Role of the O-Antigen of Lipopolysaccharide, and Possible Roles of Growth Rate and of NADH:ubiquinone Oxidoreductase (nuo) in Competitive Tomato Root-Tip Colonization by Pseudomonas fluorescens WCS365

Abstract

Colonization-defective, transposon-induced mutants of the efficient root colonizer Pseudomonas fluorescens WCS365 were identified with a gnotobiotic system. Most mutants were impaired in known colonization traits, i.e., prototrophy for amino acids, motility, and synthesis of the O-antigen of LPS (lipopolysaccharide). Mutants lacking the O-antigen of LPS were impaired in both colonization and competitive growth whereas one mutant (PCL1205) with a shorter O-antigen chain was defective only in colonization ability, suggesting a role for the intact O-antigen of LPS in colonization. Eight competitive colonization mutants that were not defective in the above-mentioned traits colonized the tomato root tip well when inoculated alone, but were defective in competitive root colonization of tomato, radish, and wheat, indicating they contained mutations affecting host range. One of these eight mutants (PCL1201) was further characterized and contains a mutation in a gene that shows homology to the Escherichia coli nuo4 gene, which encodes a subunit of one of two known NADH:ubiquinone oxidoreductases. Competition experiments in an oxygen-poor medium between mutant PCL1201 and its parental strain showed a decreased growth rate of mutant PCL1201. The requirement of the nuo4 gene homolog for optimal growth under conditions of oxygen limitation suggests that the root-tip environment is micro-aerobic. A mutant characterized by a slow growth rate (PCL1216) was analyzed further and contained a mutation in a gene with similarity to the E. coli HtrB protein, a lauroyl transferase that functions in lipid A biosynthesis.

Analysis of Pseudomonas fluorescens F113 genes implicated in flagellar filament synthesis and their role in competitive root colonization

“…It is already known that bacterial motility is important in the colonization of the rhizosphere, since different non-motile mutants from P. fluorescens strain WCS374 were severely impaired in colonization (Dekkers et al, 1998a). In fact, the non-motile mutants belong to the most defective competitive class of colonization mutants (Dekkers et al, 1998b;Chin-a-Woeng et al, 2000).…”

“…The defect was larger at sites more distant from the inoculation site, in the root systems formed after the bacterial inoculation (De Weger et al, 1987;Dekkers et al, 1998b; Chin-a-Woeng et al, 2000). Furthermore motility-impaired mutants of Pseudomonas chlororaphis PCL1391 do not reduce the The GenBank/EMBL/DDBJ accession number for the 6?5 kb region sequence reported in this paper is AF399739.…”

“…It is already known that bacterial motility is important in the colonization of the rhizosphere, since different non-motile mutants from P. fluorescens strain WCS374 were severely impaired in colonization (Dekkers et al, 1998a). In fact, the non-motile mutants belong to the most defective competitive class of colonization mutants (Dekkers et al, 1998b; Chin-a-Woeng et al, 2000).In this work we have characterized a genetic region of P. fluorescens F113 implicated in the synthesis of the flagellar filament and we have shown that the genetic organization is similar to other pseudomonads but differs from the P. aeruginosa PAK and DG1 strains because they have two copies of the fliS gene. The first gene in the region, fliC, encodes a type b flagellin, the main structural protein of the flagellar filament.…”

Cell Density-Dependent Gene Contributes to Efficient Seed Colonization by Pseudomonas putida KT2440

“…Efficient rhizosphere colonization is one of the keys to the success of biocontrol processes (6,7). Elements known to participate in bacterial root colonization include NADH dehydrogenase I, flagellar motility, chemotaxis, lipopolysaccharide, and type IV pili (12,16,47,48,50,51). Mutants of Pseudomonas fluorescens unable to synthesize certain vitamins and amino acids also show reduced colonization capacity, indicating that the amounts of these compounds found in the rhizosphere are not sufficient to overcome some auxotrophies (28).…”

Root Colonization and Quorum Sensing are the Driving forces of Plant Growth Promoting Rhizobacteria (pgpr) for Growth Promotion

“…The MOMP of Azospirillum brasilense showed stronger adhesion factor to extracts of cereals than extracts of legumes and tomatoes, and may act as an adhesion involved in root adsorption and cell aggregation of the bacterium [73]. Bacterial lipopolysaccharides (LPS), in particular the O-antigen chain, can also contribute to root colonization [74,75]. However, it is strain dependent since the O-antigenic side chain of P. fluorescens WCS374 does not contribute to potato root adhesion [76], whereas the O-antigen chain of P. fluorescens PCL1205 is involved in tomato root colonization [75].…”