ORCID Profile
0000-0001-7685-6727
Current Organisations
Ben-Gurion University of the Negev
,
Achva Academic College
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Publisher: Springer Science and Business Media LLC
Date: 29-01-2012
DOI: 10.1007/S00248-011-0006-6
Abstract: Coral holobionts are densely populated with microorganisms that are essential for their well-being. Here we compared the ersity of the archaeal ammonia monooxygenase alpha subunit (amoA) gene from three coral genera, Acanthastrea sp., Favia sp., and Fungia granulosa, from the Gulf of Eilat, Red Sea. At 99% similarity, archaeal amoA from the three coral genera shared 71% of their cloned sequences, while the Favia and Acanthastrea presented a few genus-specific clones. In addition, the sequences retrieved in our s les displayed lower similarity to amoA sequences previously found in association with other coral species from different geographic regions. This finding suggests that the populations of ammonia-oxidizing archaea are less host-specific and more geographically dependent.
Publisher: Wiley
Date: 30-09-2008
DOI: 10.1111/J.1462-2920.2008.01718.X
Abstract: Diversity, distribution and genetic comparison of Archaea associated with the surface mucus of corals from three genera, namely Acanthastrea sp., Favia sp. and Fungia sp., from the Gulf of Eilat, Israel and from Heron Island, Australia were studied. Sequencing of the 16S rRNA gene of the coral-associated Archaea revealed dominance of Crenarchaeota (79%, on average). In this phylum, 87% of the sequences were similar (>or= 97%) to the Thermoprotei, with 76% of these being similar (>or= 97%) to the ammonium oxidizer, Nitrosopumilus maritimus. Most of the coral-associated euryarchaeotal sequences (69%) were related to marine group II, while other euryarchaeotal clades were found to be related to anaerobic methanotrophs (8%), anaerobic nitrate reducers (i.e. denitrification, 15%) and marine group III (8%). Most of the crenarchaeotal and euryarchaeotal coral-associated 16S rRNA gene sequences from Heron Island (61%) and from the Gulf of Eilat (71%) were closely related (>or= 97%) to sequences previously derived from corals from the Virgin Islands. Analysis of archaeal amoA sequences obtained from the fungiid coral, Fungia granulosa, ided into three clades, all related to archaeal sequences previously obtained from the marine environment. These sequences were distantly related to amoA sequences previously found in association with other coral species. Preliminary experiments suggest that there is active oxidation of ammonia to nitrite in the mucus of F. granulosa. Thus, coral-associated Archaea may contribute to nitrogen recycling in the holobiont, presumably by acting as a nutritional sink for excess ammonium trapped in the mucus layer, through nitrification and denitrification processes.
Publisher: Inter-Research Science Center
Date: 18-07-2006
DOI: 10.3354/MEPS317067
Publisher: Elsevier BV
Date: 09-2007
Publisher: Inter-Research Science Center
Date: 17-09-2015
DOI: 10.3354/DAO02911
Abstract: Changes of the black band disease (BBD)-associated microbial consortium on the surface of a Favia sp. coral colony were assessed in relation to the different disease phases. A number of highly active bacterial groups changed in numbers as the BBD disease signs changed. These included Gamma- and Epsilonproteobacteria, Bacteroidetes and Firmicutes groups. One cyanobacterium strain, BGP10_4ST (FJ210722), was constantly present in the disease interface and adjacent tissues of the affected corals, regardless of disease phase. The dynamics of the operational taxonomic units (OTUs) of this BBD-specific strain provide a marker regarding the disease phase. The disease's active phase is characterized by a wide dark band progressing along the tissue-skeleton interface and by numerous bacterial OTUs. Cyanobacterial OTUs decreased in numbers as the disease signs waned, perhaps opening a niche for additional microorganisms. Even when black band signs disappeared there was a consistent though low abundance of the BBD-specific cyanobacteria (BGP10_4ST), and the microbial community of the disease-skeleton interface remained surprisingly similar to the original band community. These results provide an indication that the persistence of even low numbers of this BBD-specific cyanobacterium in coral tissues during the non-active (or subclinical) state could facilitate reinitiation of BBD signs during the following summer. This may indicate that this bacterium is major constituent of the disease and that its persistence and ability to infiltrate the coral tissues may act to facilitate the assembly of the other BBD-specific groups of bacteria.
Publisher: Springer Science and Business Media LLC
Date: 08-07-2010
DOI: 10.1007/S00248-010-9718-2
Abstract: Universal 16S rRNA gene primers (8F and 518R) bearing inosine substitutions at either the 3'-ultimate or the 3'-ultimate and penultimate base positions were exploited for the first time to study the bacterial community associated with coral polymicrobial Black Band Disease (BBD). Inosine-modified universal primer pairs display some shifting in the composition of 16S rRNA gene libraries, as well as expanding the observed ersity of a BBD bacterial community at the family/class level. Possible explanations for the observed shifts are discussed. These results thus point to the need for adopting multiple approaches in designing 16S rRNA universal primers for PCR lification and subsequent construction of 16S rRNA gene libraries or pyrosequencing in the exploration of complex microbial communities.
