Pagán-Jiménez M et al. (2019), Characterization of the intestinal microbiota o...

ECB-ART-46921

PLoS One 2019 Jan 01;141:e0208011. doi: 10.1371/journal.pone.0208011.

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Characterization of the intestinal microbiota of the sea cucumber Holothuria glaberrima.

Pagán-Jiménez M , Ruiz-Calderón JF , Dominguez-Bello MG , García-Arrarás JE .

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High-throughput 16S rRNA gene sequencing has been used to identify the intestinal microbiota of many animal species, but that of marine invertebrate organisms remains largely unknown. There are only a few high-throughput sequencing studies on the intestinal microbiota of echinoderms (non-vertebrate Deuterostomes). Here we describe the intestinal microbiota of the sea cucumber Holothuria glaberrima, an echinoderm, well-known for its remarkable power of regeneration. We characterized the microbiota from the anterior descending intestine, the medial intestine (these two comprise the small intestine) and the posterior descending intestine (or large intestine), using pyrosequencing to sequence the V4 region of the 16S rRNA gene. We compared animals in their natural marine environment and in sea-water aquaria. A total of 8,172 OTU''s were grouped in 10 bacterial phyla, 23 classes, 44 orders, 83 families, 127 genera and 1 group of unknown bacteria, present across the digestive tract of 10 specimens. The results showed that the anterior intestine is dominated by Proteobacteria (61%) and Bacteroidetes (22%), the medium intestine is similar but with lower Bacteroidetes (4%), and the posterior intestine was remarkably different, dominated by Firmicutes (48%) and Bacteroidetes (35%). The structure of the community changed in animals kept in aquaria, which had a general dominance of Firmicutes and Bacteroidetes, regardless the intestinal segment. Our results evidence that in the natural sea environment, there is intestinal segment differentiation in the microbiota of H. glaberrima, which is lost in artificial conditions. This is relevant for physiological studies, such as mechanisms of digestive regeneration, which might be affected by the microbiota.

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Genes referenced: LOC100887844 LOC115925415

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	Fig 1. Anatomy of the digestive tract of the sea cucumber H. glaberrima.The digestive tract of H. glaberrima is formed by a continuous tube that begins at the mouth, forming a short esophagus which is attached to a long descending small intestine (anterior) and a long ascending small intestine (medial). The final segment of the tube is a descending large intestine (posterior) that ends in the cloacae. (Diagram obtained from Mashanov et al. 2012. Adapted by MPJ).
	Fig 2. Bacterial taxa distribution in the intestinal system of H. glaberrima.(A) Phylum and Genera of intestinal bacterial OTUs of animals in the sea (natural environment). B) Phylum and Genera of intestinal bacterial OTUs of animals in seawater tanks (aquarium environment).
	Fig 3. Principal Coordinate Analyses (PcoA) of bacterial communities in the intestine of H. glaberrima.Samples clustered using PcoA of weighted UniFrac distance matrices that reflect the beta-diversity of the bacterial communities. The graph shows the UniFrac distance of bacterial communities from the anterior, medial and posterior intestine of the sea cucumber H. glaberrima.
	Fig 4. Principal Coordinate Analyses (PcoA) of bacterial communities in the intestine of H. glaberrima in two different environmental settings.The PcoA analysis reflects the beta-diversity of the bacterial communities from the various intestinal segment samples that originate from two environments; the animals collected in their natural sea environment and animals kept in seawater aquaria for 3 days.
	Fig 5. Proposed endogenous bacterial community of H. glaberrima intestine.We propose that the microbiota found in the posterior intestine of the sea cucumber, either in their natural habitat (ocean) or aquarium environments represents the endogenous microbiota of these animals.

References [+] :

Battistuzzi, A major clade of prokaryotes with ancient adaptations to life on land. 2009, Pubmed