a wide variety of reductive dsrB genes from the Deltaproteobacteria
dsrB supercluster.
Accession codes. All clone sequences have been submitted to GenBank (accession
nos. KC192376 to KC192544). Illumina data have been submitted to the Sequence
Read Archive under study accession no. PRJNA217938.
Received 5 October 2015; accepted 30 June 2016;
published 15 August 2016