Bacterial Adaptation by a Transposition Burst of an Invading IS Element

Area of Science:

• Microbial Evolution
• Genomics
• Molecular Biology

Background:

• The role of transposable elements (TEs) in adaptive evolution is not fully understood, particularly in non-model organisms.
• Acaryochloris marina strain CCMEE 5410 exhibits recent or ongoing insertion sequence (IS) element expansion and high transposase gene content.

Purpose of the Study:

• To investigate if IS elements are a primary source of beneficial mutations during laboratory evolution of Acaryochloris marina.
• To understand the contribution of ISAm1, a recently invaded IS element, to adaptive evolution.

Main Methods:

• Laboratory evolution experiment over 400 generations with eight independent populations of Acaryochloris marina.
• Mutation detection and analysis, focusing on IS transposition events.
• Assessment of fitness effects of ISAm1-induced mutations under varying carbon availability.

Main Results:

• Most detected mutations were IS transposition events, predominantly driven by the copy-and-paste activity of ISAm1.
• ISAm1 transposition was responsible for repeatable evolutionary dynamics and mutations in inorganic carbon acquisition genes.
• ISAm1-associated mutations increased growth rate under low carbon conditions, but not under high carbon availability.

Conclusions:

• A single IS element's activity can significantly fuel adaptation over hundreds of generations.
• ISAm1's activity is a major driver of adaptation in Acaryochloris marina, particularly for carbon acquisition.
• While driving adaptation, extensive IS activity may also limit evolutionary rates via clonal interference.