Does Azoarcus sp. Fix Nitrogen with Monocots?

Bacteria assigned to the genus Azoarcus are a genotypically divergent collection of N2-fixing microorganisms clustering in more than seven groups distinct at the species level. They are ubiquitous and represent soil, fungal, as well as plant isolates. Up to now the complete set of plant-associated species has been obtained only from the rhizosphere of Kallar grass, grown on a frequently flooded, low-fertility soil in the Punjab of Pakistan. Application of phylogenetic analysis to DNA isolated from environmental samples demonstrated that Azoarcus also occurs in rice grown in Japan. The relevance of this finding lies in a potential interest in diazotrophs such as Azoarcus for sustainable agriculture: (i) they invade roots, possibly mediated by their own cellulases, spread inside plants, and live there endophytically. (ii) They are capable of extremely active and efficient nitrogen fixation in laboratory culture, (iii) and they are also capable of expression of nif genes inside the roots of uninoculated, soil-grown plants.