Abundance and Bioactivity of Cultured Sponge-Associated Bacteria from the Mediterranean Sea |
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Authors: | Albrecht Muscholl-Silberhorn Vera Thiel Johannes F Imhoff |
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Institution: | (1) Leibniz-Institut für Meereswissenschaften IFM-GEOMAR, Düsternbrooker Weg 20, 24105 Kiel, Germany |
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Abstract: | In this study, the search for new antibiotics was combined with quantitative ecological studies. The cultured fraction of
the associated bacterial communities from ten different Mediterranean sponge species was investigated. To obtain quantitative
and qualitative data of sponge-associated bacterial communities and to expand the cultured diversity, different media were
used. The largest morphological diversity and highest yield of isolates was obtained by using oligotrophic media, which consisted
of natural habitat seawater amended with (1% additional carbon sources. The dominant bacterial morphotypes were determined
and bacterial isolates were tested for antimicrobial activity and identified using 16S rDNA sequencing. The sponge-associated
most abundant morphotypes were all affiliated to the Alphaproteobacteria and showed antimicrobial activity against at least one of the tested strains. In contrast, the ambient seawater was dominated
by Gammaproteobacteria. One single alphaproteobacterium, which was related to Pseudovibrio denitrificans, was shown to dominate the cultured community of at least six of the sponges. This designated MBIC3368-like alphaproteobacterium
has been isolated from sponges before and seems to be restricted to associations with members of the phylum Porifera. It displays
a weak and unstable antimicrobial activity, which gets easily lost during cultivation. However, this bioactive bacterium was
present in the sponges by up to 106 cells per gram wet-weight sponge tissue and dominated the cultured fraction with up to 74%. The association of this alphaproteobacterium
with sponges is probably evolutionary young and facultative and possibly involves biologically active secondary metabolites.
Besides a demonstrated vertical transfer, additional horizontal transfer between the sponges is assumed. Members of the genus
Bacillus displaying antimicrobial activity were found regularly, too. However, actinomycetes, which are known for their production
of bioactive substances, were present in very low abundance. |
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