Lactococcus lactis AbiD1 abortive infection efficiency is drastically increased by a phage protein

Area of Science:

• Bacteriophage-bacteria interactions
• Molecular biology of bacterial defense mechanisms

Background:

• Lactococcus lactis employs abortive infection mechanisms, such as AbiD1, to prevent phage propagation.
• Phage bIL66 sensitivity to AbiD1 was previously linked to a four-gene operon expressed during the phage's middle development stage.

Purpose of the Study:

• To identify the specific phage gene responsible for bIL66 sensitivity to the AbiD1 abortive infection system.
• To elucidate the role of the identified gene product in the interaction between phage bIL66 and the AbiD1 mechanism.

Main Methods:

• Isolation and characterization of spontaneous bIL66 mutants resistant to AbiD1.
• Genetic analysis to pinpoint the mutation responsible for AbiD1 resistance.
• In trans complementation experiments involving the overproduction of wild-type and mutant Orf1 proteins.

Main Results:

• Spontaneous mutants resistant to AbiD1 were obtained, revealing that the phage orf1 gene product determines sensitivity.
• Overexpression of wild-type Orf1 in AbiD1-carrying cells enhanced the efficiency of the AbiD1 system against both wild-type and mutant phages.
• Overexpression of a mutant Orf1 did not confer the same enhancement, indicating the functional importance of specific Orf1 domains.

Conclusions:

• The Orf1 protein is the key determinant of phage bIL66 sensitivity to the Lactococcus lactis AbiD1 abortive infection mechanism.
• Wild-type Orf1 likely activates AbiD1 expression or activity, thereby increasing the defense efficacy against phage infection.