Coral reefs are declining worldwide due to increased incidence of climate-induced coral bleaching, which will have widespread biodiversity and economic impacts. A simple method to measure the sub-bleaching level of heat-light stress experienced by corals would greatly inform reef management practices by making it possible to assess the distribution of bleaching risks among individual reef sites. Gene expression analysis based on quantitative PCR (qPCR) can be used as a diagnostic tool to determine coral condition in situ. We evaluated the expression of 13 candidate genes during heat-light stress in a common Caribbean coral Porites astreoides, and observed strong and consistent changes in gene expression in two independent experiments. Furthermore, we found that the apparent return to baseline expression levels during a recovery phase was rapid, despite visible signs of colony bleaching. We show that the response to acute heat-light stress in P. astreoides can be monitored by measuring the difference in expression of only two genes: Hsp16 and actin. We demonstrate that this assay discriminates between corals sampled from two field sites experiencing different temperatures. We also show that the assay is applicable to an Indo-Pacific congener, P. lobata, and therefore could potentially be used to diagnose acute heat-light stress on coral reefs worldwide.

Sponges are abundant, diverse and functionally important components of aquatic biotopes with crucial associations for many reef fish and invertebrates. Sponges have strict temperature optima, and mass mortality events have occurred after unusually high temperatures. To assess how sponges may adapt to thermal stress associated with a changing climate, we applied gene expression profiling to both stages of their bipartite life cycles. Adult Rhopaloeides odorabile are highly sensitive to thermal stress (32 °C), yet their larvae can withstand temperatures up to 36 °C. Here, we reveal the molecular mechanisms that underpin these contrasting thermal tolerances, which may provide sponges with a means to successfully disperse into cooler waters. Heat shock protein 70 was induced by increasing temperature in adult sponges, and genes involved in important biological functions including cytoskeleton rearrangement, signal transduction, protein synthesis/degradation, oxidative stress and detoxification were all negatively correlated with temperature. Conversely, gene expression in larvae was not significantly affected until 36 °C when a stress response involving extremely rapid activation of heat shock proteins occurred. This study provides the first transcriptomic assessment of thermal stress on both life history stages of a marine invertebrate facilitating better predictions of the long-term consequences of climate change for sponge population dynamics.

In light of increasing sea surface temperatures, quantifying the expression of stressinducible genes in coastal organisms is imperative to identify early biomarkers of thermal stress. In the present study we developed a quantitative PCR (qPCR) assay to test the molecular response to heat stress in the Great Barrier Reef sponge Rhopaloeides odorabile. Suitable reference genes (coding for α-tubulin, 28S rRNA and ubiquitin) were identified among 5 candidates and then used to normalise expression of target genes (actin-related protein, calmodulin, ferritin, ubiquitin-conjugating enzyme, heat shock protein 90 [Hsp90] and heat shock protein 40 [Hsp40]) in samples exposed to high temperatures (31 and 32°C) for 1, 3, 14 and 15 d. A rapid down-regulation of most genes (actinrelated protein, ferritin, calmodulin and Hsp90) was observed at both temperatures within 24 h, indicating an initial shut-down of the sponge's molecular systems in response to thermal stress. The increased expression of Hsp40 and Hsp90 in sponges at 32°C after 1 and 3 d respectively indicates an activation of the heat shock response system and is consistent with their role as chaperones for directing degraded proteins to proteolysis, this last process being sustained by an induction of the ubiquitin-conjugating enzyme gene at this temperature. While sponges kept at 32°C only survived for the first 3 d, none of the genes in sponges kept at 31°C were significantly different from those in the 27°C controls after 14 d. This indicates a very strict thermal threshold for R. odorabile between 31 and 32°C and is consistent with previous findings based on sponge necrosis and symbiotic disruptions in this species.KEY WORDS: qPCR · Quantitative PCR · Thermal stress · Porifera · Great Barrier Reef Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 431: [97][98][99][100][101][102][103][104][105] 2011 tance of Porifera, the effect of thermal stress on sponges has rarely been investigated, particularly at the molecular level. The few studies published on this topic include a thermal-stress experiment in which Western blotting was utilised to show that the marine sponge Suberites domuncula ex presses a 45 kDa polypeptide after heat treatment (Bachinski et al. 1997). Moreover, a drop in trehalose (a disaccharide that can protect yeast from temperature stress as shown by Hottiger et al. 1987 andEleutherio et al. 1993), a reduction in the activity of the detoxifying and antioxidant enzyme glutathione-S-transferase (GST) and a concomitant decrease of its substrate glutathione (GSH) were recorded in the same specimens. In heatand cold-stressed Geodia cydonium, an in creased transcription of the heat shock protein 70 (Hsp70) gene and a reduction of the Rab GDP dissociation inhibitor (GDI) mRNA (a key element in the intracellular traffic system) were observed using Northern blotting (Krasko et al. 1997). These findings indicate the presence of active heat-stress protection mechanisms in sponges at the cellular leve...

