A Sensory Pathway Controls Motile Microcolony Formation and Spatial Organization in Gliding Bacteria

Area of Science:

• Microbiology
• Cell Biology
• Biochemistry

Background:

• Understanding bacterial multicellularity is crucial for fields like medicine and biotechnology.
• Motile bacteria navigate surfaces, but the mechanisms converting environmental signals into collective behaviors are unclear.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the transition of motile bacteria from dispersed states to cohesive multicellular assemblies.
• To identify key regulators involved in bacterial collective behaviors and microcolony formation.

Main Methods:

• Genetic analysis of *Flavobacterium johnsoniae* using point mutations and suppressor mutations in the RgzA protein.
• Transcriptomic analysis to identify genes regulated by RgzA and RgzB.
• Perturbation studies to investigate the role of iron availability.
• Microscopy to observe bacterial behavior and microcolony formation (zorbs).

Main Results:

• A sensory kinase, RgzA, was identified as a key driver of zorb formation in *F. johnsoniae*.
• Mutations in RgzA promoted zorb formation and biofilm development while suppressing swarming.
• The response regulator RgzB forms a signaling circuit with RgzA, regulating zorbing.
• Iron availability was linked to the transition, with RgzAB signaling mediating cohesive, motile microcolony formation.
• Co-zorbs formed in mixed populations, encapsulating wild-type cells and creating connected cellular networks.

Conclusions:

• Sensory signaling, particularly involving RgzA and RgzB, governs the formation and spatial organization of motile multicellular bacterial assemblies.
• This study establishes a link between sensory transduction and collective organization states, shifting bacterial behavior from swarming to zorb-based exploration.
• The findings provide insights into how bacteria transition between different collective behaviors in response to environmental cues.