The search for Lactobacillus proteins that bind to host targets : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University, Turitea, New Zealand
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Date
2014
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Massey University
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Abstract
Interactions between microorganisms and host cells in the gastrointestinal tract
are crucial to the host’s health. Probiotic bacteria, such as the lactobacilli provide
numerous benefits to human health thought to be mediated by bacterial proteins called
effectors. Lactobacillus rhamnosus HN001 (L. rhamnosus HN001) is a cheesefermenting
isolate with probiotic characteristics and Lactobacillus reuteri 100-23 (L.
reuteri 100-23) is a coloniser of the rodent forestomach. Whereas L. rhamnosus HN001
was shown to reduce eczema in children, L. reuteri 100-23 reduces inflammation in
mice. The effector proteins for these strains are largely unknown. In this thesis, phage
display technology was used to search for proteins that bind specific ligands. Shot-gun
genomic phage display library of L. rhamnosus HN001 was affinity screened on
fibronectin as bait, leading to enrichment of specific recombinant clones. Analysis of 10
candidate clones, however, determined that these are not genuine binders, but may have
been selected due to a potential growth advantage during amplification steps of the
library. The L. reuteri 100-23 genomic shot-gun phage display library was subjected to
two affinity screens on two baits: fibronectin and murine stomach tissue. The aim of the
screen on the murine stomach tissue was to identify keratin-binding proteins, as this
strain naturally colonises the murine keratinous forestomach. Whereas no enrichment
was detected in the screen on fibronectin as a bait, a strong enrichment of a phagemid
displaying a short peptide, IGINS, derived from a cell-surface protease of L. reuteri
100-23 was identified. Identifying and characterising probiotic bacterial proteins that
positively influence health will lead to a greater understanding of gastrointestinal tract
interactions. Ultimately, this aids development of probiotic use as therapeutic agents.
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Keywords
Probiotic bacteria, Lactobacillus, Lactobacillus rhamnosus, Lactobacillus reuteri, Keratin-binding proteins, Probiotics, Research Subject Categories::NATURAL SCIENCES::Biology::Cell and molecular biology