Toxic sponges & pharmaceutical properties
Sponges feed by filtering seawater that contains nutrients, minerals and also the toxins excreted by other animals and plants. They may reuse (sequester) these toxins for their own metabolic functions (secondary metabolites). Sponges also produce their own toxins through normal metabolism, or in collaboration with the many microbes that live inside them. Whatever the source of these toxic chemicals, many have been found to be highly toxic to other life forms. In fact some of the most toxic chemicals known in nature have been discovered from sponges. Some of these chemicals have potential pharmaceutical applications, including anti-cancer, anti-malaria and pain control (analgesics). In fact the major reason why our knowledge of sponges has escalated over the past few decades is directly due to the increasing interest in their pharmaceutical properties.
Stylissa flabellata (and a crinoid feather-star ‘guest’), a natural source of the bioactive chemical Flabellazole A.
Chemical structure of Flavellazole A discovered from the sponge Stylissa flabellata from the Great Barrier Reef. Flavellazole A is effective as a specific antagonist for P2X7 (pain) receptors and for the potential treatment of inflammatory diseases.
Citronia sp. from the outer reefs of the Great Barrier Reef, a natural source of the bioactive compound Dysinosin A.
Dysinosin A discovered from the sponge Citronia sp, from the Great Barrier Reef, found to inhibit the blood clotting enzymes, thrombin and Factor VIIa, with potential applications to treating human cardiovascular disorders such as stroke and thrombosis.
There are also many biological reasons why sponges are much more toxic than most other marine invertebrates, related to evolutionary advantages of being toxic (the study of chemical ecology).
- Chemical defence. Since sponges cannot avoid predators by escaping, they may use toxins to repel predators.
Monanchora unguiculata, with fish feeding on the sponge.
Two nudibranch molluscs, Helgerta sp., feeding on a thinly encrusting red sponge and an algal mat.
Synaptula sp. holothurians (echinoderms) feeding on mucus exudate of the sponge Haliclona sp.
- Chemical offence. In highly crowded communities such as coral reefs, space and other resources are limited, and being toxic gives an advantage to out-compete other marine invertebrates for space.
Myrmekioderma granulata sponge with an epizootic didemnid ascidian and other sessile marine invertebrates and plants competing for space. Sponges often win this competition due to their high toxicity.
Sponges and other sessile marine invertebrates competing for living space in a crowded community in a shaded coral reef habitat.
- Bioerosion. Some groups of sponges specialize in excavating coral and other calcium carbonate reef structures. These sponges have special cells that produce chemical compounds (acid phosphatase and lysosomal enzymes) which break down the calcium carbonate in small chips and make it available again (recycle) to other animals and plants on the reef.
Cliona sp. excavating and covering surface of a dead coral head, with a massive exhalant breathing pore (oscule) and the water canal system clearly visible internally. Cliona species are responsible for much of the bioerosion and recycling of calcium carbonate in coral reefs.
Spirastrella sp., alpha stage growth form invading and excavating coral skeletons. These sponges etch the calcium carbonate as chips to recycle calcium back into the reef system.
- Chemical recognition. Interactions among many life forms happen at a chemical level, including recognising friends (commensals) from enemies (predators, parasites). Chemical signals may be one reason why some species are able to live in or on sponges but others not.
Small Suberites sp. sponge covered with ophiuroid echinoderm sea stars.
- Anti-parasitic. Toxins may repel unwanted free-loaders settling on or in a sponge.
Trikentrion flabelliforme sponge with a parasitic (epizootic) zooanthid coral, Palythoa sp., on its exterior surface.
- Antibiotic. The ability of cells to recognise foreign cells is the basis of modern immunology theory (self not-self recognition), through chemical signals. Sponges were pivotal to this discovery and the development of our understanding of how antibiotics work.
The sponge Mycale sp. encrusting on a zooanthid Palythoa sp., also with parasitic scyphozoans polyps, didemnid ascidians and hydroids growing on the surface.
- Species interactions. There is a myriad of other animals, plants and microbes that live inside and outside sponges, in the body (mesohyl) or within their cells, some of these having co-evolved in a mutually beneficial (symbiotic) relationship, others just guests or pests passing through. Some sponges are said to have more bacterial cells in their bodies than their own cells, and sponges have also become known as ‘sponge hotels’. These species interactions may produce unique chemistries not possible with each species living in isolation.
Trumpet sponge Cribrochalina vasiformis with a crinoid echinoderm feather star as a ‘sponge hotel’ guest.
- Ancient geological history. Sponges have the most ancient of origins (Precambrian Ediacaran Period, between 600-530 million years ago). Consequently they have had many millions of years to experiment with their biosynthetic pathways, and while today they may be biochemically diverse they appear to be morphologically conservative. Sponges were well-established by the Lower Cambrian Period (more than 570 million years ago), and were major reef builders during the Devonian Period (more than 370 million years ago), before reef-building corals out-competed them as primary reef builders. Many species alive today are morphologically identical to those that lived at the beginning of the Cretaceous Period (more than 150 million years ago), giving them the incorrect tag as ‘living fossils’.
The ‘living fossil’ sponge Vaceletia sp., with a hard bodied tubular growth form, found in caves at a remote reef in the Coral Sea, with its closest known ancestor extinct by the end of the Cretaceous Period.
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