Theonellamides J and K and 5-cis-Apoa-theopalauamide, Bicyclic Glycopeptides of the Red Sea Sponge Theonella swinhoei

Theonella swinhoei is a fairly common inhabitant of reefs throughout the Indian and Pacific Oceans. Metabolomic analyses of samples of T. swinhoei collected in different depths in the Gulf of Aqaba revealed two chemotypes differing in the profiles of the theonellamides they produce, some of which seem to be unknown. Driven by this finding, we examined a sample of T. swinhoei collected more than 40 years ago in the southern part of the Gulf of Aqaba. Large-scale extract of this sample yielded four theonellamides, the known theopalauamide (4), as the major component, and three new metabolites, theonellamide J (1), 5-cis-Apoa-theopalauamide (2), and theonellamide K (3), as the minor components. The planar structure of these complex cyclic glycopeptides was elucidated by combination of 1D and 2D NMR techniques and HRESIMS. The absolute configuration of the amino acids was established by Marfey’s and advanced Marfey’s methods, and the absolute configuration of its galactose unit using “Tanaka’s method” for monosaccharides. The biological activity of the pure compounds was tested for antibacterial activity and for cytotoxicity to HTC-116 cell line. The compounds presented significant cytotoxicity against the HTC-116 cell line, illuminating the importance of the Apoa subunit for the activity.

Coral Bleaching Resistance vs Susceptibility: The Role of Antioxidant Activity in Symbiotic Dinoflagellates

<p>Coral bleaching, the loss of symbiotic dinoflagellate algae (genus Symbiodinium) and/or photosynthetic algal pigments from their coral host has become a regular occurrence in the last few decades due to increasing seawater temperatures. A key consideration in bleaching susceptibility is the symbiotic alga‘s physiology and its capacity to deal with abiotic stress; oxidative stress is of particular interest given that this can arise from thermally induced photosynthetic dysfunction. The aim of this study was to compare the effects of thermal and oxidative stress on the photosynthetic performance of a range of Symbiodinium clades and types (i.e. sub-clades) in different states of symbiosis (in hospite, freshly isolated and in culture). Whether the responses to these two stressors are related was investigated; in particular, it was hypothesised that more thermally sensitive types would be more sensitive to oxidative stress. Furthermore, the study aimed to elucidate the role of antioxidants in the observed stress responses. The specific objectives were 1) to establish whether different types of cultured Symbiodinium have dissimilar sensitivities to oxidative stress, induced by hydrogen peroxide (H₂O₂), and whether these are related to their thermal sensitivities; 2) measure the activity and relative amounts of specific reactive oxygen species (ROS) in different types of cultured Symbiodinium in response to thermal and oxidative stress induced by H₂O₂; 3) measure total antioxidant activity in different cultured Symbiodinium types when under oxidative stress; and 4) compare and contrast the responses of different Symbiodinium types to thermal and oxidative stress when in hospite (i.e. in corals) and freshly isolated. In this study, I showed that different Symbiodinium clades and types can differ widely in their responses to both thermal and oxidative stress. This was indicated by photosynthetic performance measured by chlorophyll fluorescence, and differences in the quantity of specific ROS measured via fluorescent probes and flow cytometry. For instance, when adding H₂O₂ to Symbiodinium F1, originally from Hawaii, a decrease of > 99% in maximum quantum yield (Fv/Fm) was displayed, while there was no change in Fv/Fm in the temperate Symbiodinium A1, freshly isolated from the anemone Anthopleura aureoradiata from New Zealand. When comparing the difference in ROS production between the control (26 °C) and a thermal stress treatment (35 °C), type E1 from Okinawa showed no difference in any of the measured ROS. In contrast, a different A1 type from the Gulf of Aqaba displayed an increase in the overall production of ROS, and more specifically in the production of superoxide. Symbiodinium types also displayed differential oxidative stress resistance, which was apparent from their antioxidant activities; in particular, total antioxidant capacity was measured by the ferric reducing antioxidant potential (FRAP) and cellular antioxidant activity (CAA) assays. For example, the aforementioned Symbiodinium types, A1 from the Gulf of Aqaba and F1, increased their antioxidant activities with increasing H₂O₂ concentrations. Meanwhile, type E1 displayed higher baseline levels of antioxidants in comparison to the other two types (A1, F1), which then decreased with increasing H₂O₂. Specific activities of superoxide dismutase and ascorbate peroxidase were also measured. Stress susceptibility appears to be related both to Symbiodinium type and geographic origin, but greater sensitivity to thermal stress did not necessarily correlate with greater susceptibility to oxidative stress. The exact relationship between thermal and oxidative sensitivities in Symbiodinium spp. remains elusive, but it is suggested that different types might follow different strategies for dealing with stress. I propose that some Symbiodinium types rely more on photo-protection when exposed to thermal stress (and hence cope less with oxidative stress), while other types depend more on antioxidants and oxidative stress resistance. The latter might be the better strategy for types from more variable environments, such as higher latitude reefs or intertidal regions, where potentially stressful conditions may be encountered more frequently. This study gives new insights into the variability of stress responses in the genus Symbiodinium, and the complex relationship between thermal and oxidative stress. The implications of these findings for coral bleaching susceptibility and the biogeographic distribution of different Symbiodinium types are discussed.</p>

