Abstract
The betaproteobacterial genus Aromatoleum comprises facultative denitrifiers specialized in the anaerobic degradation of recalcitrant organic compounds (aromatic and terpenoid). This study reports on the complete and manually annotated genomes of Ar. petrolei ToN1<sup>T</sup> (5.41 Mbp) and Ar. bremense PbN1<sup>T</sup> (4.38 Mbp), which cover the phylogenetic breadth of the genus Aromatoleum together with previously genome sequenced Ar. aromaticum EbN1<sup>T</sup> [Rabus et al., Arch Microbiol. 2005 Jan;183(1):27–36]. The gene clusters for the anaerobic degradation of aromatic and terpenoid (strain ToN1<sup>T</sup> only) compounds are scattered across the genomes of strains ToN1<sup>T</sup> and PbN1<sup>T</sup>. The richness in mobile genetic elements is shared with other Aromatoleum spp., substantiating that horizontal gene transfer should have been a major driver in shaping the genomes of this genus. The composite catabolic network of strains ToN1<sup>T</sup> and PbN1<sup>T</sup> comprises 88 proteins, the coding genes of which occupy 86.1 and 76.4 kbp (1.59 and 1.75%) of the respective genome. The strain-specific gene clusters for anaerobic degradation of ethyl-/propylbenzene (strain PbN1<sup>T</sup>) and toluene/monoterpenes (strain ToN1<sup>T</sup>) share high similarity with their counterparts in Ar. aromaticum strains EbN1<sup>T</sup> and pCyN1, respectively. Glucose is degraded via the ED-pathway in strain ToN1<sup>T</sup>, while gluconeogenesis proceeds via the reverse EMP-pathway in strains ToN1<sup>T</sup>, PbN1<sup>T</sup>, and EbN1<sup>T</sup>. The diazotrophic, endophytic lifestyle of closest related genus Azoarcus is known to be associated with nitrogenase and type-6 secretion system (T6SS). By contrast, strains ToN1<sup>T</sup>, PbN1<sup>T</sup>, and EbN1<sup>T</sup> lack nif genes for nitrogenase (including cofactor synthesis and enzyme maturation). Moreover, strains PbN1<sup>T</sup> and EbN1<sup>T</sup> do not possess tss genes for T6SS, while strain ToN1<sup>T</sup> does and facultative endophytic “Aromatoleum” sp. CIB is known to even have both. These findings underpin the functional heterogeneity among Aromatoleum members, correlating with the high plasticity of their genomes.
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