Lytic/Lysogenic Transition as a Life-History Switch.

Area of Science:

• Microbiology
• Virology
• Theoretical Ecology

Background:

• Temperate viruses exhibit lytic (active replication) and lysogenic (dormant integration) life cycles.
• The transition between these cycles is crucial for viral survival and ecological dynamics.
• Understanding this transition is key to comprehending virus-bacteria interactions.

Purpose of the Study:

• To develop an optimal life-history model explaining the transition between viral lytic and lysogenic cycles.
• To introduce and define the 'fitness switch' as the determinant of this transition.
• To predict viral ecological behavior and interactions based on the model.

Main Methods:

• A discrete-time model of phage/bacteria population dynamics was formulated.
• Infection dynamics were modeled using Poisson sampling of virions.
• The model incorporates density-dependent viral absorption and defines the 'fitness switch' criterion.

Main Results:

• The 'fitness switch' occurs when viral population growth is faster as prophage (lysogenic) than as virions (lytic), or vice versa.
• A 'prophage lock' mechanism explains how beneficial prophages become permanently integrated.
• The model qualitatively predicts that environmental enrichment increases lysogeny and fluctuating conditions promote horizontal gene transfer.

Conclusions:

• The 'fitness switch' model provides a framework for understanding temperate virus life-history transitions.
• The model's predictions align with the 'Piggyback-the-Winner' hypothesis in virus ecology.
• Prophage integration can lead to tripartite holobiont formation, impacting host microbiomes.