Genome size and genetic map of Cowdria ruminantium

Onderstepoort Veterinary Institute, Onderstepoort, 0110, Republic of South Africa 1 Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164, USA 2 Author for correspondence: E. P. de Villiers. Tel: +31 30 253 6923. Fax: +31 30 254 0784. e-mail: e.devilliers{at}vet.uu.nl Cowdria ruminantium is the cause of a serious tick-borne disease of domestic ruminants, known as heartwater or cowdriosis. The organism belongs to the tribe Ehrlichieae , which contains obligate intracellular pathogens, causing several important animal and human diseases. Although a few C. ruminantium genes have been cloned and sequenced, very little is known about the size, gross structure and organization of the genome. This paper presents a complete physical map and a preliminary genetic map for C. ruminantium . Chromosomal C. ruminantium DNA was examined by PFGE and Southern hybridization. PFGE analysis revealed that C. ruminantium has a circular chromosome approximately 1576 kb in size. A physical map was derived by combining the results of PFGE analysis of DNA fragments resulting from digestion of the whole genome with Ksp I, Rsr II and Sma I and Southern hybridization analysis with a series of gene probes and isolated macrorestriction fragments. A genetic map for C. ruminantium with a mean resolution of 290 kb was established, the first for a member of the Ehrlichieae . A total of nine genes or cloned C. ruminantium DNA fragments were mapped to specific Ksp I, Rsr II and Sma I fragments, including the major antigenic protein gene, map-1. Keywords: Cowdria ruminantium , Rickettsiales , genome size, genetic map Abbreviations: MACS, magnetic cell separation a Present address: Division of Parasitology and Tropical Veterinary Medicine, Faculty of Veterinary Medicine, Utrecht University, PO Box 80.165, 3508 TD Utrecht, The Netherlands.