DFG-Project MultiTip

Summary

Despite a long-standing view of bacteria as simple unicellular organisms, members of the Hyphomicrobiaceae family challenge this paradigm through their remarkable morphological complexity and facultative multicellularity. The well-known representative Rhodomicrobium vannielii, in particular, exhibits an intricate life cycle that includes tip-growing hyphae, branching morphogenesis, asymmetric budding, and the formation of tissue-like multicellular arrays - traits that blur the boundaries between prokaryotic and eukaryotic cellular organization. However, the molecular mechanisms underlying these processes remain largely unknown, due to historical limitations in genetic tools and model systems for this group.

This proposal aims to harness R. vannielii as a genetically tractable model for studying bacterial morphogenesis and multicellularity. Building on our development of the first comprehensive genetic toolkit for R. vannielii, as well as our discovery of key roles for bactofilins in hyphal tip growth, we now seek to systematically dissect the molecular determinants that drive polar growth, chromosome segregation through extended hyphae, and the transition to multicellular organization.

The project is structured around three major objectives:

(1) identify and characterize the protein machinery that governs apical growth, with a focus on Rgs-family proteins and their interactions with bactofilins and peptidoglycan-processing enzymes;

(2) elucidate the coordination between growth pole establishment and chromosome segregation, particularly the roles of polar landmark proteins like PopZ and the ParABS system; and

(3) uncover the genetic basis of multicellularity by performing genome-wide transposon mutagenesis to identify regulators that control the switch between unicellular and multicellular life cycles.

Using an integrative combination of live-cell fluorescence microscopy, super-resolution imaging, genetic manipulation, and interaction assays, we aim to map the dynamic spatial organization of growth and division machinery at high resolution. Our preliminary data reveal unexpected features, such as polar growth uncoupled from septation, potential cytoplasmic communication through hyphal septa, and active chromosome transport through narrow, branching hyphae - each representing a departure from textbook bacterial cell biology.

By establishing R. vannielii as a model system, this project will not only provide fundamental insights into how bacteria can develop complex multicellular structures but also shed light on the evolution of morphological diversity and cellular specialization in prokaryotes.

Principal Investigator: Dr. Frank-Dietrich Müller