Tripathi Prachi

  PhD project of Prachi Tripathi

Nanoscale study of the structure, properties and interactions of pili from the probiotic bacterium Lactobacillus rhamnosus GG

I am currently enrolled as a doctoral student at the Katholieke Universiteit Leuven. I belong to the Salmonella and Probiotics team of Professor Jos Vanderleyden, located at the Centre of Microbial and Plant Genetics. The group broadly aims to elucidate the mechanisms of bacterial-host interactions and utilize this knowledge to prevent harmful interactions and promote the beneficial ones. Apart from research work, I also follow courses in topics relevant to my research such as Scanning Probe Microscopy and Microbial Biotechnology.

Bacterial pili are extremely important structures as they have been implicated in crucial host-microbe interactions, colonization, tropism determination, biofilm formation, invasion and signaling events [1]. I am interested in understanding how /Lactobacillus rhamnosus/ GG (LGG) probiotic bacteria adhere and interact with host tissues, and in identifying the surface molecules, particularly pili, that determine these properties [2]. LGG has unique heteropolymeric pili on its surface that have been found to contain a human-mucus binding protein [3]. However, the biophysical properties and molecular interactions of these pili remain essentially unknown. In the frame of a close collaboration between the Vanderleyden group (CMPG, KUL) and the Dufrêne group (IMCN, BSMA, UCL), my project aims at gaining new insights into the nanoscale structure, properties and interactions of LGG pili with the ultimate goal of understanding the molecular mechanisms underlying their interaction with human host tissues. We also expect to shed light on pili-mediated interactions among bacterial cells, which might have important consequences for understanding colonization and biofilm formation by LGG. The general strategy involves improving atomic force microscopy (AFM) techniques [4] for pili analysis (advanced procedures for sample preparation and tip modifications, high-resolution imaging, single-molecule manipulations), and applying these nanotools to a range of L. rhamnosus GG mutants altered in their cell wall constituents (pili, polysaccharides).

AFM images showing fascinating star-like (left, image size 3.2 µm) and bundle (right, image size 18.8 µm) patterns formed by LGG pili on mica surfaces.

[1] Kline, K.A., Dodson, K.W., Caparon, M.G. and Hultgren, S.J. (2010) A tale of two pili: assembly and function of pili in bacteria. Trends in Microbiol. 18, 224-232.
[2] Lebeer, S., Vanderleyden, J., De Keersmaecker, S.C.J. (2010) Host interactions of probiotic bacterial surface molecules: comparison with commensals and pathogens. Nat. Rev. Microbiol., 8, 171-184.
[3] Kankainen, M., et al. (2009) Comparative genomic analysis of /Lactobacillus rhamnosus /GG reveals pili containing a human mucus binding protein. PNAS USA 106, 17193-17198.
[4] Müller, D.J. and Dufrêne, Y.F. (2008) Atomic force microscopy as a multifunctional molecular toolbox in nanobiotechnology. Nature Nanotechnology 3, 261-269.