CLOUD ACTIVATION CHARACTERISTICS OF AIRBORNE ERWINIA-CAROTOVORA CELLS

Several strains of plant pathogenic bacteria, Erwinia carotovora carot ovora and E. carotovora atroseptica, were observed to be active as clo ud condensation nuclei (CCN). The CCN supersaturation spectra of bacte rial aerosols were measured in the laboratory and compared to the acti vity of ammonium sulfate. Approximately 25%-30% of the aerosolized bac terial cells activated droplets at 1% water supersaturation compared t o 80% activation of the ammonium sulfate aerosol. Physical and numeric al simulations of cloud droplet activation and growth on bacteria were also performed. Both simulations predict that aerosolized bacteria wi ll be incorporated into cloud droplets during cloud formation. Results strongly support the hypothesis that significant numbers of the teste d bacterial strains are actively involved in atmospheric cloud formati on and precipitation processes following natural aerosolization and ve rtical transport to cloud levels.