Ultrastructural Aspects of Host-parasite Relationships Between Xanthomonas oryzae and Bdellovibrio Isolates

Abstract

Host-parasite relationships between an isolate of Xanthomonas oryzae, N5874, and two isolates of Bdellovibrio, BdN6801 and BdN6802, were studied by using ultrathin sectioning and electron microscopy.
With the combination of X. oryzae N5874 and BdN6801, the parasitic process was made clear as follows. Disorganization in the cytoplasm and nuclear area of the host cell was observed from early stage of the attachment of Bdellovibrio. The host components became granular and unevenly distributed, and the host cell changed into spheroplast. A penetration pore was made on the host cell wall at the site of attachment, and the parasite invaded smoothly into the intraperiplasmic space of the host cell. The granulated cytoplasm in spheroplast disappeared gradually to become ghost afterwards with elongation of the parasite. The cytoplasmic membrane of the host, however, remained almost intact till later stage of the latent period. The elongated parasite split into several cells prior to the disruption of host cell wall.
When BdN6802 attacked X. oryzae N5874, parasitic process was almost the same as in the case of BdN6801 with a few exceptions in some aspects at the site of attachment and penetration. BdN6802 attached to the host cell swelled at anterior tip and the mesosome existing there was often observed. On the occasion of the penetration of BdN6802, the parasite was constricted by X. oryzae cell wall at the marginal part of the penetration pore. The constriction appeared probably due to the rigidity of the host cell wall and insufficient pore size for penetration.