Interference competition and genetic diversity at the intraspecific scale in the lactic acid bacterium Carnobacterium maltaromaticum

Abstract : Competition and diversity are major phenomena in microbiology. In the agri-food sector, competition is the very basis of biopreservation, a process which objective is to inhibit undesirable microorganisms through the use of microbial competitors. Microbial diversity lies at the origin of the diversity of fermented products and particularly of the typicality of cheeses. However, the ecology of microbial competition in food and the link with microbial diversity are poorly understood. The goal of this thesis was to study the diversity and the competition of a representative model bacterium of the cheese ecosystem. The study model chosen is the lactic acid bacterium Carnobacterium maltaromaticum. An analysis of the diversity of 21 strains of C. maltaromaticum was performed by MultiLocus Sequence Typing (MLST) and allowed to complete the scheme of C. maltaromaticum population structure. This study revealed the presence of 56 genotypes among a collection of 71 strains, showing a high genetic diversity within this species. Interference competition was studied by performing high-throughput competition assays. Each competition assay involved two strains, one in the position of the sender strain and the other in the position of the receiver. In total, 5776 tests were performed on a collection of 76 strains. The results revealed that 60% of strains inhibited at least one other strain of the collection, indicating that intraspecific competition is major in C. maltaromaticum. Moreover, a large variability in the width of inhibition and sensitivity spectra has been observed. A network analysis approach revealed a nested architecture of the competitive network, suggesting that inhibition depends not only on the antagonistic characteristics of the inhibitory strains but also on the level of sensitivity of the receiver strains. A genomic analysis of 26 strains from the collection was performed in order to predict their gene content encoding the synthesis of antagonistic substances, and it allowed the identification of genes potentially encoding bacteriocins. In conclusion, this thesis has shown that the species Carnobacterium maltaromaticum is characterized by a high genetic diversity and that interference competition is frequent in the population
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Theses
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http://docnum.univ-lorraine.fr/ulprive/DDOC_T_2018_0211_RAMIA.pdf
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https://hal.univ-lorraine.fr/tel-02096739
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Submitted on : Thursday, April 11, 2019 - 3:21:19 PM
Last modification on : Friday, April 12, 2019 - 1:24:07 AM

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Nancy Ramia. Interference competition and genetic diversity at the intraspecific scale in the lactic acid bacterium Carnobacterium maltaromaticum. Food engineering. Université de Lorraine; Université libanaise, 2018. English. ⟨NNT : 2018LORR0211⟩. ⟨tel-02096739⟩

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