Production of indole-3-acetic acid, aromatic amino acid aminotransferase activities and plant growth promotion by Pantoea agglomerans rhizosphere isolates

Phytohormone-like acting compounds previously have been suggested to be involved in the phytostimulatory action exerted by the plant-beneficial rhizobacterium Bacillus amyloliquefaciens FZB42. Analyses by high-performance liquid chromatography and gas chromatography-mass spectrometry performed with culture filtrates of FZB42 demonstrated the presence of indole-3-acetic acid (IAA), corroborating it as one of the pivotal plant-growth-promoting substances produced by this bacterium. In the presence of 5 mM tryptophan, a fivefold increase in IAA secretion was registered. In addition, in the trp auxotrophic strains E101 (ΔtrpBA) and E102 (ΔtrpED), and in two other strains bearing knockout mutations in genes probably involved in IAA metabolism, E103 (ΔysnE, putative IAA transacetylase) and E105 (ΔyhcX, putative nitrilase), the concentration of IAA in the culture filtrates was diminished. Three of these mutant strains were less efficient in promoting plant growth, indicating that the Trp-dependent synthesis of auxins and plant growth promotion are functionally related in B. amyloliquefaciens.

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Genome Sequencing of Pantoea agglomerans C1 Provides Insights into Molecular and Genetic Mechanisms of Plant Growth-Promotion and Tolerance to Heavy Metals

Microorganisms ◽

10.3390/microorganisms8020153 ◽

2020 ◽

Vol 8 (2) ◽

pp. 153 ◽

Cited By ~ 3

Author(s):

Francesca Luziatelli ◽

Anna Grazia Ficca ◽

Mariateresa Cardarelli ◽

Francesca Melini ◽

Andrea Cavalieri ◽

...

Keyword(s):

Heavy Metals ◽

Plant Growth ◽

Plant Growth Promotion ◽

Plant Pathogens ◽

Growth Promotion ◽

Pantoea Agglomerans ◽

Toxic Heavy Metals ◽

Circular Chromosome ◽

Plant Growth Promoting ◽

Genetic Mechanisms

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.

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