Coral Bleaching Resistance vs Susceptibility: The Role of Antioxidant Activity in Symbiotic Dinoflagellates

<p>Coral bleaching, the loss of symbiotic dinoflagellate algae (genus Symbiodinium) and/or photosynthetic algal pigments from their coral host has become a regular occurrence in the last few decades due to increasing seawater temperatures. A key consideration in bleaching susceptibility is the symbiotic alga‘s physiology and its capacity to deal with abiotic stress; oxidative stress is of particular interest given that this can arise from thermally induced photosynthetic dysfunction. The aim of this study was to compare the effects of thermal and oxidative stress on the photosynthetic performance of a range of Symbiodinium clades and types (i.e. sub-clades) in different states of symbiosis (in hospite, freshly isolated and in culture). Whether the responses to these two stressors are related was investigated; in particular, it was hypothesised that more thermally sensitive types would be more sensitive to oxidative stress. Furthermore, the study aimed to elucidate the role of antioxidants in the observed stress responses. The specific objectives were 1) to establish whether different types of cultured Symbiodinium have dissimilar sensitivities to oxidative stress, induced by hydrogen peroxide (H₂O₂), and whether these are related to their thermal sensitivities; 2) measure the activity and relative amounts of specific reactive oxygen species (ROS) in different types of cultured Symbiodinium in response to thermal and oxidative stress induced by H₂O₂; 3) measure total antioxidant activity in different cultured Symbiodinium types when under oxidative stress; and 4) compare and contrast the responses of different Symbiodinium types to thermal and oxidative stress when in hospite (i.e. in corals) and freshly isolated. In this study, I showed that different Symbiodinium clades and types can differ widely in their responses to both thermal and oxidative stress. This was indicated by photosynthetic performance measured by chlorophyll fluorescence, and differences in the quantity of specific ROS measured via fluorescent probes and flow cytometry. For instance, when adding H₂O₂ to Symbiodinium F1, originally from Hawaii, a decrease of > 99% in maximum quantum yield (Fv/Fm) was displayed, while there was no change in Fv/Fm in the temperate Symbiodinium A1, freshly isolated from the anemone Anthopleura aureoradiata from New Zealand. When comparing the difference in ROS production between the control (26 °C) and a thermal stress treatment (35 °C), type E1 from Okinawa showed no difference in any of the measured ROS. In contrast, a different A1 type from the Gulf of Aqaba displayed an increase in the overall production of ROS, and more specifically in the production of superoxide. Symbiodinium types also displayed differential oxidative stress resistance, which was apparent from their antioxidant activities; in particular, total antioxidant capacity was measured by the ferric reducing antioxidant potential (FRAP) and cellular antioxidant activity (CAA) assays. For example, the aforementioned Symbiodinium types, A1 from the Gulf of Aqaba and F1, increased their antioxidant activities with increasing H₂O₂ concentrations. Meanwhile, type E1 displayed higher baseline levels of antioxidants in comparison to the other two types (A1, F1), which then decreased with increasing H₂O₂. Specific activities of superoxide dismutase and ascorbate peroxidase were also measured. Stress susceptibility appears to be related both to Symbiodinium type and geographic origin, but greater sensitivity to thermal stress did not necessarily correlate with greater susceptibility to oxidative stress. The exact relationship between thermal and oxidative sensitivities in Symbiodinium spp. remains elusive, but it is suggested that different types might follow different strategies for dealing with stress. I propose that some Symbiodinium types rely more on photo-protection when exposed to thermal stress (and hence cope less with oxidative stress), while other types depend more on antioxidants and oxidative stress resistance. The latter might be the better strategy for types from more variable environments, such as higher latitude reefs or intertidal regions, where potentially stressful conditions may be encountered more frequently. This study gives new insights into the variability of stress responses in the genus Symbiodinium, and the complex relationship between thermal and oxidative stress. The implications of these findings for coral bleaching susceptibility and the biogeographic distribution of different Symbiodinium types are discussed.</p>

