The Erwinia chrysanthemi type III secretion system is required for multicellular behavior

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Cellular Biology

Background:

• Enterobacterial pathogens display aggregative multicellular behavior, forming pellicles and biofilms.
• Pellicle formation necessitates extracellular polysaccharide, cellulose, and protein filaments like curli.
• Protein filaments similar to curli can be produced by various secretion systems, including the type III secretion system (TTSS).

Purpose of the Study:

• To investigate the role of the TTSS in pellicle formation in Erwinia chrysanthemi, a bacterium lacking curli genes.
• To elucidate the genetic requirements for TTSS-mediated pellicle formation.
• To assess the utility of pellicle formation as a high-throughput screening method for TTSS mutants or inhibitors.

Main Methods:

• Utilized pellicle formation assays to study aggregative multicellular behavior in Erwinia chrysanthemi.
• Investigated the genetic regulation of TTSS in pellicle formation, focusing on hrpY, hrpS, and hrpL homologs.
• Examined the temperature dependence of pellicle formation and the role of cellulose.

Main Results:

• Erwinia chrysanthemi requires the TTSS, not curli, for pellicle formation, supporting a model of generic protein filaments in aggregative behavior.
• The hrpY, hrpS, and hrpL genes are crucial for TTSS activity and subsequent pellicle formation.
• Pellicle formation is temperature-dependent, with no formation at 36°C despite TTSS gene expression. Cellulose is a component, but not strictly required.

Conclusions:

• The TTSS plays a critical role in enterobacterial pellicle formation, substituting for curli in some species.
• The identified genetic pathway (hrpY-hrpS-hrpL) is essential for TTSS-mediated pellicle development.
• Pellicle formation assays offer a valuable, cost-effective method for screening TTSS-related mutants and inhibitors.