Rhodobacteraceae dominate the core microbiome of the sea star Odontaster validus (Koehler, 1906) in two opposite geographical sectors of the Antarctic Ocean

Abstract

Microbiota plays essential roles in the health, physiology, and in adaptation of marine multi-cellular organisms to their environment. In Antarctica, marine organisms have a wide range of unique physiological functions and adaptive strategies, useful for coping with extremely cold conditions. However, the role of microbiota associated with Antarctic organisms in such adaptive strategies is underexplored. In the present study, we investigated the diversity and putative functions of the microbiome of the sea star Odontaster validus, one of the main keystone species of the Antarctic benthic ecosystems. We compared the whole-body bacterial microbiome of sea stars from different sites of the Antarctic Peninsula and Ross Sea, two areas located in two opposite geographical sectors of the Antarctic continent. The taxonomic composition of O. validus microbiomes changed both between and within the two Antarctic sectors, suggesting that environmental and biological factors acting both at large and local scales may influence microbiome diversity. Despite this, one bacterial family (Rhodobacteraceae) was shared among all sea star individuals from the two geographical sectors, representing up to 95% of the microbial core, and suggesting a key functional role of this taxon in holobiont metabolism and well-being. In addition, the genus Roseobacter belonging to this family was also present in the surrounding sediment, implying a potential horizontal acquisition of dominant bacterial core taxa via host-selection processes from the environment.

Keywords: Antarctica; Odontaster validus; geographic location; microbial diversity; microbiome.

Figure 1

Box plots of ASV richness (A), Shannon (B) and the Pielou’s Evenness (C) indices of alpha-diversity of microbiomes associated with individuals of Odontaster validus collected in the different Antarctic sites of the Antarctic Peninsula and Ross Sea areas. The “x” within each box plot indicates the average value.

Figure 2

MDS analysis comparing the taxonomic composition of microbiomes associated with individuals of Odontaster validus collected in the different Antarctic sites of the Antarctic Peninsula and Ross Sea areas. Percentages in blue refer to the dissimilarities between Port Foster Bay and the different Ross Sea sites; percentages in red refer to the dissimilarities among the sites within the Ross Sea area.

Figure 3

Main bacterial taxa responsible for the differences between microbiomes associated with Odontaster validus collected in the Antarctic Peninsula and the Ross Sea areas (A). Main bacterial taxa responsible for the differences among microbiomes associated with O. validus collected in the different benthic sites within the Ross Sea area (B). Comparisons were performed used as statistical test the White’s non-parametric t-test (value of p < 0.05).

Figure 4

Heatmap showing the relative abundances of the main microbial taxa of individuals of Odontaster validus collected in the different Antarctic sites (Statistical test: ANOVA; Post-hoc test: Welch’s; value of p < 0.05).

Figure 5

Relative abundance composition of the predicted functions related to microbiomes associated with individuals of Odontaster validus collected in the different sites of the Antarctic Peninsula and Ross Sea areas.

Figure 6

Heatmap showing the relative abundances of the main microbial taxa responsible for the significant differences between individuals of Odontaster validus and surrounding sediments (Statistical test: ANOVA; Post-hoc test: Welch’s; value of p < 0.05) (A). Contribution of all the bacterial genera within the Rhodobacteraceae family detected in the microbiomes associated with O. validus and in those living in the surrounding sediments (B).