Genome size and genetic map of Cowdria ruminantium

Cowdria ruminantium is the cause of a serious tick-borne disease of domesti c ruminants, known as heartwater or cowdriosis. The organism belongs to the tribe Ehrlichieae, which contains obligate intracellular pathogens, causin g several important animal and human diseases. Although a few C. ruminantiu m genes have been cloned and sequenced, very little is known about the size , gross structure and organization of the genome. This paper presents a com plete physical map and a preliminary genetic map for C. ruminantium. Chromo somal C. ruminantium DNA was examined by PFGE and Southern hybridization. P FGE analysis revealed that C. ruminantium has a circular chromosome approxi mately 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 ge nome with KspI, RsrII and SmaI and Southern hybridization analysis with a s eries of gene probes and isolated macrorestriction fragments. A genetic map for C. ruminantium with a mean resolution of 290 kb was established, the f irst for a member of the Ehrlichieae. A total of nine genes or cloned C. ru minantium DNA fragments were mapped to specific KspI, RsrII and SmaI fragme nts, including the major antigenic protein gene, map-1.