A transcriptional regulator of the LuxR-UhpA family, FlcA, controls flocculation and wheat root surface colonization by Azospirillum brasilense Sp7

Mol Plant Microbe Interact. 1998 Mar;11(3):177-87. doi: 10.1094/MPMI.1998.11.3.177.


Genetic complementation of a spontaneous mutant, impaired in flocculation, Congo red binding, and colonization of root surface, led to the identification of a new regulatory gene in Azospirillum brasilense Sp7, designated flcA. The deduced amino acid sequence of flcA shared high similarity with a family of transcriptional activators of the LuxR-UphA family. The most significant match was with the AgmR protein, an activator for glycerol metabolism in Pseudomonas aeruginosa. Derivatives of Sp7 resulting from site-directed Tn5 mutagenesis in the flcA coding sequence were constructed by marker exchange. Characterization of the resulting mutant strains showed that flcA controls the production of capsular polysaccharides, the flocculation process in culture, and the colonization of the root surface of wheat. This study provides new information on the genetic control of the mechanism of plant root colonization by Azospirillum.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Azospirillum brasilense / genetics
  • Azospirillum brasilense / physiology*
  • Azospirillum brasilense / ultrastructure
  • Bacterial Proteins / chemistry
  • DNA-Binding Proteins / chemistry
  • Genes, Fungal
  • Genes, Regulator
  • Genetic Complementation Test
  • Genotype
  • Molecular Sequence Data
  • Multigene Family
  • Mutation
  • Phenotype
  • Plant Roots
  • Repressor Proteins / chemistry
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Trans-Activators / chemistry
  • Transcription Factors / chemistry
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism*
  • Triticum / microbiology*


  • Bacterial Proteins
  • DNA-Binding Proteins
  • FlcA protein, Azospirillum brasilense
  • Repressor Proteins
  • Trans-Activators
  • Transcription Factors
  • UhpA protein, Bacteria
  • LuxR autoinducer binding proteins

Associated data

  • GENBANK/Y12363