f Involvement of outer-membrane proteins in the aggregation of Azospirillum brasilense
- Authors: Saul Burdman, Edouard Jurkevitch, Boris Schwartsburd, Yaacov Okon
- Author for correspondence: Yaacov Okon. Tel: +972 8 9481216. Fax: +972 8 9466794. e-mail: email@example.com
- Microbiology, May 1999 145: 1145-1152, doi: 10.1099/13500872-145-5-1145
- Subject: Genetics And Molecular Biology
- Published Online:
A bioassay was developed to investigate biological factors involved in the aggregation of Azospirillum brasilense strain Cd. Cells were grown for 24 h under aggregation-inducing and non-aggregation-inducing conditions (high and low C:N, respectively) and sonicated for 20 s. The cells were washed by centrifugation and resuspended in potassium phosphate buffer containing the two types of sonication extract. A greater extent of aggregation and higher flocculation were observed after 2–3 h incubation in the presence of sonicates from cells grown at high C:N (H-cells) compared to cells grown at low C:N. Flocculation did not occur after incubation of these cells in phosphate buffer. Boiled or proteinase K-treated sonicates originating from H-cells had lower aggregation-inducing capacity. After fractionation of the crude sonicate, both the outer-membrane protein (OMP) and the total membrane (mostly OMP) fractions possessed relatively high aggregation specific activities. The aggregation-inducing capacity of the OMP fraction strongly correlated with its protein concentration in the bioassay. Treatment of this fraction with proteinase K also decreased its aggregation-inducing activity. These findings suggest that OMPs are involved in the aggregation process of cells of A. brasilense.
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