Genotyping based on variable-number tandem repeats (VNTR) is currently a very promising tool for studying the molecular epidemiology and phylogeny of Mycobacterium tuberculosis. Here we investigate the polymorphisms of 48 loci of direct or tandem repeats in M. tuberculosis previously identified by our group. Thirty-nine loci, including nine novel ones, were polymorphic. Ten VNTR loci had high allelic diversity (Nei's diversity indices > 0.6) and subsequently were used as the representative VNTR typing set for comparison to IS6110-based restriction fragment length polymorphism (RFLP) typing. The 10-locus VNTR set, potentially providing >2 ؋ 10 9 allele combinations, obviously showed discriminating capacity over the IS6110 RFLP method for M. tuberculosis isolates with fewer than six IS6110-hybridized bands, whereas it had a slightly better resolution than IS6110 RFLP for the isolates having more than five IS6110-hybridized bands. Allelic diversity of many VNTR loci varied in each IS6110 RFLP type. Genetic relationships inferred from the 10-VNTR set supported the notion that M. tuberculosis may have evolved from two different lineages (high and low IS6110 copy number). In addition, we found that the lengths of many VNTR loci had statistically significant relationships to each other. These relationships could cause a restriction of the VNTR typing discriminating capability to some extent. Our results suggest that VNTR-PCR typing is practically useful for application to molecular epidemiological and phylogenetic studies of M. tuberculosis. The discriminating power of the VNTR typing system can still be enhanced by the supplementation of more VNTR loci.Over a decade, the fingerprinting method based on restriction fragment length polymorphism (RFLP) of IS6110 insertion sequences has been established as the standard for typing strains of Mycobacterium tuberculosis. IS6110 RFLP fingerprinting is very powerful when it is used to classify M. tuberculosis isolates harboring a large number of IS6110 in their chromosomes (33). However, the prevalence of M. tuberculosis strains harboring no, single, or few copies of IS6110 in their chromosomes dramatically lowers the discriminating efficiency of the method (1). In this regard, many alternative RFLPbased fingerprinting methods, e.g., direct repeat (DR) and polymorphic GC-rich repetitive sequence RFLP fingerprinting, are supplementarily used for differentiation (10, 24). In addition, various methods based on PCR, for example, ligation-mediated PCR, mixed-linker PCR, double repetitive element PCR, and DR-based spoligotyping, were developed mainly in order to avoid the technical demand of RFLP (5, 11, 14, 21). However, most PCR-based methods displayed poor discrimination power compared to the standard IS6110 RFLP typing, whereas others were critically confronted with limitations with respect to reproducibility and reliability (16).Variable-number tandem repeats (VNTR), often referred to as micro-or minisatellite DNA, are ubiquitous in eukaryotes and humans. They have been extensiv...

Five microorganisms, three bacteria and two yeasts, capable of degrading Tapis light crude oil were isolated from oil-contaminated soil in Bangkok, Thailand. Soil enrichment culture was done by inoculating the soil in mineral salt medium with 0.5% v/v Tapis crude oil as the sole carbon source. Crude oil biodegradation was measured by gas chromatography method. Five strains of pure microorganisms with petroleum degrading ability were isolated: three were bacteria and the other two were yeasts. Candida tropicalis strains 7Y and 15Y were identified as efficient oil degraders. Strain 15Y was more efficient, it was able to reduce 87.3% of the total petroleum or 99.6% of n-alkanes within the 7-day incubation period at room temperature of 25 +/- 2 degrees C.