SEQUENCE POLYMORPHISM IN THE BETA-TUBULIN GENE REVEALS HETEROGENEOUS AND VARIABLE POPULATION STRUCTURES IN CRYPTOSPORIDIUM-PARVUM

Restriction fragment length polymorphism (RFLP) analysis of isolates o f Cryptosporidium parvum has revealed two subgroups, termed H and C, T he limited resolution of the RFLP method precludes an in-depth study o f the genetic structure of C. parvum populations. Published C, parvum restriction polymorphisms lie within protein-coding regions known to b e more homogeneous than noncoding sequences. To better assess the degr ees of heterogeneity between and within C, parvum isolates, sequence p olymorphism in the beta-tubulin intron, the only C, parvum intron desc ribed to date, was investigated. In contrast to the two genotypes dist inguished by multilocus RFLP, several alleles were detected by sequenc e and RFLP analysis of the beta-tubulin intron and adjacent exon 2, Is olates carrying different beta-tubulin alleles were found. Significant ly, one of the beta-tubulin alleles present in two geographically unre lated isolates combined features of C- and II-type isolates, suggestin g that it might have arisen from a recombination event. A comparison o f multiple samples of a calf-propagated laboratory isolate showed that the ratio of different beta-tubulin alleles fluctuated during serial passage.