Understanding microbial communities through horizontal gene transfer

Microbial communities represent the majority of biodiversity on Earth and underpin key ecosystem functions. Motivated by the experimental observation that communities from garden composts were capable of maintaining high diversity in single-carbon-source microcosms, I started by tracing the community assembly process under a serial transfer regime at a higher resolution and concluded that the diversity maintained is little affected by the complexity of the carbon source. Systematic variation of parameters in the regime demonstrated that diluting the initial inoculum has the largest effect on diversity maintained, indicative of substantial cross-feeding and functional redundancy in the microbial community. Utilising the method of inoculum dilution to manipulate diversity and a previously established design to trace community-level horizontal gene transfer (HGT) events, I proceeded to experimentally demonstrate that community-level HGT rates are positively correlated with the diversity of the communities. However, high reliance of the design on bioinformatic analyses hinders further confirmation and mechanistic studies on the HGT events detected. To overcome this, I reduced the design to a simple co-culture of a model bacterium strain, Pseudomonas fluorescens SBW25, with sterile filtrate from garden compost cultures, and successfully observed the transfer of a previously uncharacterised class of mobile genetic elements (MGEs) into SBW25. Further experiments demonstrated that the isolated MGEs enhance host fitness by providing defence against phage predators, and hijack jumbo bacteriophages for intercellular transfer. Together, this thesis reveals how diversity, HGT events and MGEs jointly modulate and are modulated by microbial community dynamics.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Christian-Albrechts-Universität zu Kiel

Year

2026

Author dc:creator

• Zhao, Yansong

Contributors dc:contributor

• Rainey, Paul B.
• Bramkamp, Marc

• Microbial Community.
• Experimental Evolution.
• Mobile Genetic Element.
• Bacteriophage Transduction.

Repository record source_url

https://macau.uni-kiel.de/receive/macau_mods_00008107

OAI identifier oai:identifier

oai:macau.uni-kiel.de:macau_mods_00008107