Evolution of chemotactic hitchhiking

Area of Science:

• Microbial Ecology
• Evolutionary Biology
• Biophysics

Background:

• Bacteria inhabit complex environments with chemical gradients, favoring motile over non-motile cells.
• Motility is energetically expensive, necessitating optimization of swimming speed and behavior for microbial fitness.
• Cheating strategies, where slower microbes exploit faster ones, can evolve in microbial populations.

Purpose of the Study:

• To investigate the evolution of bacterial motility and cheating strategies through computational modeling.
• To analyze the impact of 'stickiness' (aggregation) on the fitness of motile and non-motile bacteria.
• To determine how chemoattractant distribution influences the parasitic or mutualistic nature of hitchhiking.

Main Methods:

• Utilized computational simulations based on physical and biological first principles.
• Modeled bacterial behavior in a controlled chemostat environment with varying chemoattractant dispersal.
• Analyzed the evolutionary dynamics of motility and sticking strategies under different environmental conditions.

Main Results:

• Stickiness enables slow-growing 'cheater' microbes to dominate when chemoattractants are at intermediate distances, leading to resource depletion.
• In scenarios with long-distance chemoattractant gradients, slow microbes initially benefit but are eventually outcompeted by faster ones.
• Fast-motile microbes preferentially aggregate, forming cooperative groups that enhance their population growth in long-distance races.

Conclusions:

• The evolution of motility and cheating is contingent upon the spatial distribution of resources.
• Hitchhiking interactions can be parasitic (cheaters exploiting others) or mutualistic (cooperative enhancement), depending on the environment.
• Microbial collective behaviors, like sticking, significantly impact population dynamics and evolutionary trajectories in heterogeneous environments.