WIDE VARIATION IN DNA CONTENT AMONG ISOLATES OF TRYPANOSOMA-BRUCEI SSP

The DNA contents of 18 Trypanosoma brucei ssp. stocks were compared us ing flow cytometry, karyotype analysis and quantitation of repetitive DNA by Southern blotting and hybridisation. The DNA contents of Type I T. b. gambiense stocks were lower than those of non-gambiense stocks, bur both groups showed a wide range of variation in DNA content. Amon gst T. b. gambiense stocks, Mabia at the lower end of the range had 14 % less DNA than Dal 972 at the top of the range. Similarly, amongst no n-gambiense stocks, 117R at the lower end of the range had 14% less DN A than LM55 at the top of the range. The T. b. gambiense stock Mabia h ad 29% less DKA than non-gambiense stock LM55. The DNA content of Type II T. b, gambiense clearly fell within the non-gambiense range. Karyo type analysis showed that all T. b. gambiense stocks had minichromosom es, albeit fewer than non-gambiense stocks. This result was verified b y hybridisation with probes for satellite DNA and a telomere-specific repeat. Hybridisation with a probe for the beta-tubulin genes also rev ealed an apparent reduction of gene copy number in T. b. gambiense rel ative to non-gambiense stocks. In conclusion, there is a wide range of variation in genome size in T. brucei ssp., with T. b. gambiense stoc ks at the lower end of the range. The reduction in genome size correla tes with loss of repeated genes and non-coding sequences in T. b.gambi ense stocks. and is not confined to chromosomes of a particular size. Copyright (C) 1997 Elsevier Science B.V.