Endosymbiosis of ß-Proteobacteria with trypanosomatid
protozoa: Genetic rescue of host defects in heme biosynthesis
pathway
Ito, H.1, Lu, H.-G.1, Yadava, N.1, Sassa, S.2, Chang, K.-P.1
1Department of Microbiology/Immunology, Chicago Medical School,
3333 Green Bay Rd., North Chicago, IL 60064, USA;
2Rockefeller University, New York, NY 10021
Endosymbionts exist in some trypanosomatid protozoa. Earlier, we described the symbionts of Crithidia as bacteria beneficial to their hosts. Genetic distance analysis of ssu-rDNA sequences suggests that the crithidial symbionts belong to the ß-Proteobacteria; and that they originate monophyletically and co- evolve with their hosts [1]. The endosymbionts rectify certain biosynthetic deficiencies of Crithidia, for example, missing of the porphobilinogen deaminase (PBGD) [2] in the heme biosynthesis pathway. The incompleteness of this pathway renders all trypanosomatid protozoa nutritionally dependent on the exogenous hemin for growth. A rat PBGD cDNA was cloned into p6.5 - a vector constructed for Leishmania [4,5]. These trypanosomatids depend in part on the heme synthesized by their host cells [3]. Leishmania were transfected with p6.5/PBGD. Western and Northern blot analyses of the transfectants verified the expression of PBGD in those with the correctly oriented gene. Significantly, the expressed PBGD is enzymatically active, giving high specific activities. In chemically defined medium, all transfectants still require hemin for growth. The defects of trypanosomatid protozoa in heme biosynthesis thus may not be limited to PBGD. Work is under way to assess additional deficiencies for genetic complementation.
[1] Du, Y et al. (1994) Proc Nat Acad Sci USA 91, 8337-41
[2] Chang, K-P et al. (1975) Proc Nat Acad Sci USA 72, 2979-83
[3] Chang, CS & Chang, K-P (1985) Mol Biochem Parasit 16, 267-76
[4] Liu, X & Chang, K-P (1992) Mol Cell Biol 12, 4112-22
[5] Kawazu, S-I et al. (1997) Gene 196, 49-59.
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Wednesday, April 8 |
09:25 am |