Abstract
Distinctive strains of Pantoea are used as soil inoculants for their ability to promote plant growth. Pantoea agglomerans strain C1, previously isolated from the phyllosphere of lettuce, can produce indole-3-acetic acid (IAA), solubilize phosphate, and inhibit plant pathogens, such as Erwinia amylovora. In this paper, the complete genome sequence of strain C1 is reported. In addition, experimental evidence is provided on how the strain tolerates arsenate As (V) up to 100 mM, and on how secreted metabolites like IAA and siderophores act as biostimulants in tomato cuttings. The strain has a circular chromosome and two prophages for a total genome of 4,846,925-bp, with a DNA G+C content of 55.2%. Genes related to plant growth promotion and biocontrol activity, such as those associated with IAA and spermidine synthesis, solubilization of inorganic phosphate, acquisition of ferrous iron, and production of volatile organic compounds, siderophores and GABA, were found in the genome of strain C1. Genome analysis also provided better understanding of the mechanisms underlying strain resistance to multiple toxic heavy metals and transmission of these genes by horizontal gene transfer. Findings suggested that strain C1 exhibits high biotechnological potential as plant growth-promoting bacterium in heavy metal polluted soils.
Highlights
Soils are a natural source of heavy metals (HM), but geologic and anthropogenic activities have increased concentration thereof in soil, water and living systems [1]
Average nucleotide identity analysis was performed between P. agglomerans C1 and other Pantoea isolates included in the phylogenetic tree, using an on-line ANI calculator [26], and the presence of plasmid replicons or prophages was determined using the PlasmidFinder tool [27] and PHAge Search Tool Enhanced Release (PHASTER) [28,29], respectively
Minimal inhibitory concentration (MIC) of arsenite (As(III)) and arsenate (As(V)) for P. agglomerans strain C1 was determined in 20 mL cultures grown in 100 mL Erlenmeyer flasks at 30 ◦C in agitation (180 rpm)
Summary
Soils are a natural source of heavy metals (HM), but geologic and anthropogenic activities have increased concentration thereof in soil, water and living systems [1]. PGPB enhance the growth of plants through various plant growth-promoting (PGP) traits (e.g., phosphate solubilization, production of indole-3-acetic acid, siderophores, ammonia, hydrogen cyanide and nitrogen fixation) [3,4,5,6] They have the potential for metal detoxification and mitigation of plant’s stress in polluted environment. It has been demonstrated that the arsenic resistance gene cluster that confers arsenic resistance through arsenate reduction and arsenite efflux (arsRBC or arsRBCH) occurs in the genome of several strains belonging to different Pantoea species [14] Based on these findings, it is important to understand the impact that arsenic tolerant Pantoea strains can have on reducing plant stress and improving plant growth performance. Microorganisms 2020, 8, 153 into the potential of the P. agglomerans strain C1 to both survive in arsenate-contaminated soil and stimulate plant growth
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