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Updated: Dec 25, 2025
Quantification of Interbacterial Competition using Single-Cell Fluorescence Imaging
Published on: September 2, 2021
Klebsiella pneumoniae type VI secretion system-mediated microbial competition is PhoPQ controlled and reactive oxygen
Daniel Storey1, Alan McNally2, Mia Åstrand3
1Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, Belfast, United Kingdom.
Abstract:
Klebsiella pneumoniae is recognized as an urgent threat to human health due to the increasing isolation of multidrug resistant strains. Hypervirulent strains are a major concern due to their ability to cause life-threating infections in healthy hosts. The type VI secretion system (T6SS) is widely implicated in microbial antagonism, and it mediates interactions with host eukaryotic cells in some cases. In silico search for genes orthologous to T6SS component genes and T6SS effector genes across 700 K. pneumoniae genomes shows extensive diversity in T6SS genes across the K. pneumoniae species. Temperature, oxygen tension, pH, osmolarity, iron levels, and NaCl regulate the expression of the T6SS encoded by a hypervirulent K. pneumoniae strain. Polymyxins and human defensin 3 also increase the activity of the T6SS. A screen for regulators governing T6SS uncover the correlation between the transcription of the T6SS and the ability to kill E. coli prey. Whereas H-NS represses the T6SS, PhoPQ, PmrAB, Hfq, Fur, RpoS and RpoN positively regulate the T6SS. K. pneumoniae T6SS mediates intra and inter species bacterial competition. This antagonism is only evident when the prey possesses an active T6SS. The PhoPQ two component system governs the activation of K. pneumoniae T6SS in bacterial competitions. Mechanistically, PhoQ periplasmic domain, and the acid patch within, is essential to activate K. pneumoniae T6SS. Klebsiella T6SS also mediates anti-fungal competition. We have delineated the contribution of each of the individual VgrGs in microbial competition and identified VgrG4 as a T6SS effector. The DUF2345 domain of VgrG4 is sufficient to intoxicate bacteria and yeast. ROS generation mediates the antibacterial effects of VgrG4, and the antitoxin Sel1E protects against the toxic activity of VgrG4. Our findings provide a better understanding of the regulation of the T6SS in bacterial competitions, and place ROS as an early event in microbial competition.
Insights
Klebsiella pneumoniae uses the type VI secretion system (T6SS) for bacterial and fungal competition. This system
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Klebsiella pneumoniae is a significant human pathogen, with multidrug-resistant and hypervirulent strains posing urgent threats.
- The type VI secretion system (T6SS) is crucial for microbial interactions, including antagonism and host cell engagement.
Purpose of the Study:
- To investigate the diversity and regulation of the T6SS in K. pneumoniae.
- To understand the role of T6SS in inter- and intra-species competition and its effectors.
Main Methods:
- In silico analysis of T6SS genes across 700 K. pneumoniae genomes.
- Experimental screening of regulators and environmental factors affecting T6SS expression.
- Identification and characterization of T6SS effectors, including VgrG4.
Main Results:
- Extensive diversity in T6SS genes was observed across K. pneumoniae strains.
- TSS expression is regulated by environmental factors (temperature, pH, etc.) and specific regulators (PhoPQ, H-NS, etc.).
- K. pneumoniae T6SS mediates bacterial and fungal antagonism, with VgrG4 identified as a key effector causing ROS-mediated toxicity.
Conclusions:
- The PhoPQ two-component system is essential for T6SS activation in bacterial competition.
- VgrG4 effector, through ROS generation, plays a critical role in K. pneumoniae's competitive fitness.
- This study enhances understanding of T6SS regulation and its role in microbial warfare.
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