Aggregation in Azospirillum brasilense: effects of chemical and physical factors and involvement of extracellular components.
A medium for consistent induction of aggregation of Azospirillum brasilense cells was developed and used to study the effects of chemical and physical factors as well as extracellular components involved in this phenomenon. Growth of A. brasilense strain Cd in a high C:N medium using fructose and ammonium chloride as C and N sources, respectively, resulted in flocculation visible to the naked eye after 24 h. No cell aggregates were formed after 72 h growth in low C:N medium. Aggregating cells, but not cells grown under low C:N, accumulated high amounts of poly-beta-hydroxybutyrate and the cell envelope contained a well-defined electron-dense layer outside the outer membrane. Suspending the aggregates in 0.2 or 0.5 M urea was the only treatment effective for disrupting aggregates. The concentration of exopolysaccharide produced by four different strains of A. brasilense, differing in their capacity to aggregate, strongly correlated with the extent of aggregation. Electrophoretic protein profiles from different fractions of aggregating and non-aggregating cells were compared. Differences were observed in the pattern of low-molecular-mass proteins and in the polar flagellin that has previously been proposed to be involved in adhesion processes. However, a mutant lacking both lateral and polar flagella showed the strongest aggregation. The involvement of polysaccharides and/or proteins in aggregation of A. brasilense is discussed.
Department of Plant Pathology and Microbiology, and The Otto Warburg Center for Agricultural Biotechnology, The Hebrew University of JerusalemRehovot 76100Israel.
Saul
S
Burdman
Department of Plant Pathology and Microbiology, and The Otto Warburg Center for Agricultural Biotechnology, The Hebrew University of JerusalemRehovot 76100Israel.
Edouard
E
Jurkevitch
Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of JerusalemRehovot 76100Israel.
Boris
B
Schwartsburd
Department of Plant Pathology and Microbiology, and The Otto Warburg Center for Agricultural Biotechnology, The Hebrew University of JerusalemRehovot 76100Israel.
Michal
M
Hampel
Department of Plant Pathology and Microbiology, and The Otto Warburg Center for Agricultural Biotechnology, The Hebrew University of JerusalemRehovot 76100Israel.
Yaacov
Y
Okon
D000643:Ammonium Chloride / Q000494:pharmacology; D015806:Azospirillum brasilense / Q000187:drug effects / Q000502:physiology*; D001425:Bacterial Outer Membrane Proteins / Q000302:isolation & purification; D001426:Bacterial Proteins / Q000032:analysis / Q000378:metabolism; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D005632:Fructose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006885:Hydroxybutyrates / Q000032:analysis; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D011134:Polysaccharides / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology; D013997:Time Factors; D014508:Urea / Q000494:pharmacology
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D006885:Hydroxybutyrates; D011134:Polysaccharides; D000643:Ammonium Chloride; D005632:Fructose; D014508:Urea