Publisher: Oxford University Press (OUP)
Date: 12-2009
DOI: 10.1111/J.1574-6941.2009.00770.X
Abstract: Black Band Disease (BBD) is a well-described disease plaguing corals worldwide. It has been established that ecological and environmental stress factors contribute to the appearance and progression of the disease, believed to be caused by a erse microbial consortium. We have identified and characterized Vibrio sp. associated with BBD in Eilat reef corals using both culture-dependent and -independent methods. Direct s ling using 16S rRNA gene clone libraries showed seasonal dynamics in the ersity of BBD-associated Vibrios. In the two s ling periods, BBD-associated Vibrio clones showed similarities to different groups: October s les were similar to known pathogens, while December s les were similar to general aquatic Vibrio sp. Cultured bacterial isolates of Vibrio sp. were highly homologous (>or=99%) to previously documented BBD-associated bacteria from the Caribbean, Bahamas and Red Seas, and were similar to several known coral pathogens, such as Vibrio coralliilyticus. The proteolytic activity of Vibrio sp., as measured using casein- and azocasein-based assays, directly correlated with temperature elevation and peaked at 26-28 degrees C, with the microorganisms producing more proteases per bacterial cell or increasing the rate of proteolytic activity of the same proteases (potentially metalloproteases). This activity may promote coral tissue necrosis and aid in ensuing progression of the coral BBD.
Publisher: Inter-Research Science Center
Date: 16-11-2009
DOI: 10.3354/DAO02089
Abstract: Black band disease (BBD) is a widespread coral disease which mainly infects massive framework-building corals. BBD is believed to be caused by a consortium of microorganisms and may not result from the actions of a primary pathogen. The BBD microbial community is dominated, in terms of biomass, by filamentous cyanobacteria. Here we describe a cyanobacterial strain, designated BgP10_4S(T), cultured from a BBD-affected Favia sp. 25 degreesoal from the northern Red Sea (Gulf of Eilat, Israel). This dark-green pigmented cyanobacterium showed optimal growth at salinities of 5.0 to 5.5% (w/v), pH of 7 to 8 and cultivation temperatures of 25 0C. Morphological examination revealed cylindrical, unbranched trichomes with tapering and blunt cells at the ends which leave a thin mucilaginous trail as they glide. No sheath was evident under these conditions. Inclusion bodies and straight thylakoids were clearly discerned by transmission electron microscopy. Pigment analysis revealed absorption spectra for phycocyanin, carotenoid and chlorophyll a. The sequence of the 16S rRNA gene in this cyanobac(t)erium isolate showed high similarity (99%) to cyanobacterial sequences retrieved from BBD-affected corals from different geographical sites (i.e. the Caribbean Sea, Palau and the Red Sea). The BgP10_4ST strain is observed to be a persisten(t) component of the BBD mat of Faviid corals and may thus be an important agent in the disease etiology. On the basis (of its morphological, physiological and phylogenetic distinctiveness, strain BgP10_4ST represents a novel genus and species of Subsection III (formerly Oscillatoriales), for which the name Pseudoscillatoria coralii gen. nov., sp. nov. is proposed.
Publisher: Wiley
Date: 03-2010
DOI: 10.1111/J.1550-7408.2010.00469.X
Abstract: The surfaces of massive corals of the genus Favia from Eilat, Red Sea, and from Heron Island, Great Barrier Reef, are covered by a layer of eukaryotic microorganisms. These microorganisms are embedded in the coral mucus and tissue. In the Gulf of Eilat, the prevalence of corals covered by patches of eukaryotic microorganisms was positively correlated with a decrease in water temperatures (from 25-28 degrees C in the summer to 20-23 degrees C in winter). Comparisons carried out using transmission and scanning electron microscopy showed morphological similarities between the microorganisms from the two geographically distant reefs. The microorganisms found on and in the tissues were approximately 5-15 microm in diameter, surrounded by scales in their cell wall, contained a nucleus, and included unique auto-florescent coccoid bodies of approximately 1 mum. Such morphological characters suggested that these microorganisms are stramenopile protists and in particular thraustochytrids. Molecular analysis, carried out using specific primers for stramenopile 18S rRNA genes, revealed that 90% (111/123) of the clones in the gene libraries were from the Thraustochytriidae. The dominant genera in this family were Aplanochytrium sp., Thraustochytrium sp., and Labyrinthuloides sp. Ten stramenopile strains were isolated and cultured from the corals. Some strains showed > or =97% similarity to clones derived from libraries of mucus-associated microorganisms retrieved directly from these corals. Fatty acid characterization of one of the prevalent strains revealed a high percentage of polyunsaturated fatty acids, including omega-3. The possible association of these stramenopiles in the coral holobiont appeared to be a positive one.
