Characterization and molecular cloning of cryptic plasmids isolated from Lactobacillus casei

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Lactobacillus casei is a species with various strains, some carrying cryptic plasmids.
• Understanding plasmid diversity and function is crucial for strain improvement and genetic studies.

Purpose of the Study:

• To isolate and characterize small cryptic plasmids from Lactobacillus casei.
• To determine the genetic relationship of these plasmids with other genetic elements within L. casei.

Main Methods:

• Isolation and characterization of four small cryptic plasmids from L. casei.
• Construction of restriction endonuclease maps for each plasmid.
• Cloning of plasmids into Escherichia coli and Streptococcus sanguis using various vectors.
• DNA-DNA hybridization using labeled plasmid probes.

Main Results:

• Restriction maps were successfully constructed for three plasmids: pLZ18C (6.4 kbp), pLZ19E (4.9 kbp), and pLZ19F1 (4.8 kbp).
• Cloning into E. coli and S. sanguis was achieved, demonstrating their compatibility with different host systems.
• No significant DNA-DNA homology was found between the cryptic plasmids and large lactose plasmids or chromosomal DNA of L. casei.
• Partial homology was observed among plasmids from different L. casei strains, but not within the same strain.

Conclusions:

• The characterized cryptic plasmids are distinct genetic elements within L. casei.
• These plasmids do not appear to be directly related to lactose metabolism or the host chromosome.
• The observed partial homology suggests potential horizontal gene transfer or shared ancestry among plasmids in different strains.