Bacterial Consortium of Millepora dichotoma Exhibiting Unusual Multifocal Lesion Event in the Gulf of Eilat, Red Sea

Colonies of the hydrocoral Millepora dichotoma along the Gulf of Eilat are exhibiting unusual tissue lesions in the form of white spots. The emergence and rapid establishment of these multifocal tissue lesions was the first of its kind reported in this region. A characterization of this morphological anomaly revealed bleached tissues with a significant presence of bacteria in the tissue lesion area. To ascertain possible differences in microbial biota between the lesion area and non-affected tissues, we characterized the bacterial diversity in the two areas of these hydrocorals. Both culture-independent (molecular) and culture-dependent assays showed a shift in bacterial community structure between the healthy and affected tissues. Several 16S rRNA gene sequences retrieved from the affected tissues matched sequences of bacterial clones belonging to Alphaproteobacteria and Bacteroidetes members previously associated with various diseases in scleractinian corals.     

Phosphorylation of Parkin by the cyclin-dependent kinase 5 at the linker region modulates its ubiquitin-ligase activity and aggregation

Mutations in Parkin are responsible for a large percentage of autosomal recessive juvenile parkinsonism cases. Parkin displays ubiquitin-ligase activity and protects against cell death promoted by several insults. Therefore, regulation of Parkin activities is important for understanding the dopaminergic cell death observed in Parkinson disease. We now report that cyclin-dependent kinase 5 (Cdk5) phosphorylates Parkin both in vitro and in vivo. We found that highly specific Cdk5 inhibitors and a dominant negative Cdk5 construct inhibited Parkin phosphorylation, suggesting that a significant portion of Parkin is phosphorylated by Cdk5. Parkin interacts with Cdk5 as observed by co-immunoprecipitation experiments of transfected cells and rat brains. Phosphorylation by Cdk5 decreased the auto-ubiquitylation of Parkin both in vitro and in vivo. We identified Ser-131 located at the linker region of Parkin as the major Cdk5 phosphorylation site. The Cdk5 phosphorylation-deficient S131A Parkin mutant displayed a higher auto-ubiquitylation level and increased ubiquitylation activity toward its substrates synphilin-1 and p38. Additionally, the S131A Parkin mutant more significantly accumulated into inclusions in human dopaminergic cells when compared with the wild-type Parkin. Furthermore, S131A Parkin mutant increased the formation of synphilin-1/alpha-synuclein inclusions, suggesting that the levels of Parkin phosphorylation and ubiquitylation may modulate the formation of inclusion bodies relevant to the disease. The data indicate that Cdk5 is a new regulator of the Parkin ubiquitin-ligase activity and modulates its ability to accumulate into and modify inclusions. Phosphorylation by Cdk5 may contribute to the accumulation of toxic Parkin substrates and decrease the ability of dopaminergic cells to cope with toxic insults in Parkinson disease.     

Characterization of black band disease in Red Sea stony corals

Microbial communities associated with black band disease (BBD) in massive stony corals from the Northern Red Sea (Eilat) were examined for the first time using molecular tools and microscopy. A high microbial diversity was revealed in the affected tissue in comparison with the healthy area of the same colony. Microscopy revealed the penetration of cyanobacteria into the coral mesoglea and adjacent tissues. Cyanobacterial sequences from Red Sea BBD-affected corals formed a cluster with sequences previously identified from black band and red band diseased corals from the Indo-Pacific and Caribbean. In addition, 11 sequences belonging to the genus Vibrio were retrieved. This group was previously documented as pathogenic to corals. Sulfate-reducing bacteria, a group known to be associated with BBD and produce toxic sulfide, were studied using specific primers for the amplification of the dissimilatory sulfite reductase gene (dsrA). This technique facilitated and improved the resolution of the study of diversity of this group. All the sequences obtained were closely related to sequences of the genus Desulfovibrio and 46% showed high homology to Desulfovibrio desulfuricans. The complex nature of BBD and the lack of success in isolating a single causative agent suggest that BBD may be considered a polymicrobial disease.     

Heparanase uptake is mediated by cell membrane heparan sulfate proteoglycans

Heparanase is a mammalian endoglycosidase that degrades heparan sulfate (HS) at specific intrachain sites, an activity that is strongly implicated in cell dissemination associated with metastasis and inflammation. In addition to its structural role in extracellular matrix assembly and integrity, HS sequesters a multitude of polypeptides that reside in the extracellular matrix as a reservoir. A variety of growth factors, cytokines, chemokines, and enzymes can be released by heparanase activity and profoundly affect cell and tissue function. Thus, heparanase bioavailability, accessibility, and activity should be kept tightly regulated. We provide evidence that HS is not only a substrate for, but also a regulator of, heparanase. Addition of heparin or xylosides to cell cultures resulted in a pronounced accumulation of, heparanase in the culture medium, whereas sodium chlorate had no such effect. Moreover, cellular uptake of heparanase was markedly reduced in HS-deficient CHO-745 mutant cells, heparan sulfate proteoglycan-deficient HT-29 colon cancer cells, and heparinase-treated cells. We also studied the heparanase biosynthetic route and found that the half-life of the active enzyme is approximately 30 h. This and previous localization studies suggest that heparanase resides in the endosomal/lysosomal compartment for a relatively long period of time and is likely to play a role in the normal turnover of HS. Co-localization studies and cell fractionation following heparanase addition have identified syndecan family members as candidate molecules responsible for heparanase uptake, providing an efficient mechanism that limits extracellular accumulation and function of heparanase.     