Publisher: Oxford University Press (OUP)
Date: 15-04-2008
DOI: 10.1111/J.1574-6941.2008.00464.X
Abstract: Recent evidence suggests that there is a dynamic microbial biota living on the surface and in the mucus layer of many hermatypic coral species that plays an essential role in coral well-being. Most of the studies published to date emphasize the importance of prokaryotic communities associated with the coral mucus in coral health and disease. In this study, we report the presence of a protist (Fng1) in the mucus of the hermatypic coral Fungia granulosa from the Gulf of Eilat. This protist was identified morphologically and molecularly as belonging to the family Thraustochytridae (phylum Stramenopile, order Labyrinthulida), a group of heterotrophs widely distributed in the marine environment. Morphological examination of this strain revealed a nonmotile organism c. 35 mum in diameter, which is able to thrive on carbon-deprived media, and whose growth and morphology are inoculum dependent. Its fatty acid production profile revealed an array of polyunsaturated fatty acids. A similar protist was also isolated from the mucus of the coral Favia sp. In light of these findings, its possible contribution to the coral holobiont is discussed.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.JMB.2011.09.021
Abstract: During sporulation, Bacillus thuringiensis subsp. israelensis produces a mosquito larvicidal protein complex containing several crystalline and cytolytic (Cyt) toxins. Here, the activated monomeric form of Cyt1Aa, the most toxic Cyt family member, was isolated and crystallized, and its structure was determined for the first time at 2.2 Å resolution. Cyt1Aa adopts a typical cytolysin fold containing a β-sheet held by two surrounding α-helical layers. The absence of a β-strand (between residues V26 and I37) in the dimeric structure of Cyt2Aa led us to deduce that this is the only essential segment for dimer formation and that activation of the toxin occurs by proteolytic processing of its N-terminus. Based on the Cyt1Aa structure, we suggest that the toxicity of Cyt1Aa and other nonrelated proteins, all sharing a cytolysin fold, is correlated with their ability to undergo conformational changes that are necessary prior to their membrane insertion and perforation. This fold allows the α-helical layers to swing away, exposing the β-sheet to insert into the membrane. The identification of a putative lipid binding pocket between the β-sheet and the helical layer of Cyt1Aa supports this mechanism. Sequence-based structural analysis of Cyt1Aa revealed that the lack of activity of Cyt1Ca may be related to the latter's inability to undergo this conformational change due to its lack of flexibility. The pattern of the hemolytic activity of Cyt1Aa presented here (resembling that of pore-forming agents), while differing from that imposed by ionic and nonionic detergents, further supports the pore-forming model by which conformational changes occur prior to membrane insertion and perforation.
Publisher: Elsevier BV
Date: 07-2008
DOI: 10.1016/J.JMB.2008.05.010
Abstract: The Cyt family of proteins consists of delta-endotoxins expressed during sporulation of several subspecies of Bacillus thuringiensis. Its members possess insecticidal, hemolytic, and cytolytic activities through pore formation and attract attention due to their potential use as vehicles for targeted membrane destruction. The delta-endotoxins of subsp. israelensis include three Cyt species: a major Cyt1Aa and two minor proteins, Cyt2Ba and Cyt1Ca. A cleaved Cyt protein that lacks the N- and C-terminal segments forms a toxic monomer. Here, we describe the crystal structure of Cyt2Ba, cleaved at its amino and carboxy termini by bacterial endogenous protease(s). Overall, its fold resembles that of the previously described volvatoxin A2 and the nontoxic form of Cyt2Aa. The structural similarity between these three proteins may provide information regarding the mechanism(s) of membrane-perforating toxins.
Publisher: American Society for Microbiology
Date: 11-2006
DOI: 10.1128/AEM.00849-06
Abstract: To overcome the shortcomings of universal 16S rRNA gene primers 8F and 907R when studying the ersity of complex microbial communities, the 3′ termini of both primers were replaced with inosine. A comparison of the clone libraries derived using both primer sets showed seven bacterial phyla lified by the altered primer set (8F-I/907R-I) whereas the original set lified sequences belonging almost exclusively to Proteobacteria (95.8%). Sequences belonging to Firmicutes (42.6%) and Thermotogae (9.3%) were more abundant in a library obtained by using 8F-I/907R-I at a PCR annealing temperature of 54°C, while Proteobacteria sequences were more frequent (62.7%) in a library obtained at 50°C, somewhat resembling the result obtained using the original primer set. The increased ersity revealed by using primers 8F-I/907R-I confirms the usefulness of primers with inosine at the 3′ termini in studying the microbial ersity of environmental s les.
No related grants have been discovered for Eitan Ben-Dov.