Cytoplasmic contractile injection systems mediate cell death in Streptomyces

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• Contractile injection systems (CIS) are bacteriophage-like structures involved in bacterial interactions.
• CIS gene clusters in Gram-positive bacteria are understudied.
• Streptomyces coelicolor is a model organism for studying Gram-positive multicellular bacteria.

Purpose of the Study:

• To characterize the CIS in Streptomyces coelicolor (CIS^Sc).
• To investigate the function of CIS^Sc in cellular development and stress response.
• To elucidate the structural and functional mechanisms of CIS^Sc.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for structural analysis.
• Cryo-electron tomography (cryo-ET) to study contraction.
• Fluorescence light microscopy to observe cell death and development.
• Genetic manipulation to create CIS^Sc mutants.

Main Results:

• CIS^Sc are intracellular, expressed in vegetative hyphae, and mediate cell death upon stress.
• CIS^Sc contraction is linked to reduced cellular integrity.
• Absence of functional CIS^Sc affects hyphal differentiation and secondary metabolite production.
• Three effector proteins were identified that influence CIS^Sc function.

Conclusions:

• CIS^Sc play a novel intracellular role in Gram-positive bacteria, mediating regulated cell death.
• CIS^Sc are involved in regulating the life cycle and development of multicellular bacteria.
• This work provides a framework for studying CIS functions in Gram-positive organisms.