Surface Characteristics of<i>Azospirillum brasilense</i>in Relation to Cell Aggregation and Attachment to Plant Roots

Burdman, Saul; Okon, Yaacov; Jurkevitch, Édouard

doi:10.1080/10408410091154200

Cited by 117 publications

(82 citation statements)

References 61 publications

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“…Azospirilla are known for their capacity to aggregate and flocculate under diverse stress conditions. Previous studies have suggested the involvement of extracellular polysaccharides in cell aggregation (5). The concentrations of EPS produced by four different strains of A. brasilense differing in their ability to aggregate increased with the extent of aggregation (3).…”

Section: Discussionmentioning

confidence: 98%

Identification and Isolation of Genes Involved in Poly(β-Hydroxybutyrate) Biosynthesis in Azospirillum brasilense and Characterization of a phbC Mutant

Kadouri

Burdman

Jurkevitch

et al. 2002

Appl Environ Microbiol

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Like many other prokaryotes, rhizobacteria of the genus Azospirillum produce high levels of poly(␤-hydroxybutyrate) (PHB) under suboptimal growth conditions. Utilization of PHB by bacteria under stress has been proposed as a mechanism that favors their compatible establishment in competitive environments, thus showing great potential for the improvement of bacterial inoculants for plants and soils. The three genes that are considered to be essential in the PHB biosynthetic pathway, phbA (␤-ketothiolase), phbB (acetoacetyl coenzyme A reductase), and phbC (PHB synthase), were identified in Azospirillum brasilense strain Sp7, cloned, and sequenced. The phbA, -B, and -C genes were found to be linked together and located on the chromosome. An A. brasilense phbC mutant was obtained by insertion of a kanamycin resistance cassette within the phbC gene. No PHB production was detected in this mutant. The capability of the wild-type strain to endure starvation conditions was higher than that of the mutant strain. However, motility, cell aggregation, root adhesion, and exopolysaccharide (EPS) and capsular polysaccharide (CPS) production were higher in the phbC mutant strain than in the wild type.

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Section: Discussionmentioning

confidence: 98%

Identification and Isolation of Genes Involved in Poly(β-Hydroxybutyrate) Biosynthesis in Azospirillum brasilense and Characterization of a phbC Mutant

Kadouri

Burdman

Jurkevitch

et al. 2002

Appl Environ Microbiol

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“…Differences in the exopolysaccharide and capsular polysaccharide contents between wild-type and mutant strains can also explain the ability to aggregate displayed by the latter strain in this study. Azospirilla are known for their capacity to aggregate and flocculate under diverse stress conditions, and previous studies have shown that extracellular polysaccharides are involved in cell aggregation (1,3,21,32). Although the mutant strain's ability to adhere to roots is greater than that of the wild type, no difference in root colonization was observed between the two strains.…”

Section: Discussionmentioning

confidence: 99%

“…This method was shown to be more sensitive and more specific than the Salkowski-based colorimetric technique (10). For the reaction, 1 ml of reagent R1, consisting of 12 g of FeCl 3 per liter in 7.9 M H 2 SO 4 , was added to 1 ml of a sample supernatant, mixed well, and left in the dark for 30 min at room temperature. Absorbance was measured at 530 nm.…”

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confidence: 99%

Involvement of the Reserve Material Poly-β-Hydroxybutyrate inAzospirillum brasilenseStress Endurance and Root Colonization

