Giorgio Bavestrello

The temperature-signaling cascade in sponges involves a heat-gated cation channel, abscisic acid, and cyclic ADP-ribose.

Sponges (phylum Porifera) are the phylogenetically oldest metazoan animals, their evolution dating back to 600 million years ago. Here we demonstrate that sponges express ADP-ribosyl cyclase activity, which converts NAD+ into cyclic ADP-ribose, a potent and universal intracellular Ca2+ mobilizer. In Axinella polypoides (Demospongiae, Axinellidae), ADP-ribosyl cyclase was activated by temperature increases by means of an abscisic acid-induced, protein kinase A-dependent mechanism. The thermosensor triggering this signaling cascade was a heat-activated cation channel. Elucidation of the complete thermosensing pathway in sponges highlights a number of features conserved in higher organisms: (i) the cation channel thermoreceptor, sensitive to heat, mechanical stress, phosphorylation, and anesthetics, shares all of the functional characteristics of the mammalian heat-activated background K+ channel responsible for central and peripheral thermosensing; (ii) involvement of the phytohormone abscisic acid and cyclic ADP-ribose as its second messenger is reminiscent of the drought stress signaling pathway in plants. These results suggest an ancient evolutionary origin of this stress-signaling cascade in a common precursor of modern Metazoa and Metaphyta.

Three-dimensional chitin-based scaffolds from Verongida sponges (Demospongiae: Porifera). Part I. Isolation and identification of chitin.

Marine invertebrate organisms including sponges (Porifera) not only provide an abundant source of biologically active secondary metabolites but also inspire investigations to develop biomimetic composites, scaffolds and templates for practical use in materials science, biomedicine and tissue engineering. Here, we presented a detailed study of the structural and physico-chemical properties of three-dimensional skeletal scaffolds of the marine sponges Aiolochroia crassa, Aplysina aerophoba, A. cauliformis, A. cavernicola, and A. fulva (Verongida: Demospongiae). We show that these fibrous scaffolds have a multilayered design and are made of chitin. (13)C solid-state NMR spectroscopy, NEXAFS, and IR spectroscopy as well as chitinase digestion and test were applied in order to unequivocally prove the existence of alpha-chitin in all investigated species.

Metabolic integration between symbiotic cyanobacteria and sponges: a possible mechanism

Metabolic relationships between symbiotic cyanobacteria and host sponge have been investigated in the marine species Chondrilla nucula and Petrosia ficiformis (collected in the Ligurian Sea in 1992). DNA, RNA, total protein, cytosolic protein, total sugar, cytosolic sugar, total lipid, nonprotein sulfhydryl groups, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were assayed in cortex-free sponge tissue, where cyanobacteria are all but absent. For both species, biochemical parameters were determined in specimens living in illuminated habitats and in dark caves, where sponges are virtually aposymbiotic for cyanobacteria. As C. nucula is unable to colonize dark sites, specimens of this species were artificially transferred to a cave and maintained in dark conditions for 6 mo. Results showed that in the absence of light (i.e., in the absence of cyanobacteria) C. nucula undergo metabolic collapse and thiol depletion. In contrast, P. ficiformis activates heterotrophic metabolism and mechanisms which balance the loss of cell reducing power. This suggests that cyanobacteria effectively participate in controlling the redox potential of the host cells by the transfer of reducing equivalents. Only P. ficiformis is capable of counteracting, by means of heterotrophic metabolism, the loss of the contribution from symbionts which is caused by dark conditions. This explains the differences in the ecological requirements of the two species. Because cyanobacterial symbionts release fixed carbon in the form of glycerol and other small organic phosphate (Wilkinson 1979), a model based on the glycerol 3-phosphate shuttle (typically occurring in chloroplasts and mitochondria) is suggested. The mechanism proposed appears to be an ancient biochemical adaptation which arose among ancestral symbiotic systems, and further developed in the relationships between endosymbiotic organelles and cytoplasm.

Three-dimensional chitin-based scaffolds from Verongida sponges (Demospongiae: Porifera). Part II: Biomimetic potential and applications

In order to evaluate the biomedical potential of three-dimensional chitinous scaffolds of poriferan origin, chondrocyte culturing experiments were performed. It was shown for the first time that freshly isolated chondrocytes attached well to the chitin scaffold and synthesized an extracellular matrix similar to that found in other cartilage tissue engineering constructs. Chitin scaffolds also supported deposition of a proteoglycan-rich extracellular matrix of chondrocytes seeded bioconstructs in an in vivo environment. We suggest that chitin sponge scaffolds, apart from the demonstrated biomedical applications, are highly optimized structures for use as filtering systems, templates for biomineralization as well as metallization in order to produce catalysts.

Structural Characterization of Siliceous Spicules from Marine Sponges

Siliceous sponges, one of the few animal groups involved in a biosilicification process, deposit hydrated silica in discrete skeletal elements called spicules. A multidisciplinary analysis of the structural features of the protein axial filaments inside the spicules of a number of marine sponges, belonging to two different classes (Demospongiae and Hexactinellida), is presented, together with a preliminary analysis of the biosilicification process. The study was carried out by a unique combination of techniques: fiber diffraction using synchrotron radiation, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), Fourier transform infrared spectroscopy (FTIR), and molecular modeling. From a phylogenetic point of view, the main result is the structural difference between the dimension and packing of the protein units in the spicule filaments of the Demospongiae and the Hexactinellida species. Models of the protein organization in the spicule axial filaments, consistent with the various experimental evidences, are given. The three different species of demosponges analyzed have similar general structural features, but they differ in the degree of order. The structural information on the spicule axial filaments can help shed some light on the still unknown molecular mechanisms controlling biosilicification.

