Figure 5
Organization (a), phylogeny (b) and distribution (c and d) of genes coding for nitrite oxidoreductase (NXR) in the Red Sea SAGs. (a) Shows the NXR gene cluster (in bold) in one of the RS-SAGs (SCGC AAA799-C22), whereas (b) illustrates the phylogenetic position of the nxrA genes among other selected members of the type II dimethyl sulphoxide reductase enzyme family. Coloured leaves of the maximum-likelihood tree show the placement of the two distinct forms of nxrA genes of low- and high-affinity NOB discussed in the main text. Validated aerobic nitrite oxidizers are marked with an asterisk, whereas Ca. Nitromaritima SAGs are shown in bold. (c and d) The frequency of key genes for nitrite dissimilation (relative to housekeeping genes) and the taxonomy of nxrA genes in metagenomic data sets, whereas (e) highlights the variability in three key environmental variables among these data sets. ‘Anammox-like’ refers to anaerobic ammonia-oxidizing Planctomycetes. Note that the frequency of nxrA gene types of anammox bacteria is combined together with those of high-affinity NOB in panel c.
