Juan Francisco Rodríguez Vidal¹, FERNANDO PÉREZ SANZ², ÁNGEL ESTEBAN GIL³, Teresa Soto Pino⁴, José Cansado Vizoso⁴, Isabel Cabas Sánchez⁵, MARIA LUISA CAYUELA FUENTES⁶, Alfonsa García Ayala⁵, Victoriano Mulero Méndez⁵

(1) Universidad de Murcia, 30168, España (Región de Murcia)
(2) PLATAFORMA DE INFORMÁTICA BIOMÉDICA Y BIOINFORMÁTICA, IMIB-Arrixaca, España
(3) TECNOLOGÍAS DE MODELADO, PROCESAMIENTO Y GESTIÓN DEL CONOCIMIENTO, IMIB-Arrixaca, España
(4) E026-01 FISIOLOGIA MICROBIANA, Universidad de Murcia, España (Región de Murcia)
(5) INMUNIDAD, INFLAMACIÓN Y CÁNCER, IMIB-Arrixaca, España
(6) CIRUGÍA DIGESTIVA, ENDOCRINA Y TRASPLANTE DE ÓRGANOS ABDOMINALES, IMIB-Arrixaca, España

Aging is a complex process of life characterized by a progressive loss of functionality and integrity, being affected by many biological aspects. New molecular mechanisms that take part in the aging process have been recently proposed including the immune system or the microbiota. Our immune system is remodeled throughout lifespan reaching an “immunosenescence” state in older ages. This state is distinguished by a decrease in naïve T and B cells and an increase in both the memory subpopulations and the production of pro-inflammatory cytokines, being this latter mainly driven by macrophages which results in a chronic low-grade inflammation termed as “Inflammaging”. Gut microbiota is another key factor that contributes to homeostasis and disease, regulating several biological processes, changing its diversity with age and the state of health and being able to extend the lifespan by the transference of fecal microbiota from young individuals to older ones. In this context, the vast majority of studies have only taken into consideration the bacterial microbiota, while the implications of the fungal microbiota, also termed as mycobiota, are starting to be elucidated.

The rag1 mutant zebrafish, traditionally considered as a Severe Combined Immunodeficiency (SCID) model (OMIN 179615), is a great immunodeficiency-induced aging model. This mutant fish lacks functional T and B cells and at the same time shows an accelerated aging phenotype due to the increase in the activation of the innate immune system in a similar way to immunodeficiency conditions. Based on this, a metagenomic sequencing was performed on gut samples from both wild-type and rag1 mutant fish to uncover the bacterial diversity in premature aging induced by an immunodeficiency state. We also performed a Fecal Microbiota Transplant (FMT) from healthy donors to mutants and vice versa. In addition, a characterization of the intestinal yeast diversity was carried out by isolating yeasts colonies in culture from gut samples and identifying them by sequencing.

As preliminary results, the rag1 mutant zebrafish showed an altered bacterial diversity including severe changes in the proportion of different groups, such as an increase in the Proteobacteria phylum, while a decrease in other phyla like Fusobacteria, Bacteroidetes or Tenericutes, together with a reduced alpha-diversity. This microbiota profile is consistent with the changes that are observed during the aging process in other fish species. The performance of a FMT from wild-type fish to rag1 mutants led to a partial restoration of the bacterial composition in the transplanted individuals. Surprisingly, the wild-type individuals transplanted with a mutant fish-microbiota underwent a profound alteration of their bacterial composition, resembling the mutant’s one. The yeast diversity of the mutant fish seems to be reduced since only one species of yeast was identified from the mutant samples versus a total of eight different species identified from the wild-type samples.

The results obtained from this study show up the strong influence that the immune system exerts on the shaping of the gut microbiota diversity as the rag1 mutant zebrafish, who lacks the adaptive immune compartment and have an exacerbated inflammation, shows an abrupt change in its gut microbiota composition. In the near future, we will try to figure out the implications of these microbial groups in general health and lifespan.