Kadouri

Jurkevitch

Okon

2003

Appl Environ Microbiol

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163

114

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When grown under suboptimal conditions, rhizobacteria of the genus Azospirillum produce high levels of poly-␤-hydroxybutyrate (PHB). Azospirillum brasilense strain Sp7 and a phbC (PHB synthase) mutant strain in which PHB production is impaired were evaluated for metabolic versatility, for the ability to endure various stress conditions, for survival in soil inoculants, and for the potential to promote plant growth. The carbon source utilization data were similar for the wild-type and mutant strains, but the generation time of the wild-type strain was shorter than that of the mutant strain with all carbon sources tested. The ability of the wild type to endure UV irradiation, heat, osmotic pressure, osmotic shock, and desiccation and to grow in the presence of hydrogen peroxide was greater than that of the mutant strain. The motility and cell aggregation of the mutant strain were greater than the motility and cell aggregation of the wild type. However, the wild type exhibited greater chemotactic responses towards attractants than the mutant strain exhibited. The wild-type strain exhibited better survival than the mutant strain in carrier materials used for soil inoculants, but no difference in the ability to promote plant growth was detected between the strains. In soil, the two strains colonized roots to the same extent. It appears that synthesis and utilization of PHB as a carbon and energy source by A. brasilense under stress conditions favor establishment of this bacterium and its survival in competitive environments. However, in A. brasilense, PHB production does not seem to provide an advantage in root colonization under the conditions tested.A wide variety of microorganisms are known to produce intracellular energy and carbon storage compounds that generally are described as poly-␤-hydroxybutyrate (PHB). It has been found that in most cases the polymers are polyhydroxyalkanoates (PHAs) comprising copolymers that contain different alkyl groups at the ␤ position (41).The gram-negative nitrogen-fixing rhizobacterium Azospirillum brasilense lives in close association with plant roots, where it has beneficial effects on plant growth and the yields of many crops of agronomic importance (25,26). Enzymes involved in the synthesis, accumulation, and degradation of PHAs in A. brasilense have been examined in detail (35)(36)(37). It has been shown that in contrast to other bacterial species, A. brasilense does not produce copolymers of hydroxyalkanoates; rather, it produces only homopolymers of PHB (15).Although mutants unable to synthesize PHAs have been isolated and genetically engineered in several bacterial species (4,13,14,27,28,33,42), most PHA-negative mutants have been examined to determine their effects on symbiosis and on cellular metabolism (4, 27, 42). The ecological role played by PHA in bacteria under stress conditions has not been generally investigated. Understanding the role played by PHAs as internal storage polymers is of fundamental importance in microbial ecology. The accumulation, degradation, an...

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“…EPS and CPS play a major role in the interaction of A. brasilense with plant roots (Jofré et al, 2004;Burdman et al, 2000b). It has been proposed that A. brasilense cells adhere to plant roots in two steps: while the first step, likely mediated by polar flagella, is relatively rapid and reversible, in the second step, named the anchoring phase, the cells are anchored firmly and irreversibly to the plant roots, in a process mediated by EPS and CPS (Michiels et al, 1991;Moens & Vanderleyden, 1996;Steenhoudt & Vanderleyden, 2000).…”

Section: Introductionmentioning

confidence: 99%

The Azospirillum brasilense Sp7 noeJ and noeL genes are involved in extracellular polysaccharide biosynthesis

et al. 2009

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The Azospirillum brasilense Sp7 noeJ and noeL genes are involved in extracellular polysaccharide biosynthesis Azospirillum brasilense is a plant root-colonizing bacterium that exerts beneficial effects on the growth of many agricultural crops. Extracellular polysaccharides of the bacterium play an important role in its interactions with plant roots. The pRhico plasmid of A. brasilense Sp7, also named p90, carries several genes involved in synthesis and export of cell surface polysaccharides. We generated two Sp7 mutants impaired in two pRhico-located genes, noeJ and noeL, encoding mannose-6-phosphate isomerase and GDP-mannose 4,6-dehydratase, respectively. Our results demonstrate that in A. brasilense Sp7, noeJ and noeL are involved in lipopolysaccharide and exopolysaccharide synthesis. noeJ and noeL mutant strains were significantly altered in their outer membrane and cytoplasmic/periplasmic protein profiles relative to the wild-type strain. Moreover, both noeJ and noeL mutations significantly affected the bacterial responses to several stresses and antimicrobial compounds. Disruption of noeL, but not noeJ, affected the ability of the A. brasilense Sp7 to form biofilms. The pleiotropic alterations observed in the mutants could be due, at least partially, to their altered lipopolysaccharides and exopolysaccharides relative to the wild-type.

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Surface Characteristics ofAzospirillum brasilensein Relation to Cell Aggregation and Attachment to Plant Roots

Cited by 117 publications

References 61 publications

Identification and Isolation of Genes Involved in Poly(β-Hydroxybutyrate) Biosynthesis in Azospirillum brasilense and Characterization of a phbC Mutant

Identification and Isolation of Genes Involved in Poly(β-Hydroxybutyrate) Biosynthesis in Azospirillum brasilense and Characterization of a phbC Mutant

Involvement of the Reserve Material Poly-β-Hydroxybutyrate inAzospirillum brasilenseStress Endurance and Root Colonization

The Azospirillum brasilense Sp7 noeJ and noeL genes are involved in extracellular polysaccharide biosynthesis

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