Cora Miquel-Guennoc\u00a0 d\u00e9fendra publiquement sa th\u00e8se\u00a0Lundi 6 mars \u00e0 14h30\u00a0(amphi 7 FST).<\/p>\n
“Etude de l’interaction physique entre le champignon ectomycorhizien Laccaria bicolor S238N et la bact\u00e9rie auxiliaire de la mycorhization Pseudomonas fluorescens BBc6R8”<\/p>\n
R\u00e9sum\u00e9<\/strong><\/p>\n Dans les sols, les champignons ectomycorhiziens (ECM) forment une symbiose tr\u00e8s r\u00e9pandue\u00a0avec les racines des arbres et contribuent ainsi \u00e0 leur croissance et \u00e0 leur sant\u00e9. Des \u00e9tudes ant\u00e9rieures\u00a0ont montr\u00e9 que certaines bact\u00e9ries pouvaient influencer positivement la symbiose entre les\u00a0ECM et les arbres, appel\u00e9es BAM pour Bact\u00e9ries Auxiliaires de la Mycorhization. Les m\u00e9canismes\u00a0de l\u2019effet auxiliaire des BAM sont encore peu connus. En amont de cette th\u00e8se, il avait \u00e9t\u00e9 montr\u00e9\u00a0in vitro que la BAM Pseudomonas fluorescens BBc6\u00a0formait des structures similaires \u00e0 des\u00a0biofilms sur les hyphes de l\u2019ECM Laccaria bicolor. Dans ce contexte, afin d\u2019enrichir les connaissances\u00a0concernant les interactions entre les ECM et les BAM, cette th\u00e8se a port\u00e9 sur l\u2019interaction\u00a0physique entre ces deux organismes. L\u2019\u00e9tude a en partie \u00e9t\u00e9 r\u00e9alis\u00e9e via une m\u00e9thode d\u2019analyse\u00a0par microscopie confocale, d\u00e9velopp\u00e9e durant cette th\u00e8se. Les r\u00e9sultats obtenus ont montr\u00e9 que\u00a0cette bact\u00e9rie formait des biofilms localis\u00e9s pr\u00e9f\u00e9rentiellement sur la r\u00e9gion apicale des colonies\u00a0de l\u2019ECM ce qui pourrait indiquer une interaction trophique. L\u2019existence d\u2019une telle interaction\u00a0a d\u2019ailleurs par la suite \u00e9t\u00e9 confirm\u00e9e. Les r\u00e9sultats ont \u00e9galement montr\u00e9 que l\u2019interaction physique\u00a0entre L. bicolor et BBc6\u00a0n\u2019est pas sp\u00e9cifique puisque l\u2019ensemble des treize autres souches\u00a0bact\u00e9riennes test\u00e9es a form\u00e9 des biofilms sur les hyphes de L. bicolor. En revanche, BBc6\u00a0s\u2019est\u00a0montr\u00e9e incapable de former des biofilms sur certains champignons appartenant aux Ascomyc\u00e8tes,\u00a0sugg\u00e9rant des m\u00e9canismes d\u2019inhibition. De plus, l\u2019\u00e9tude de la matrice des biofilms form\u00e9s\u00a0par BBc6R8 a r\u00e9v\u00e9l\u00e9 la pr\u00e9sence de r\u00e9seaux de filaments constitu\u00e9s d\u2019ADN qui semblent structurer\u00a0ces biofilms et qui ont aussi \u00e9t\u00e9 observ\u00e9s chez l\u2019ensemble des souches bact\u00e9riennes test\u00e9es. Ces\u00a0r\u00e9sultats r\u00e9v\u00e8lent un r\u00f4le structural de la mol\u00e9cule d\u2019ADN qui, bien qu\u2019il semble r\u00e9pandu, n\u2019a que\u00a0peu \u00e9t\u00e9 report\u00e9 jusqu\u2019\u00e0 pr\u00e9sent. Enfin, il a \u00e9t\u00e9 montr\u00e9 que des mutants de BBc6\u00a0qui ont perdu\u00a0leur effet auxiliaire forment des biofilms diff\u00e9rents de la souche sauvage sur une surface abiotique\u00a0sugg\u00e9rant un lien potentiel entre l\u2019effet auxiliaire et la formation de biofilms.<\/p>\n Abstract<\/strong><\/p>\n In soil ecosystems, ectomycorrhizal fungi (ECM) form a widespread symbiosis with roots of\u00a0trees, contributing to tree growth and health. It has been shown that some bacteria, called mycorrhization\u00a0helper bacteria (MHB), stimulate mycorrhizal symbiosis. The mechanisms of this\u00a0helper effect are poorly understood. Previous studies have shown that the MHB Pseudomonas\u00a0fluorescens BBc6\u00a0formed biofilm-like structures around the hyphae of the ECM Laccaria bicolor\u00a0during their in vitro interaction. In this context, in order to increase knowledge concerning\u00a0MHB \/ ECM interactions, the work presented here focuses on the physical interaction between\u00a0these two organisms. To this purpose, a method of analysis based on confocal microscopy was\u00a0developed. The results showed that the bacteria formed biofilms preferentially localized on the\u00a0apical region of the ECM colonies, which could indicate a trophic interaction. Such an interaction\u00a0has been subsequently confirmed. The results also showed that the physical interaction between L.\u00a0bicolor and BBc6\u00a0is not specific since all thirteen other bacterial strains tested formed biofilms\u00a0on the hyphae of L. bicolor. On the other hand, BBc6\u00a0was unable to form biofilms on some\u00a0fungi belonging to Ascomycetes, suggesting the existence of inhibition mechanisms. Moreover, the\u00a0study of the BBc6\u00a0biofilm matrix revealed networks of DNA-containing filaments which seem\u00a0to structure these biofilms and which have also been observed in all the bacterial strains tested.\u00a0These results reveal a structural role of the DNA molecule, a role that has been rarely reported\u00a0so far despite its probable high occurence. Finally, it has been shown that BBc6R8 mutants having\u00a0lost their helper effect presented a modified phenotype concerning their biofilm formation on\u00a0abiotic surface, suggesting a potential link between the helper effect and the biofilms formation.<\/p>\n","protected":false},"excerpt":{"rendered":" Cora Miquel-Guennoc\u00a0 d\u00e9fendra publiquement sa th\u00e8se\u00a0Lundi 6 mars \u00e0 14h30\u00a0(amphi 7 FST). “Etude de l’interaction physique entre le champignon ectomycorhizien Laccaria bicolor S238N et la bact\u00e9rie auxiliaire de la mycorhization Pseudomonas fluorescens BBc6R8” R\u00e9sum\u00e9 Dans les sols, les champignons ectomycorhiziens … Continue reading