Genomic insights into the versatility of the plant growth-promoting bacterium Azospirillum amazonense

Fernando H Sant'Anna,Luciano A Reolon,Franciele M Siqueira,Ana Tr Vasconcelos,Maicon Rs Machado,Irene S Schrank,Luiz Gp Almeida,Ricardo Cecagno

doi:10.1186/1471-2164-12-409

Abstract

BackgroundThe species Azospirillum amazonense belongs to a well-known genus of plant growth-promoting bacteria. This bacterium is found in association with several crops of economic importance; however, there is a lack of information on its physiology. In this work, we present a comprehensive analysis of the genomic features of this species.ResultsGenes of A. amazonense related to nitrogen/carbon metabolism, energy production, phytohormone production, transport, quorum sensing, antibiotic resistance, chemotaxis/motility and bacteriophytochrome biosynthesis were identified. Noteworthy genes were the nitrogen fixation genes and the nitrilase gene, which could be directly implicated in plant growth promotion, and the carbon fixation genes, which had previously been poorly investigated in this genus. One important finding was that some A. amazonense genes, like the nitrogenase genes and RubisCO genes, were closer phylogenetically to Rhizobiales members than to species of its own order.ConclusionThe species A. amazonense presents a versatile repertoire of genes crucial for its plant-associated lifestyle.

Highlights

The species Azospirillum amazonense belongs to a well-known genus of plant growth-promoting bacteria
Taxonomic features of A. amazonense In this study, a phylogenetic tree was constructed using the 16S rDNA sequences from microorganisms belonging to the orders Rhodospirillales and Rhizobiales (Figure 1)
The outermost clade containing all the Azospirillum species divides in two main subclades: one containing A. amazonense, A. irakense, Rhodocista pekingensis and R. centenum, and another containing the other Azospirillum species. This result is in agreement with previous studies, showing the close evolutionary relationship between A. amazonense and R. centenum [12,13,14], and is supported by the greater number of A. amazonense genes (22%) with best BLAST hits (KEGG Database) to R. centenum genes

Summary

Introduction

The species Azospirillum amazonense belongs to a well-known genus of plant growth-promoting bacteria. The genus Azospirillum (a-proteobacteria class) encompasses free-living bacteria that can improve the growth of many economically important plants, mainly cereals (for an extensive review, see [1]) These microorganisms are considered as plant growth-promoting rhizobacteria (PGPR). Species of this genus are widely distributed in nature, living in soils of tropical, subtropical and temperate regions all over the world Several aspects of their physiology seem to be related to a plant stimulatory effect, notably their ability to synthesize phytohormones. Further studies revealed its broad ecological distribution, as it is found in association with the roots of gramineous plants like rice, maize, sugarcane and sorghum [5,6] This species is phylogenetically closer to Azospirillum irakense and Rhodospirillum centenum ( known as Rhodocista centenaria) than to A. brasilense. A. amazonense can use sucrose as a sole carbon source and is better adapted to acid environments [6]

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