Bacteria were isolated seasonally from the Mediterranean sponges Chondrilla nucula and Petrosia ficiformis and screened for antibacterial activities. Selected isolates were taxonomically identified by 16S rRNA gene sequencing. A total of 416 different bacterial strains were isolated, 60 (14.4%) of which displayed variable degrees of antimicrobial activity. Of the bioactive strains, 58.3% were able to inhibit Staphylococcus aureus, 6.7% were active against Bacillus subtilis, 11.7% against both Enterococcus faecalis and Escherichia coli, 38.3% against Pseudoalteromonas atlantica and 33.3% against Pseudomonas elongata. 16S rRNA gene sequence analysis showed that 2 isolates, 1 from seawater samples and 1 from P. ficiformis, were most closely related to Bacillus subtilis (99% similarity) and that another isolate from P. ficiformis was most closely related to a previously described sponge-associated Alphaproteobacterium NW001 (98% similarity). Two isolates from C. nucula were most closely related to Brachybacterium paraconglomeratum (99% similarity) and Shewanella algae (89% similarity). The high percentage of bioactive isolates derived from the 2 sponges suggests that marine microorganisms, whether animal-associated or planktonic, are promising sources for drug discovery.KEY WORDS: Antimicrobial activity · Associated bacteria · Chondrilla nucula · Petrosia ficiformis · Porifera · 16S rRNA Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 49: [157][158][159][160][161][162][163] 2007 compounds of interest are found only in traces and harvesting in the field poses ethical and operational constraints.We focus here on the isolation of bacteria from 2 Mediterranean sponges. Chondrilla nucula Schmidt 1862 (Demospongiae, Chondrosida) is a thick encrusting sponge that forms large patches of interconnected clones on well-lit substrata. It occurs from the sea surface to ~30 m depth. In addition to populations of Synechococcus (Cyanobacteria) in the light-exposed sponge surface layer, there are extracellular heterotrophic bacteria in the mesohyl matrix. The heterotrophs are sometimes enclosed within bacteriocytes (Usher et al. 2004). The bacterial community associated with C. nucula was recently characterized by 16S rDNA-based methods ). Interestingly, 79% of all C. nucula-derived phylotypes were most closely related to other sponge-specific microbial lineages, which reflects the highly specific nature of the microbial community associated with marine 'bacteriosponges . Cytotoxic and deterrent activities have been demonstrated in Mediterranean and Caribbean C. nucula specimens (see references in Milanese et al. 2003).Petrosia ficiformis (Poiret 1789) (Demospongiae, Haplosclerida) is a massive sponge living on hard substrata to ~50 m depth. The color of the sponge can be either dark-violet or white depending on the presence or absence of pigmented, symbiotic Synechococcus (Usher et al. 2004). Cyanobacteria symbiotic in P. ficiformis play a metabolic role and are also invo...