TY - JOUR
T1 - Aggregation in Azospirillum brasilense
T2 - Effects of chemical and physical factors and involvement of extracellular components
AU - Burdman, Saul
AU - Jurkevitch, Edouard
AU - Schwartsburd, Boris
AU - Hampel, Michal
AU - Okon, Yaacov
PY - 1998/7
Y1 - 1998/7
N2 - 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-B-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.
AB - 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-B-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.
KW - Aggregation
KW - Azospirillum brasilense
KW - Exopolysaccharides
KW - Flocculation
UR - http://www.scopus.com/inward/record.url?scp=0031825203&partnerID=8YFLogxK
U2 - 10.1099/00221287-144-7-1989
DO - 10.1099/00221287-144-7-1989
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C2 - 9695932
AN - SCOPUS:0031825203
SN - 1350-0872
VL - 144
SP - 1989
EP - 1999
JO - Microbiology
JF - Microbiology
IS - 7
ER -