An in situ method for cultivating microorganisms using a double encapsulation technique

The lack of cultured microorganisms represents a bottleneck for advancement in microbiology. The development of novel culturing techniques is, therefore, a crucial step in our understanding of microbial diversity in general, and the role of such diversity in the environment, in particular. This study presents an innovative method for cultivating microorganisms by encapsulating them within agar spheres, which are then encased in a polysulfonic polymeric membrane and incubated in a simulated or natural environment. This method stimulates growth of the entrapped microorganisms by allowing them access to essential nutrients and cues from the environment. It allows for the discovery of microorganisms from dilutions that are 10–100-fold greater than possible with conventional plating techniques. Analysis of microorganisms grown in such spheres incubated in and on a number of different substrates yielded numerous novel ribotypes. For example, spheres incubated on the mucus surface of a Fungiid coral yielded numerous ribotypes, with only 50% sharing similarity (85–96%) to previously identified microorganisms. This suggests that many of the species represent novel ribotypes. Hence, the technique reported here advances our ability to retrieve and successfully culture microorganisms and provides an innovative tool to access unknown microbial diversity.     

Population dynamics of zooxanthellae during a bacterial bleaching event

Each summer 80–90% of the colonies of Oculina patagonica undergo bleaching off the Mediterranean coast of Israel. To investigate fluctuations through a yearly bleaching cycle, monthly measurements of zooxanthella density, mitotic index and chlorophyll-a concentration were conducted. Results showed (1) a significant negative correlation between sea surface temperature (SST) and zooxanthella density; (2) both significantly lower zooxanthella mitotic index and higher chlorophyll-a per zooxanthella content during the bleaching season compared with the non-bleaching period; (3) prior to bleaching, a lag between the peak of zooxanthella density and chlorophyll-a concentration followed by a similar lag during recovery. Zooxanthella density declined significantly between March and May while chlorophyll-a concentration peaked in April, and then declined. Zooxanthella density increased significantly in November while chlorophyll-a concentration increased significantly in January. We conclude that during bacterial bleaching events, zooxanthellae are severely damaged. However, by the time of the following bleaching event the coral tissues regain their “normal” (pre-bleaching) zooxanthella population density.     

Spectral Diversity and Regulation of Coral Fluorescence in a Mesophotic Reef Habitat in the Red Sea

The phenomenon of coral fluorescence in mesophotic reefs, although well described for shallow waters, remains largely unstudied. We found that representatives of many scleractinian species are brightly fluorescent at depths of 50–60 m at the Interuniversity Institute for Marine Sciences (IUI) reef in Eilat, Israel. Some of these fluorescent species have distribution maxima at mesophotic depths (40–100 m). Several individuals from these depths displayed yellow or orange-red fluorescence, the latter being essentially absent in corals from the shallowest parts of this reef. We demonstrate experimentally that in some cases the production of fluorescent pigments is independent of the exposure to light; while in others, the fluorescence signature is altered or lost when the animals are kept in darkness. Furthermore, we show that green-to-red photoconversion of fluorescent pigments mediated by short-wavelength light can occur also at depths where ultraviolet wavelengths are absent from the underwater light field. Intraspecific colour polymorphisms regarding the colour of the tissue fluorescence, common among shallow water corals, were also observed for mesophotic species. Our results suggest that fluorescent pigments in mesophotic reefs fulfil a distinct biological function and offer promising application potential for coral-reef monitoring and biomedical imaging.     

Heat-Stress and Light-Stress Induce Different Cellular Pathologies in the Symbiotic Dinoflagellate during Coral Bleaching

Coral bleaching is a significant contributor to the worldwide degradation of coral reefs and is indicative of the termination of symbiosis between the coral host and its symbiotic algae (dinoflagellate; Symbiodinium sp. complex), usually by expulsion or xenophagy (symbiophagy) of its dinoflagellates. Herein, we provide evidence that during the earliest stages of environmentally induced bleaching, heat stress and light stress generate distinctly different pathomorphological changes in the chloroplasts, while a combined heat- and light-stress exposure induces both pathomorphologies; suggesting that these stressors act on the dinoflagellate by different mechanisms. Within the first 48 hours of a heat stress (32°C) under low-light conditions, heat stress induced decomposition of thylakoid structures before observation of extensive oxidative damage; thus it is the disorganization of the thylakoids that creates the conditions allowing photo-oxidative-stress. Conversely, during the first 48 hours of a light stress (2007 µmoles m⁻² s⁻¹ PAR) at 25°C, condensation or fusion of multiple thylakoid lamellae occurred coincidently with levels of oxidative damage products, implying that photo-oxidative stress causes the structural membrane damage within the chloroplasts. Exposure to combined heat- and light-stresses induced both pathomorphologies, confirming that these stressors acted on the dinoflagellate via different mechanisms. Within 72 hours of exposure to heat and/or light stresses, homeostatic processes (e.g., heat-shock protein and anti-oxidant enzyme response) were evident in the remaining intact dinoflagellates, regardless of the initiating stressor. Understanding the sequence of events during bleaching when triggered by different environmental stressors is important for predicting both severity and consequences of coral bleaching.