Novel insights into ecological distribution and plant growth promotion by nitrogen-fixing endophytes – how specialised are they?

The genome sequence of Azoarcus olearis DQS-4T, reveals that it is highly similar to the model Azoarcus strain BH72, with almost 99% average nucleotide identity encoding a highly similar proteome, thus placing the two strains within the same species. The isolation and characterisation of a strain from an industrial location, highly similar to that of BH72, which was previously thought to exist only within the plant environment, is of considerable interest from the ecological point of view and raises the possibility that related plant endophytic bacteria are far more widespread in the environment than originally considered. Overall these findings raise a number of crucial questions concerning the habitat of Azoarcus strains, the relationship between nif gene organisation and plant growth promotion, the precise determinants required for plant colonisation and the importance of physiological traits to the ecology of Azoarcus species.