Sponges have co-evolved for millions of years alongside several types of microorganisms, which aside from participating in the animal's diet, are mostly symbionts. Since most of the genetic repertoire in the holobiont genome is provided by microbes, it is expected that the host-associated microbiome will be at least partially heritable. Sponges can therefore acquire their symbionts in different ways. Both vertical transmission (VT) and horizontal transmission (HT) have different advantages and disadvantages in the life cycle of these invertebrates. However, a third mode of transmission, called leaky vertical transmission or mixed mode of transmission (MMT), which incorporates both VT and HT modes, has gained relevance and seems to be the most robust model. In that regard, the aim of this review is to present the evolving knowledge on these main modes of transmission of the sponge microbiome. Our conclusions lead us to suggest that MMT may be more common for all sponges, with its frequency varying across the transmission spectrum between species and the environment. This hybrid model supports the stable and specific transmission of these microbial partners and reinforces their assistance in the resilience of sponges over the years.

ResumenSe muestrearon 20 ejemplares (alevines y juveniles) de trucha arco iris cultivados en la piscifactoría Acochinchán (Canta, Lima, Perú), y se les aplico la técnica de la Reacción en Cadena de la Polimerasa (PCR) con la finalidad de obtener una identificación rápida del agente patógeno Yersinia ruckeri que produce la enfermedad entérica de la boca roja (ERM) y genera elevadas tasas de mortalidad. Nueve ejemplares fueron asintomáticos mientras que 11 presentaron signos de ERM. Se aislaron 22 cepas bacterianas del hígado, bazo y riñón. Se empleó la técnica de la PCR para la amplificación y cebadores específicos (ARNr 16S), que permitieron amplificar un fragmento de ADN de 575 pb de Yersinia ruckeri. Diecinueve cepas fueron identificadas como Yersinia ruckeri mediante la PCR, tanto en peces sintomáticos como asintomáticos. Se estableció un tiempo de diagnóstico de 26 horas, en comparación con los 2 ó 3 días que duraría el diagnóstico empleando las pruebas bioquímicas. Palabras Clave: Yersinia ruckeri, Oncorhynchus mykiss, PCR, diagnóstico, Enfermedad Entérica de la BocaRoja. AbstractTwenty individuals of rainbow trout were sampled (fry and juveniles) from Acochinchan Fishfarm (Canta, Lima -Peru), and analyzed with the Polimerase Chain Reaction test (PCR ) in order to achieve a rapid identification of Yersinia ruckeri, which is the pathogen agent that causes the enteric red mouth disease (ERM) and produces high rates of mortality. Nine fish samples were asymptomatic, while 11 of them showed signs of ERM. In addition, 22 bacterial strains were isolated from the liver, spleen and kidney. PCR and specific primers (16S rRNA), were used to amplified a specific 575 bp DNA fragment of Yersinia ruckeri. Nineteen strains were identified as Yersinia ruckeri by PCR in symptomatic and asymptomatic fishes. It was established a diagnosis time of 26 hours, compared with the 2 or 3 days that would take the diagnosis using biochemical tests.

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