High molecular mass agarose matrix supports growth of bloodstream forms of pleomorphic Trypanosoma brucei strains in axenic culture.

Primary axenic culture of Trypanosoma brucei bloodstream forms almost invariably requires a period of culture adaptation with cell death and clonal selection. This has been particularly difficult and in many cases unsuccessful for natural pleomorphic strains, which are characterized by their ability to differentiate from replicating long slender bloodstream forms into short stumpy forms. Here we show that a representative set of pleomorphic T. brucei strains can be cultured in vitro on agarose plates without any previous adaptation period and selection. The slender morphology was retained and the growth rate was identical to the growth rate in vivo. Long term in vitro culture for 3 months with this method did not affect the ability of the AnTat 1.1 strain to give rise to pleomorphic infections in mice. Stumpy populations emanating from these infections transformed rapidly and synchronously into dividing procyclic forms when triggered with cis-aconitate and a temperature shift. The growth supporting activity of agarose plates could be traced to high molecular mass polymeric agarose; beta-agarase digestion destroyed the activity. Membrane chamber experiments show that direct physical contact of trypanosomes with the agarose matrix is essential. In the absence of high molecular mass agarose, the cell division process is grossly impaired. We suggest that agarose mimics an interaction of trypanosomes with the host's extracellular matrix. Applications of the culture method are discussed.