Evidence that Lactobacillus casei insertion element ISL1 has a narrow host range

Area of Science:

• Microbiology
• Bacterial Genetics
• Molecular Biology

Background:

• The insertion element ISL1 was initially identified in Lactobacillus casei S-1.
• Understanding the distribution and host range of mobile genetic elements is crucial for bacterial evolution and adaptation.

Purpose of the Study:

• To investigate the host range and prevalence of the ISL1 insertion element.
• To determine if ISL1 is common among Lactobacillus casei strains and other related bacteria.

Main Methods:

• DNA-DNA hybridization using Southern transfers.
• A cloned internal fragment of ISL1 served as the molecular probe.
• Screening of various Lactobacillus casei strains, other Lactobacillus species, and different bacterial genera.

Main Results:

• ISL1 sequences were detected in only 3 out of 19 examined Lactobacillus casei strains.
• In two positive L. casei strains, ISL1 sequences were located on lactose plasmids.
• No homologous sequences to ISL1 were found in 14 other Lactobacillus strains or 15 strains from other bacterial genera.

Conclusions:

• The ISL1 insertion element exhibits an extremely restricted host range, primarily within specific Lactobacillus casei populations.
• ISL1's presence on lactose plasmids suggests a potential role in horizontal gene transfer within this limited host environment.