Parasitic diatoms inside antarctic sponges.

Antarctic sponges may host large populations of planktonic and benthic diatoms. After settling on the sponge, these diatoms enter its body through pinacocytes (1) and form, there, large mono- or pauci-specific assemblages. Yet the total amount of carbohydrates in the invaded sponge tissue is inversely correlated with that of chlorophyll-a. We suggest, therefore, that endobiont diatoms utilize the products of the metabolism of their host as an energy source. This is the first evidence indicating that an endobiotic autotrophic organism may parasitize its animal host. Moreover, this unusual symbiotic behavior could be a successful strategy that allows the diatom to survive in darkness.

Characteristics of the mesophotic megabenthic assemblages of the Vercelli Seamount (North Tyrrhenian Sea)

The biodiversity of the megabenthic assemblages of the mesophotic zone of a Tyrrhenian seamount (Vercelli Seamount) is described using Remotely Operated Vehicle (ROV) video imaging from 100 m depth to the top of the mount around 61 m depth. This pinnacle hosts a rich coralligenous community characterized by three different assemblages: (i) the top shows a dense covering of the kelp Laminaria rodriguezii; (ii) the southern side biocoenosis is mainly dominated by the octocorals Paramuricea clavata and Eunicella cavolinii; while (iii) the northern side of the seamount assemblage is colonized by active filter-feeding organisms such as sponges (sometimes covering 100% of the surface) with numerous colonies of the ascidian Diazona violacea, and the polychaete Sabella pavonina. This study highlights, also for a Mediterranean seamount, the potential role of an isolated rocky peak penetrating the euphotic zone, to work as an aggregating structure, hosting abundant benthic communities dominated by suspension feeders, whose distribution may vary in accordance to the geomorphology of the area and the different local hydrodynamic conditions.

Biogeographic traits and checklist of Antarctic demosponges

SummaryThe biogeography of Antarctic demosponges has been studied by dividing Antarctic and circumantarctic areas into geographic entities, and then assigning to these entities all recorded species according to literature reports. Correspondence analysis ordination based on the presence or absence of species shows the existence of a distinct Antarctic Faunistic Complex (AFC), including continental Antarctica, most of the Antarctic and circumantarctic islands and the Magellan area. Such a result has enabled us to drawup a checklist of 352 Antarctic demosponge species. Investigation of within-AFC patterns indicates that the continent is a highly homogeneous area, establishing closer relationships with the Scotia Arc and to a lesser extent with the Magellan region. The AFC has low specific affinities with the other circumantarctic regions (South Africa, temperate Australia and New Zealand), whereas at the generic level relationships appear more pronounced. This biogeographic pattern may lead us to suppose a common Gondwanian origin for Antarctic and circumantarctic sponge faunas, followed by differentiation due to Gondwana fragmentation. Antarctica moved towards polar latitudes and became progressively isolated, only maintaining active interchanges with South America. Climatic changes possibly induced intense processes of speciation in the Antarctic demosponge fauna, thus contributing to its differentiation.

Body Polarity and Mineral Selectivity in the Demosponge Chondrosia reniformis

The skeleton of the common Mediterranean demosponge Chondrosia reniformis lacks endogenous spicules; but exogenous siliceous material is selectively incorporated into its collagenous ectosome, strengthening this layer. Nevertheless, the settling of sponge buds during asexual reproduction necessitates an active incorporation of the calcareous substratum through the sponge lower ectosome. This fact suggests the presence of a polarity in the sponge, with the lower surface selecting primarily carbonates, and the upper surface selecting exclusively silicates and quartz. Our observations under experimental conditions showed that the strong selectivity of the upper ectosome is realized only when the sponge is fixed to the substratum; if detached, the sponge incorporates both quartz and carbonates. In laboratory experiments, the incapacity of both kinds of ectosome to regenerate into a new complete sponge suggests that this polarity arises early in ontogeny.

Population dynamics of Eudendrium glomeratum (Cnidaria: Anthomedusae) on the Portofino Promontory (Ligurian Sea)

Eudendrium glomeratum Picard, in the Ligurian Sea, is one of the major components of hard-bottom sessile zoobenthos in the cold season. It settles mainly between 10 and 40 m depth, forming a seasonal facies. The presence of E. glomeratum has been evaluated by measuring in situ the height of the colonies present within a standard surface of 1 m2. Observations were carried out every other week for a whole year. The height of the colonies was correlated with their biomass (wet weight) and trophic functionality (number of polyps). The quantitative evaluation of the population shows that the situation is stable, with almost identical values at the extremes of the observed yearly time series. The species is present from October to April–May, and it is absent in the summer. The formation and disappearance of the E. glomeratum population are sudden. The colonies are sexually mature from their appearance in October to December–January. Different categories of colonies are recognizable; and are essentially referable to two groups: (1) colonies deriving from regeneration of colonies present in the previous year (45%); (2) colonies deriving from planula settlement (43%). A third group (12%) is of uncertain origin and may belong to either of the abovementioned categories. Mortality is 60% in the first group, and 82% in the second one. By “dead colonies” is meant those which do not reappear after a yearly cycle.