Enterobacter sp. 638 is an endophytic plant growth promoting gamma-proteobacterium that was isolated from the stem of poplar (Populus trichocarpaxdeltoides cv. H11-11), a potentially important
biofuel feed stock plant. The Enterobacter sp. 638 genome sequence reveals the presence of a 4,518,712 bp chromosome and a 157,749 bp plasmid (pENT638-1). Genome annotation and comparative genomics allowed the identification of an extended set of genes specific to the plant niche adaptation of this bacterium. This includes genes that code for putative
proteins involved in survival in the rhizosphere (to cope with oxidative stress or uptake of nutrients released by plant roots), root adhesion (pili, adhesion,
hemagglutinin,
cellulose biosynthesis), colonization/establishment inside the plant (chemiotaxis, flagella,
cellobiose phosphorylase), plant protection against fungal and
bacterial infections (
siderophore production and synthesis of the antimicrobial compounds 4-hydroxybenzoate and
2-phenylethanol), and improved poplar growth and development through the production of the
phytohormones indole acetic acid,
acetoin, and
2,3-butanediol. Metabolite analysis confirmed by quantitative RT-PCR showed that, the production of
acetoin and
2,3-butanediol is induced by the presence of
sucrose in the growth medium. Interestingly, both the genetic determinants required for
sucrose metabolism and the synthesis of
acetoin and
2,3-butanediol are clustered on a genomic island. These findings point to a close interaction between Enterobacter sp. 638 and its poplar host, where the availability of
sucrose, a major plant
sugar, affects the synthesis of plant growth promoting
phytohormones by the endophytic bacterium. The availability of the genome sequence, combined with metabolome and transcriptome analysis, will provide a better understanding of the synergistic interactions between poplar and its growth promoting endophyte Enterobacter sp. 638. This information can be further exploited to improve establishment and sustainable production of poplar as an energy feedstock on marginal, non-agricultural
soils using endophytic bacteria as growth promoting agents.