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Etiology

Stable L-Phase of Erwinia carotovora Induced by Ultraviolet Irradiation. E. Cabezas de Herrera, Institute of Microbiology "Jaime Ferrán", Consejo Superior de Investigaciones Cientificas, Madrid, Spain; M. Rubio Huertos(2), and O. Garcia Jurado(3). (2)(3)Institute of Microbiology "Jaime Ferrán", Consejo Superior de Investigaciones Cientificas, Madrid, Spain. Phytopathology 66:400-405. Accepted for publication 31 October 1975. DOI: 10.1094/Phyto-66-400.

After having obtained the lethality curve of Erwinia carotovora strain 2012 and established the sensitivity of the bacteria to ultraviolet radiation, we found that the minimal sublethal dose of 15 seconds (105 erg/mm²/sec) was the most suitable. We obtained typical L-phase colonies on agar-serum plates by irradiating the bacteria with that dose when the DNA was in the open-strand state. The colonies were formed by spherical elements with two well differentiated layers: an outer degraded layer and the inner or cytoplasmic membrane. These spheroplasts are less pathogenic than the parental bacteria on Phaseolus vulgaris and Vicia faba. These forms have been transferred weekly during five years without reversal to the normal bacillary form and they still show the same characteristics. Ten per cent horse serum is necessary for the development of the L-forms, but they are not induced by it.