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Updated: Feb 15, 2026
Quantification of Interbacterial Competition using Single-Cell Fluorescence Imaging
Published on: September 2, 2021
Mutations in Two Paraburkholderia phymatum Type VI Secretion Systems Cause Reduced Fitness in Interbacterial
Samanta Bolzan de Campos1, Martina Lardi1, Alessia Gandolfi1
1Institute of Plant and Microbial Biology, University of Zurich, Zurich, Switzerland.
Abstract:
Paraburkholderia phymatum is a highly effective microsymbiont of Mimosa spp. and has also been shown to nodulate papilionoid legumes. P. phymatum was found to be highly competitive both in a natural environment as well as under controlled test conditions and is more competitive for nodulation over other α- and β-rhizobial strains in a variety of different plant hosts. In order to elucidate the factors that make this bacterium highly competitive for legume infection, we here characterized the type VI secretion system (T6SS) clusters of P. phymatum. T6SSs have been shown to function as a contact-dependent injection system for both bacterial and eukaryotic cells. We identified two T6SS clusters in the genome, created respective mutant strains and showed that they are defective in biofilm formation and in interbacterial competition in vitro. While the T6SS mutants were as efficient as the wild-type in nodulating the non-cognate host Vigna unguiculata, the mutants were less competitive in in planta competition assays, suggesting that the T6SS is one of the factors responsible for the success of P. phymatum in infecting legumes by directly inhibiting competitors.
Insights
Paraburkholderia phymatum utilizes its type VI secretion system (T6SS) to outcompete other rhizobial strains during legume infection. This bacterial T6SS is crucial for inhibiting competitors, enhancing P. phymatum
Area of Science:
- Microbiology
- Plant-Bacterial Interactions
- Symbiotic Relationships
Background:
- Paraburkholderia phymatum is a potent microsymbiont of Mimosa spp. and nodulates various legumes.
- P. phymatum exhibits high competitiveness against other rhizobial strains in diverse plant hosts.
- Understanding the factors driving P. phymatum's competitive success is essential for optimizing legume symbiosis.
Purpose of the Study:
- To characterize the type VI secretion system (T6SS) clusters in P. phymatum.
- To elucidate the role of T6SS in the competitiveness of P. phymatum during legume infection.
Main Methods:
- Identification of two T6SS clusters in the P. phymatum genome.
- Construction and analysis of T6SS mutant strains.
- In vitro assays for biofilm formation and interbacterial competition.
- In planta competition assays with Vigna unguiculata.
Main Results:
- T6SS mutants showed defects in biofilm formation and in vitro interbacterial competition.
- T6SS mutants retained nodulation efficiency on non-cognate hosts.
- T6SS mutants exhibited reduced competitiveness during in planta assays.
Conclusions:
- The type VI secretion system (T6SS) is a key factor contributing to P. phymatum's competitive advantage in legume infection.
- TSS mediates the inhibition of competing bacteria during the symbiotic process.
- TSS contributes to the success of P. phymatum in establishing symbiotic relationships with legumes.
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