FIGURE 4.

Sequence composition-independent binning of the metagenome scaffolds from two ammonia-oxidizing enrichment cultures. Circles represent scaffolds, scaled by the square root of their length. Clusters of similarly colored circles represent potential genome bins. The x-axis shows binning of the scaffolds from an early enrichment culture, which still included other genera as well (not shown). The y-axis shows binning of the scaffolds from the latest enrichment culture containing only “Ca. N. islandicus” and the two remaining accompanying organisms. Genome bins for the Thermus (34% complete) and the Chloroflexi (56% complete) organism were obtained. The genome bin of the Chloroflexi organism contains genes that cluster within a clade of Nitrobacter/Nitrolancea nitrite oxidoreductase (nxrAB) genes (data not shown). Some nitrate production by the batch enrichment culture was observed after multiple re-feedings with NH₄⁺ (>20 mM). As NOB in the phylum Chloroflexi are known (Sorokin et al., 2012), it is tempting to speculate that this Chloroflexi may be a thermophilic nitrite oxidizer.