Una lettera di Paolo Bajnotti a Cristoforo Negri nel contesto dell’esplorazione del Mar Morto nel XIX secolo

A letter in the archives of the Italian Geographical Society in which Paolo Bajnotti, an italian diplomat who had resided in Egypt, informs Cristoforo Negri about his trip to Palestine in 1869, before moving to Galaz for a new assignment, and about how he visited the Dead Sea thanks to the guidance of a Franciscan scholar who reported that he had personally observed that over the last ten years the level of the Dead Sea had dropped by about 95 cm, provides the opportunity for a historical overview of the exploration of the Jordan Valley from Lake Tiberias to the Gulf of Aqaba during the 19th century. What might seem to be a mere curiosity is in fact part of a very significant issue that was controversial among the geographers and cartographers of the time, as is clearly shown in Negri’s speech at the meeting of the Società Geografica Italiana on March 13th 1870. The level of the Dead Sea and the level of the Sea of Galilee, the resulting difference in height that the River Jordan has to cover with a significant average gradient, the lack of a rise in the level of the Dead Sea despite the absence of an estuary were questions that in the mid-19th century were still waiting for an answer supported by scientific data and free of pious or pseudo-scientific overtones. A numerous series of expeditions - some improvised, others well organized - gave some answers to these issues, removing any doubt and establishing that the entire hydrologic basin was significantly below the level of the Mediterranean, that the Jordan did not have a strong slope because it was very meandering, and that the Dead Sea’s level was regulated by the strong amount of evaporation that occurred throughout the year.

Management effectiveness suggests a role in structuring herbivorous fish communities in Sinai marine protected areas, Gulf of Aqaba

Herbivorous reef fishes are critically important for maintaining the health and resilience of coral reefs. In the Egyptian Gulf of Aqaba (GoA), many of these herbivores are important fishery targets and little is known about their population size structure and biomass patterns. Here, we conduct a large-scale (~250 km of coastline) assessment of the status of herbivorous fish populations along a fishing pressure gradient at 30 sites and eight regions in the GoA. These regions are subjected to three levels of fishing and protection, ranging from almost no fishing (No take, NT), and moderately fished (via Gear restriction, GR) to heavily fished (Open access, OA). We found that the NT fishery reserve was the most effective to maintain herbivorous fish size, biomass, and richness across all functional groups, though numerical density was not. Total herbivore biomass was 4.3 and 2.8 times higher on NT reefs and GR reefs, respectively than on OA reefs. Among GoA regions, only Ras Mohammed and Sharm El-Sheikh (unfished), and Nabq (fished) met the global mean herbivore biomass target of ~30 kg/500 m2. Our work also highlights three important results regarding the impacts of fishing and fisheries management on herbivorous fish populations: (i) size structure was heavily skewed toward smaller individuals, with fishes less than (20 cm) accounting for 81.1% of the population in heavily fished OA reefs vs. 52.8% at unfished NT reefs, (ii) biomass of larger herbivore individuals (>35 cm) accounting for less than 1% of the total biomass in OA reefs vs. 37% at NT reefs, and (iii) large-bodied target species, Cetoscarus bicolor, Naso unicorn, and Kyphosus spp., accounting for 15.9% of the total biomass at NT reefs on average, while they were virtually absent from OA reefs. Collectively, these findings suggest that many principal fisheries species in the central northern regions of the GoA have been overexploited, which in turn can lead to reef degradation. Therefore, there is an urgent need to develop a participatory management approach and enforce restrictions on destructive fishing gear in order to promote recovery of herbivore biomass.