Open AccessArabinose content of extracellular polysaccharide plays a role in cell aggregation of Azospirillum brasilense
Author(s) -
BahatSamet Efrat,
CastroSowinski Susana,
Okon Yaacov
Publication year - 2004
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.2004.tb09696.x
Subject(s) - azospirillum brasilense , arabinose , extracellular , polysaccharide , biochemistry , rhamnose , bacteria , mutant , fructose , bacteroides fragilis , biology , chemistry , microbiology and biotechnology , microbial inoculant , xylose , fermentation , gene , genetics , antibiotics
Extracellular polysaccharides play an important role in aggregation and surface colonization of plant‐associated bacteria. In this work, we report the time course production and monomer composition of the exopolysaccharide (EPS) produced by wild type strain and several mutants of the plant growth promoting rhizobacterium (PGPR) Azospirillum brasilense . In a fructose synthetic medium, wild type strain Sp7 produced a glucose‐rich EPS during exponential phase growth and an arabinose‐rich EPS during stationary and death phase growth. d ‐glucose or l ‐arabinose did not support cell growth as sole carbon sources. However, glucose and arabinose‐rich EPSs, when used as carbon source, supported bacterial growth. Cell aggregation of Sp7 correlated with the synthesis of arabinose‐rich EPS. exoB (UDP‐glucose 4′‐epimerase), exoC (phosphomannomutase) and phbC (poly‐β‐hydroxyburyrate synthase) mutant strains, under tested conditions, produced arabinose‐rich EPS and exhibited highly cell aggregation capability. A mutant defective in LPS production (dTDP 4‐rhamnose reductase; rmlD ) produced glucose‐rich EPS and did not aggregate. These results support that arabinose content of EPS plays an important role in cell aggregation. Cell aggregation appears to be a time course phenomenon that takes place during reduced metabolic cell activity. Thus, aggregation could constitute a protected model of growth that allows survival in a hostile environment. The occurrence of exoC and rmlD was detected in several species of Azospirillum .