%0 Journal Article %A Burdman, Saul %A Jurkevitch, Edouard %A Schwartsburd, Boris %A Okon, Yaacov %T Involvement of outer-membrane proteins in the aggregation of Azospirillum brasilense %D 1999 %J Microbiology, %V 145 %N 5 %P 1145-1152 %@ 1465-2080 %R https://doi.org/10.1099/13500872-145-5-1145 %K flocculation %K outer-membrane proteins %K aggregation %K Azospirillum brasilense %I Microbiology Society, %X 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. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/13500872-145-5-1145