Abstract
Marine ecosystems serve as global carbon sinks and nutrient source or breeding ground for aquatic animals. Sponges are ancient parts of these important ecosystems and can be found in caves, the deep-sea, clear waters, or more turbid environments. Here, we studied the bacterial community composition of the calcareous sponge Clathrina clathrus sampled close to the island Corsica in the Mediterranean Sea with an emphasis on planctomycetes. We show that the phylum Planctomycetes accounts for 9% of the C. clathrus-associated bacterial community, a 5-fold enrichment compared to the surrounding seawater. Indeed, the use of C. clathrus as a yet untapped source of novel planctomycetal strains led to the isolation of strain KS4T. The strain represents a novel genus and species within the class Phycisphaerae in the phylum Planctomycetes and displays interesting cell biological features, such as formation of outer membrane vesicles and an unexpected mode of cell division.
Highlights
Aquatic ecosystems comprise biological communities of organisms, which together shape a local habitat
The 16S rRNA gene sequence-based phylogeny was computed for strain KS4T, the type strains of all described planctomycetal species and all isolates recently published and described (Boersma et al, 2019; Kallscheuer et al, 2019a,b,c, 2020; Dedysh et al, 2020; Kohn et al, 2020a; Peeters et al, 2020)
In order to get an unbiased impression of the bacterial diversity associated with C. clathrus, we followed a cultivation-independent approach based on 16S rRNA gene amplicon sequencing
Summary
Aquatic ecosystems comprise biological communities of organisms, which together shape a local habitat. Once attached to a biotic surface, e.g., a macroscopic phototroph, planctomycetes are thought to use released polysaccharides as carbon and energy source probably using a specialized system for uptake of entire high-molecular weight sugar molecules and subsequent intracellular degradation (Boedeker et al, 2017) Employing such a system represents a decisive advantage compared to other, often faster growing bacteria inhabiting the same ecological niche, e.g., members of the “Roseobacter group” (Frank et al, 2015). The recent development of novel tools and laboratory techniques motivated us to reinvestigate calcareous sponges for the occurrence of planctomycetes (Jogler and Jogler, 2013; Wiegand et al, 2020) For this purpose, we included a cultivation-independent analysis of the bacterial community of C. clathrus sampled near the coast of the island Corsica in the Mediterranean Sea (Figures 1A–C). The large observed differences in the natural abundance of planctomycetes on different marine biotic surfaces (ranging from
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