This doctoral thesis, directed by Amparo Latorre Castillo and Carlos García Ferris, analyzes the interaction metabolism between the members of the symbiotic system of the German cockroach Blattella germanica, formed by the endosymbiont Blattabacterium, the intestinal microbiota and the host itself. Part of the results of the thesis have been published in the journals NAR Genomics and Bioinformatics and Journal of Pharmaceutical and Biomedical Analysis. The thesis was defended on March 25, 2021.

The main objective of the thesis “Understanding the dialogue between the gut microbiota and the endosymbiont in the model system Blattella germanica” has been to understand why cockroaches have two symbionts (Blattabacterium and the intestinal microbiota), and if there is a dialogue between them and the host. First, the molecular communication between the endosymbiont and the host was studied, as well as the interaction between the endosymbiont and the intestinal microbiota. The analysis and integration of various omics techniques allowed the study of the functions of this microbiota. To describe the molecular mechanisms that allow the transport of metabolites between the cockroach and its endosymbiont, possible membrane transporters were cloned in yeast and their function was analyzed. The effect of reducing the endosymbiont population on the rest of the system, through antibiotic treatment with rifampicin, was also studied. It was observed that the endosymbiont has an essential role in the development of the host that cannot be supplied by the intestinal microbiota, although it can survive with its highly reduced population. However, it was demonstrated for the first time that the intestinal microbiota is capable of self-regulation and is not modified by these changes. These results, given thatB. germanicais an important pest, they open doors to studies with cockroaches lacking endosymbiont (aposymbiotic). Finally, the intestinal microbiota was analyzed with three omics techniques and a bioinformatics program was developed that allows its analysis and integration in an automated way, in collaboration with the Robert Koch Institut (Berlin). This program, called gNOMO, also allows host information to be analyzed in parallel, which is of great interest for the study of the microbiota of non-model organisms.

Maria Muñoz Benavent's thesis has been carried out in the Evolutionary Genetics laboratory of the I²SysBio under the supervision of Amparo Latorre Castillo (Professor of Genetics at the University of Valencia UV) and Carlos García Ferris (tenured professor of Biochemistry and Molecular Biology at the UV). During the development of this thesis, Maria Muñoz Benavent was the beneficiary of a contract from the FPU University Teacher Training program of the MICIU, and carried out a research stay at the Robert Koch Institut in Berlin with a scholarship from the UV. The panel was made up of Francisco J. Silva Moreno (UV), Laura Gómez Valero (Institut Pasteur, Paris) and Rafel Patiño Navarrete (Sorbonne Université, Paris), who rated the thesis as outstanding.