2006, pp 873-891

The Genera Azoarcus, Azovibrio, Azospira and Azonexus

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Introduction

The genera Azoarcus, Azospira, Azovibrio and Azonexus harbor mostly nitrogen-fixing Betaproteobacteria. In their first taxonomic description, several strains which were later assigned to the genera Azovibrio, Azospira (Reinhold-Hurek et al., 1993) and Azonexus (Hurek et al., 1997b) were included in the genus Azoarcus sensu lato. Therefore, they are discussed in one chapter. Except for one strain, all these diazotrophic bacteria had been isolated from a similar source, roots of a pioneer grass in Pakistan or fungal resting stages from the same field; they had many physiological features in common, and they were phylogenetically related. Therefore, three groups of bacteria were included into Azoarcus although they were located on the Azoarcus rRNA branch at low Tm(e) values (Reinhold-Hurek et al., 1993) or showed a low 16S rDNA similarity (Hurek et al., 1997b). Isolation of additional strains, which made possible a better phenotypic description, and sequencing of ...