Mutagenesis via IS transposition in Deinococcus radiodurans.

Area of Science:

• Microbiology
• Genetics
• Genomics

Background:

• Insertion sequences (ISs) are mobile genetic elements found in many bacterial genomes.
• Deinococcus radiodurans is known for its exceptional radioresistance, suggesting unique DNA repair mechanisms.
• The role of IS elements and their activity under DNA-damaging conditions in D. radiodurans is not fully understood.

Purpose of the Study:

• To investigate the abundance and activity of insertion sequences (ISs) in Deinococcus radiodurans.
• To determine the impact of DNA damage, specifically gamma-ray and UV irradiation, on IS transposition.
• To analyze the contribution of IS insertions to spontaneous and induced mutations.

Main Methods:

• Forward mutagenesis assay to detect inactivation events.
• Analysis of trimethoprim-resistance (Tmp(R)) and rifampicin-resistance (Rif(R)) mutations.
• BLASTN for identifying Miniature Inverted-repeat Transposable Element (MITE) genomic copies.
• Exposure of D. radiodurans to gamma-ray and UV irradiation.

Main Results:

• 75% of spontaneous trimethoprim-resistance mutations resulted from IS insertion into the thyA gene.
• Five different ISs were found to be transpositionally active.
• Gamma-ray irradiation (10 kGy) increased Tmp(R) mutant frequency 10-fold and ISDra2 transposition 100-fold.
• UV irradiation (600 J m-2) induced ISDra2 transposition 50-fold.
• Gamma-irradiation induced Rif(R) point mutations, reaching a 16-fold increase at 2 kGy.

Conclusions:

• IS elements are highly active in D. radiodurans, contributing significantly to genetic variation.
• DNA damage strongly induces IS transposition and point mutations, enhancing genetic variability.
• This increased variability may have long-term evolutionary consequences for D. radiodurans' fitness in its habitat.