TRANSFORMATION OF MONOMORPHIC TRYPANOSOMA-BRUCEI BLOOD-STREAM FORM TRYPOMASTIGOTES INTO PROCYCLIC FORMS AT 37-DEGREES-C BY REMOVING GLUCOSEFROM THE CULTURE-MEDIUM

African trypanosomes have been shown previously to undergo efficient t ransformation from bloodstream forms to procyclic (insect dwelling) fo rms in vitro by adding citrate and/or cis-aconitate to the culture med ium and lowering incubation temperature to 27 degrees C. In this paper , it is shown that strain 427 monomorphic bloodstream forms of Trypano soma brucei grown in axenic culture at 37 degrees C can be transformed to procyclic forms by simply replacing the glucose carbon source in t he culture medium with glycerol. The removal of glucose from the mediu m results in the loss of the variant surface glycoprotein, the acquisi tion of cell surface procyclic acidic repetitive protein, the synthesi s of procyclic-specific glycosylphosphatidylinositol precursors and th e acquisition of substantial resistance to salicyl hydroxamic acid and glycerol within 72 h. A procyclic-specific cytoskeletal protein, know n to be a marker of the late stage of transformation, is fully express ed by 96 h but full trans-sialidase activity appears only after 18-30 days. The transformation process described here is slower and less eff icient than that previously described for monomorphic trypanosomes, us ing citrate and/or cis-aconitate and temperature shift as triggers. Ho wever, the separation of the transformation process from these stimuli is significant and the effects of glucose deprivation described here may reflect some of the events that occur in vivo in the tsetse fly mi dgut, where glucose levels are known to be very low. (C) 1998 Elsevier Science B.V. All rights reserved.