Oxygen-Controlled Bacterial Growth in the Sponge Suberites domuncula : toward a Molecular Understanding of the Symbiotic Relationships between Sponge and Bacteria

Abstract

Sponges (phylum Porifera), known to be the richest producers among the metazoans of bioactive secondary metabolites, are assumed to live in a symbiotic relationship with microorganisms, especially bacteria. Until now, the molecular basis of the mutual symbiosis, the exchange of metabolites for the benefit of the other partner, has not been understood. We show with the demosponge Suberites domuncula as a model that the sponge expresses under optimal aeration conditions the enzyme tyrosinase, which synthesizes diphenols from monophenolic compounds. The cDNA isolated was used as a probe to determine the steady-state level of gene expression. The gene expression level parallels the level of specific activity in sponge tissue, indicating that without aeration the tyrosinase level drops drastically; this effect is reversible. The SB2 bacterium isolated from the sponge surface grew well in M9 minimal salt medium supplemented with the dihydroxylated aromatic compound protocatechuate; this carbon source supported growth more than did glucose. From the SB2 bacterium the protocatechuate gene cluster was cloned and sequenced. This cluster comprises all genes coding for enzymes involved in the conversion of protocatechuate to acetyl coenzyme A. Expression is strongly induced if the bacteria are cultivated on M9-protocatechuate medium; the genes pcaQ (encoding the putative transcriptional activator of the pca operon) and pcaDC were used for quantitative PCR analyses. We conclude that metabolites, in this case diphenols, which might be produced by the sponge S. domuncula are utilized by the sponge surface-associated bacterium for energy generation. This rationale will help to further uncover the symbiotic pathways between sponges and their associated "nonculturable" microorganisms; our approach is flanked by the establishment of an EST (expressed sequence tags) database in our laboratory.

Sponge-Associated Microorganisms: Evolution, Ecology, and Biotechnological Potential

“…The bacterium can obtain protocatechuate in situ from the sponge, which produces this and other diphenols via the activities of the enzyme tyrosinase. Interestingly, tyrosinase activity and expression of the tyrosinase-encoding gene in S. domuncula, as well as the number of pcaDC genes in strain SB2 (responsible for bacterial utilization of protocatechuate and used here as a proxy for SB2 abundance on the surface [exopinacoderm] of the sponge), were all maximal under aerated conditions (241). Coupled with the observed loss of SB2 cells from the sponge surface under low-oxygen conditions, it was asserted that the oxygen level is responsible for regulating the bacterial fauna in sponges.…”

“…In another recent study from the Müller group, using S. domuncula and its alphaproteobacterial symbiont SB2 as a model system, the importance of oxygenation of sponge tissue in mediating the relationship was demonstrated (241). Specifically, it was shown that strain SB2 grew preferentially on minimal media with the aromatic compound protocatechuate, rather than glucose, as the carbon source.…”

“…As discussed at length in the previous section, the fundamental question of symbiont origin (i.e., whether symbionts were passed down from an ancestral sponge or obtained contemporaneously from seawater) remains unresolved, as do many of the mechanisms of sponge-microbe interactions and the regulation of microbial communities in these hosts. Extensive studies by Müller and colleagues have attempted to address the underlying bases of sponge-microbe interactions at the molecular level (36,241,243,249,399,400,444,465). Sponges are often regarded as primitive animals, yet their morphological simplicity belies the possession of a surprisingly complex immune system (244).…”

Phylogenetic diversity and community structure of sponge-associated bacteria from mangroves of the Caribbean Sea

“…The establishment of this relationship relies on mutual recognition between the sponge and its microbial partners, and also on physical competition among the microbial communities themselves (Wilkinson 1984, Müller & Müller 2003, Müller et al 2004). In accordance with this hypothesis, sponges inhabiting the same ecological niche tend to harbor similar microbial communities.…”

Antimicrobial and Antioxidant Activities of Bacterial Extracts from Marine Bacteria Associated with Sponge <i>Stylotella</i> sp.

“…These mixtures were separated and the ethyl acetate layers were evaporated using rotary evaporator at 40°C. The extracts were vacuumed and stored below 5°C for further test (Muller et al, 2004).…”