Abstract
Sponges are engaged in intimate symbioses with a diversity of microorganisms from all three domains of life, namely Bacteria, Archaea and Eukarya. Sponges have been well studied and categorized for their bacterial communities, some displaying a high microbial abundance (HMA), while others show low microbial abundance (LMA). However, the associated Archaea and Eukarya have remained relatively understudied. We assessed the bacterial, archaeal and eukaryotic diversities in the LMA sponge species Dysidea avara and Dysidea etheria by deep amplicon sequencing, and compared the results to those in the HMA sponges Aplysina aerophoba and Aplysina cauliformis. D. avara and A. aerophoba are sympatric in the Mediterranean Sea, while D. etheria and A. cauliformis are sympatric in the Caribbean Sea. The bacterial communities followed a host-specific pattern, with host species identity explaining most of the variation among samples. We identified OTUs shared by the Aplysina species that support a more ancient association of these microbes, before the split of the two species studied here. These shared OTUs are suitable targets for future studies of the microbial traits that mediate interactions with their hosts. Even though the archaeal communities were not as rich as the bacterial ones, we found a remarkable diversification and specificity of OTUs of the family Cenarchaeaceae and the genus Nitrosopumilus in all four sponge species studied. Similarly, the differences in fungal communities were driven by sponge identity. The structures of the communities of small eukaryotes such as dinophytes and ciliophores (alveolates), and stramenopiles, could not be explained by either sponge host, sponge genus or geographic location. Our analyses suggest that the host specificity that was previously described for sponge bacterial communities also extends to the archaeal and fungal communities, but not to other microbial eukaryotes.
Highlights
Sponges feature an intimate symbiosis with diverse microorganisms (Taylor et al, 2007; Simister et al, 2012)
We investigated the microbial diversity of the low microbial abundance (LMA) sponge species Dysidea avara and D. etheria and compared it with that of the high microbial abundance (HMA) sponge species Aplysina aerophoba and A. cauliformis
Chao1 values show that α-diversity values in both Aplysina host species and the seawater were significantly higher (F = 20.35, P = 8.55e−05) than those observed for Dysidea host species, confirming previous findings stating that LMA sponge species have lower microbial abundance and lower richness, as compared to HMA sponge species
Summary
Sponges (phylum Porifera) feature an intimate symbiosis with diverse microorganisms (Taylor et al, 2007; Simister et al, 2012). Some species occur in freshwater, we here place a focus on marine sponges. These are sessile filter feeders that acquire organic matter and microorganisms from seawater by pumping large volumes of water through their aquiferous system (Vogel, 1977). Microorganisms can, survive in the mesohyl tissue and become established as part of the sponge-associated microbiota. This process of translocation of microorganisms from seawater to the sponge is referred to as horizontal transmission. Sponges may acquire their associated microbiota by means of vertical transmission, through incorporation of microbial cells in egg cells or other reproductive stages. The acquisition of similar sponge-associated microbes can occur both vertically and horizontally (Sipkema et al, 2015)
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