Nitrate-reducing bacterial community in a biofilm-electrode reactor

Bacterial community structure corresponds to performance during cathodic nitrate reduction

“…The enrichment of Gammaproteobacteria, Betaproteobacteria and Firmicutes has been detected in previous studies characterizing denitrification from waste treatment systems (Knowles, 1982). More significantly, the dominance of the Proteobacteria in five of the six non-loop reactors is consistent with identification in the two previously reported nonloop denitrifying biocathode studies (Park et al, 2006;. Although 16S rRNA does not indicate physiological function, the congruence between multiple community data sets from different inoculum, sampling regimes and reactor designs suggests a functional role for members of the Gammaproteobacteria and Betaproteobacteria in cathodic denitrifying biofilms.…”

“…Although we restricted our analysis to only the most active community members (16S rRNA) and previous studies relied on persistent and active members (16S rRNA gene), the use of the PhyloChip uncovered significantly greater numbers of OTUs than was reported in previous BES studies. In comparison to the richness described here (Figure 6, x axis), only four dominant DGGE bands (Park et al, 2006) or two dominant genera (Gregory and et al, 2004) were identified in other studies. Reasons for this discrepancy probably have less to do with vast differences in community richness associated with our reactors, but are more likely attributed to the limitation of the technique (DGGE) or small sampling regimes (o90 clones) that failed to capture a large fraction of the biofilm bacterial diversity.…”

“…Noted that Gram-positive bacteria were enriched in denitrifying biocathode communities and were not-detected in control cathodes without current. Sequences similar to Bacillus vedderi were identified as dominant member of biocathode communities by Park et al (2006), whereas Gregory et al (2004) noted that Gram-positive bacteria were enriched in denitrifying biocathode communities and not in no-current controls; unfortunately taxonomic identification of these bacteria was not provided.…”

“…With the exception of ANL_T2, our non-loop reactors samples were enriched in members of the order Burkholderiales of the Betaproteobacteria (10 of 14 taxa, 71%). Park et al (2006) also identified a member of the Burkholderiales as dominant in denitrifying cathodes. The former study used 16S rRNA gene analysis with denaturing gradient gel electrophoresis (DGGE) and FISH to speculate that members from the family Burkholderiaceae most closely related (97%) to a Burkholderia symbiont of Asellus aquaticus were abundant in denitrifying biofilms.…”

“…Our current knowledge of bacterial denitrification reactions relevant to BES cathodes is based on pure-culture studies of chemolithotrophic denitrification coupled to inorganic electron donors (Fernández et al, 2008;Weber et al, 2006) and cathodes as electron donors for anaerobic respiration (Gregory et al, 2004;Thrash et al, 2007;Strycharz et al, 2008;Thrash and Coates, 2008;He et al, 2009). Presently, only two studies examined microbial biofilm communities in denitrifying BESs (Gregory et al, 2004;Park et al, 2006).…”