Whole-genome analysis of Azoarcus sp. strain CIB provides genetic insights to its different lifestyles and predicts novel metabolic features

The genomic features of Azoarcus sp. CIB reflect its most distinguishing phenotypes as a diazotroph, facultative anaerobe, capable of degrading either aerobically and/or anaerobically a wide range of aromatic compounds, including some toxic hydrocarbons such as toluene and m-xylene, as well as its endophytic lifestyle. The analyses of its genome have expanded the catabolic potential of strain CIB toward common natural compounds, such as certain diterpenes, that were not anticipated as carbon sources. The high number of predicted solvent efflux pumps and heavy metal resistance gene clusters has provided the first evidence for two environmentally relevant features of this bacterium that remained unknown. Genome mining has revealed several gene clusters likely involved in the endophytic lifestyle of strain CIB, opening the door to the molecular characterization of some plant growth promoting traits. Horizontal gene transfer and mobile genetic elements appear to have played a major role as a mechanism of adaptation of this bacterium to different lifestyles. This work paves the way for a systems biology-based understanding of the abilities of Azoarcus sp. CIB to integrate aerobic and anaerobic metabolism of aromatic compounds, tolerate stress conditions, and interact with plants as an endophyte of great potential for phytostimulation and phytoremediation strategies. Comparative genomics provides an Azoarcus pan genome that confirms the global metabolic flexibility of this genus, and suggests that its phylogeny should be revisited.