Genome size characterization of the principal endocellular symbiotic bacteria of the weevil Sitophilus oryzae, using pulsed field gel electrophoresis

The chromosome size of the principal intracellular symbiotic bacteria (endocytobiotes) of the weevil Sitophilus oryzae has been determined by pulsed held gel electrophoresis (PFGE). The restriction enzymes SpeI, SwaI and XbaI generated 22, 23 and 24 fragments, respectively. The fragment sizes ranged from 15 to 460 kb and the genome size of the symbiotic bacteria was estimated to be approximately 3.0 Mb. An additional fragment was seen when running total undigested DNA and should correspond to a plasmid of 138 kb. The principal symbiotic bacteria belong to the enterobacteriaceae family and are closely related to Escherichia coli, The difference between the genome size of E., coli (4.7 Mb) and symbiotic bacteria (3.0 Mb) was discussed and might be related to the intracellular evolution of the endocytobiotes within their host, No more than two rDNA (23S) loci were found with I-CeuI digestion, which argues against a serial fragment gene deletion in the course of evolution. (C) 1997 Elsevier Science Ltd.