ISL1: a new transposable element in Lactobacillus casei

Area of Science:

• Microbiology
• Molecular Biology
• Genomics

Background:

• Temperate Lactobacillus phages are crucial for understanding bacterial genetics and phage-bacterium interactions.
• Virulent mutants of phages can provide insights into genetic changes driving host range and pathogenicity.

Purpose of the Study:

• To elucidate the genome structures of the temperate Lactobacillus phage phi FSW and its virulent mutants, phi FSVs.
• To identify and characterize genetic elements responsible for the differences between the temperate phage and its virulent mutants.

Main Methods:

• Restriction enzyme analysis of phage DNA.
• Heteroduplex analysis to compare DNA structures.
• Nucleotide sequence analysis to determine precise genetic makeup.

Main Results:

• Two of three virulent phi FSV mutants contained a 1.3 kbp insertion, designated ISL1, at varying locations within the phi FSW genome.
• ISL1 is 1,256 bp long, featuring two significant open reading frames and terminal inverted repeats.
• ISL1 was flanked by 3 bp direct repeats of the host phi FSW sequence, indicating its insertion mechanism.

Conclusions:

• The ISL1 element exhibits key characteristics of a transposable element.
• ISL1 is identified as a mobile genetic element within the Lactobacillus casei phage system.
• The insertion of ISL1 likely contributes to the genetic variation observed in the virulent phage mutants.