Altruism and cooperation in plasmids: an initial experimental approach

The existence of altruistic behavior, and the intricate mechanisms that allow the fixation of cooperation within populations constitute a mystery that has been unanswered since the birth of evolutionary biology. In this context, multilevel selection arises as one of the theoretical frameworks for the evolution of cooperation. This phenomenon, which introduces the idea that competition not only transpires at the individual level, but also between groups, has been described analytically in simple biological instances such as the replication control genes of bacterial plasmids. In this system, plasmids encounter competition at the individual level, inside their host, and at the group level, which corresponds to competition between bacteria. In this way, plasmid that consistently experience replication compared to their cellular counterparts are more likely to dominate in descendant cells. However, bacteria with such overreplicated plasmids generally face a reduced likelihood of fixating in the overall population. With this in mind, Johan Paulsson in his article Multilevel Selection on Plasmid Replication describes which conditions need to be met so that altruist individuals have a higher chance of establishing in the bacterial population. However, no experimental confirmation of this expression has been carried out. Hence, this project is the first step towards completing the task of reproducing and studying multilevel selection in this biological system. This endeavor consists on executing long term evolution experiments (LTEE) but while maintaining a fairly constant population of bacteria. This is why they need to be carried out in a turbidostat, a machine that automatizes the process of dilution of the bacterial sample based on turbidity data. Thus, this project focuses in the development and documentation of a comprehensive guide for utilizing and maintaining the turbidostat. The guide encompasses a rebuilding process and protocols for tube system changes, tube sterilization, media changes, pump speed measurements, machine calibration, and ideal dilution time calculations. Furthermore, a dynamic model for bacterial growth within the machine was developed, in order to facilitate accurate LTEE simulations. Extensive experimental data from several trial runs are used to characterize growth curve behaviors, including biofilm formation instances. Additionally, initial findings from LTEE experiments done in the machine suggest changes in bacterial duplication times, indicative of adaptation. However, further experiments are required for confirmation. Finally, the results obtained enhances the understanding of the machine operational principles, and exhibit the turbidostat's mechanical reliability for its use in LTEEs.

• Autores: Hernández, Juan Sebastián
• Tipo de recurso: Trabajo de grado de pregrado
• Fecha de publicación: 2024
• Institución: Universidad de los Andes
• Repositorio: Séneca: repositorio Uniandes
• Idioma: eng
• OAI Identifier: oai:repositorio.uniandes.edu.co:1992/73880
• Acceso en línea: https://hdl.handle.net/1992/73880
• Palabra clave: Biología de sistemas; Biología evolutiva; Cooperación; Experimentos de evolución a largo plazo; Biofilm; Biología; Microbiología
• Rights: openAccess
• License: Attribution-NonCommercial-NoDerivatives 4.0 International