Temperature Restriction in Entomopathogenic Bacteria.

Area of Science:

• Microbiology
• Bacterial Genetics
• Symbiotic Interactions

Background:

• Temperature is crucial for bacteria-host interactions and host switching.
• Entomopathogenic bacteria like Photorhabdus have complex life cycles, with some species causing human disease by growing at 37°C, while others are restricted to lower temperatures.

Purpose of the Study:

• To investigate the genetic basis for temperature restriction in the entomopathogenic bacterium Photorhabdus laumondii.
• To identify the specific gene(s) responsible for limiting bacterial growth at higher temperatures.

Main Methods:

• Isolation of spontaneous mutant lines of Photorhabdus laumondii capable of growth at 36-37°C.
• Whole genome sequencing of mutant lines to identify genetic alterations.
• Confirmation of gene function by restoring wild-type alleles and using transcription reporter strains.

Main Results:

• A single gene, encoding a RecG-like helicase domain protein, was identified as the primary cause of temperature restriction in most mutants.
• Mutations in this gene (Temperature Restricting Locus - TRL) were predominantly single nucleotide polymorphisms.
• The TRL operon is induced at higher temperatures (36°C), leading to bacterial replication arrest.

Conclusions:

• The Temperature Restricting Locus (TRL) system is responsible for limiting the growth temperature of Photorhabdus species.
• TRL is absent in human pathogenic Photorhabdus species, suggesting its role in host specificity.
• The TRL system may represent a fundamental mechanism for temperature restriction in diverse proteobacteria, influencing their ecological niches.