Abstract
Burkholderia phytofirmans PsJN is a naturally occurring plant-associated bacterial endophyte that effectively colonizes a wide range of plants and stimulates their growth and vitality. Here we analyze whole genomes, of PsJN and of eight other endophytic bacteria. This study illustrates that a wide spectrum of endophytic life styles exists. Although we postulate the existence of typical endophytic traits, no unique gene cluster could be exclusively linked to the endophytic lifestyle. Furthermore, our study revealed a high genetic diversity among bacterial endophytes as reflected in their genotypic and phenotypic features. B. phytofirmans PsJN is in many aspects outstanding among the selected endophytes. It has the biggest genome consisting of two chromosomes and one plasmid, well-equipped with genes for the degradation of complex organic compounds and detoxification, e.g., 24 glutathione-S-transferase (GST) genes. Furthermore, strain PsJN has a high number of cell surface signaling and secretion systems and harbors the 3-OH-PAME quorum-sensing system that coordinates the switch of free-living to the symbiotic lifestyle in the plant-pathogen R. solanacearum. The ability of B. phytofirmans PsJN to successfully colonize such a wide variety of plant species might be based on its large genome harboring a broad range of physiological functions.
Highlights
The growing demand for alternatives to the use of agrochemicals in agricultural production has increased interest in harnessing benefits of plants’ colonization by ameliorating microorganisms
Ninety-two percent (6807) of all CDSs in the genome of B. phytofirmans PsJN showed highest homology with Betaproteobacteria (Weilharter et al, 2011), and 4547 genes (61.4%) were most closely related to B. xenovorans LB400 (Chain et al, 2006), with over 3371 genes showing more than 90% sequence homology
Based on comparative analyses of eight genomes of bacterial endophytes we addressed the question of occurrence of the overall features typical for, and required for the establishment of endophytic lifestyles by bacteria
Summary
The growing demand for alternatives to the use of agrochemicals in agricultural production has increased interest in harnessing benefits of plants’ colonization by ameliorating microorganisms. Bacterial endophytes residing inside plants without harming their host (Wilson, 1995) have received particular attention as many of them support plant growth, and improve their health status and adaptation to changes in edaphic conditions (Ryan et al, 2007; Compant et al, 2010b). Over the past few decades our understanding of the role of bacteria in the plant rhizosphere has dramatically advanced, we still have only a limited knowledge of bacterial traits determining internal colonization of host plants and their endophytic life. The identified determinants of this competitive ability include production of antimicrobial compounds, detoxification of reactive oxygen species (ROS), and plant secondary metabolites by anti-oxidative enzymes, ring-cleaving by dioxygenases, a presence of efflux pumps (Martinez et al, 2009; Barret et al, 2011), and/or efficient acquisition of nutrients facilitated by various membrane transporters and excreted siderophores (Loaces et al, 2011)
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