Molecular Cloning and Deoxyribonucleic Acid Polymorphisms in Lactobacillus acidophilus and Lactobacillus gasseri

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Abstract
Lactobacillus strain ADH is a bile-resistant, bacteriocin-producing human isolate that was phenotypically classified within the Lactobacillus acidophilus group. Total DNA and phage DNA extracted from strain ADH were separately digested with BclI and ligated with BclI-digested pGK12. Following electroporation of these ligation mixtures directly into strain ADH, electrotransformants were recovered at frequencies of 1.5 x 10(3) and 2.0 x 10(4)/micrograms of pGK12 for preparations of pGK12::phage DNA and pGK12::total DNA, respectively. Among the electrotransformants screened, 6 and 22% contained passenger DNA of either phage DNA or chromosomal origin, respectively, as determined by restriction-enzyme analyses and hybridization assays. Derivatives of pGK12 containing passenger DNA of chromosomal (pTRK120) or phage (pTRK121) origin and pTRK15 (native cryptic plasmid) were evaluated for use as species-specific probes. The strain ADH-derived probes hybridized primarily to members of the B-1 and B-2 lactobacilli homology groups and demonstrated strain-specific polymorphisms within these groups. Identical hybridization patterns were established for strain ADH and Lactobacillus gasseri VPI 6033 (ATCC 19992). Identification of DNA probes and establishment of a host-vector cloning system have facilitated our efforts to characterize the Lactobacillus chromosome and to distinguish between closely related species thought to be important inhabitants of the gastrointestinal tract.