naglaa mohamed - Academia.edu (original) (raw)

Papers by naglaa mohamed

Research paper thumbnail of Equilibrium Studies of Ternary Systems Involving Divalent Transition Metal Ions, Aliphatic Acids, and Triazoles

Journal of Chemical and Engineering Data, 2002

ABSTRACT

Research paper thumbnail of Equilibrium Studies of Ternary Systems Involving Divalent Transition Metal Ions, Aliphatic Acids, and Triazoles

Journal of Chemical and Engineering Data, 2002

ABSTRACT

Research paper thumbnail of Diversity and expression of nitrogen fixation genes in bacterial symbionts of marine sponges

Environmental Microbiology, 2008

Marine sponges contain complex assemblages of bacterial symbionts, the roles of which remain larg... more Marine sponges contain complex assemblages of bacterial symbionts, the roles of which remain largely unknown. We identified diverse bacterial nifH genes within sponges and found that nifH genes are expressed in sponges. This is the first demonstration of the expression of any protein-coding bacterial gene within a sponge. Two sponges Ircinia strobilina and Mycale laxissima were collected from Key Largo, Florida and had δ15N values of c. 0–1‰ and 3–4‰ respectively. The potential for nitrogen fixation by symbionts was assessed by amplification of nifH genes. Diverse nifH genes affiliated with Proteobacteria and Cyanobacteria were detected, and expression of nifH genes affiliated with those from cyanobacteria was detected. The nifH genes from surrounding seawater were similar to those of Trichodesmium and clearly different from the cyanobacterial nifH genes detected in the two sponges. This study advances understanding of the role of bacterial symbionts in sponges and suggests that provision of fixed nitrogen is a means whereby symbionts benefit sponges in nutrient-limited reef environments. Nitrogen fixation by sponge symbionts is possibly an important source of new nitrogen to the reef environment that heretofore has been neglected and warrants further investigation.

Research paper thumbnail of Diversity and quorum-sensing signal production of Proteobacteria associated with marine sponges

Environmental Microbiology, 2007

Marine sponges are hosts to diverse and dense bacterial communities and thus provide a potential ... more Marine sponges are hosts to diverse and dense bacterial communities and thus provide a potential environment for quorum sensing. Quorum sensing, a key factor in cell–cell communication and bacterial colonization of higher animals, might be involved in the symbiotic interactions between bacteria and their sponge hosts. Given that marine Proteobacteria are known to produce N-acyl homoserine lactone (AHL) signal molecules, we tested the production of AHLs by Alpha- and Gammaproteobacteria isolated from marine sponges Mycale laxissima and Ircinia strobilina and the surrounding water column. We used three different AHL biodetection systems in diffusion assays: Chromobacterium violaceum, Agrobacterium tumefaciens and Sinorhizobium meliloti with optimal sensitivity to short-chain (C4–C6), moderate-chain (C8–C12) and long-chain (≥ C14) AHLs respectively. Thirteen of 23 isolates from M. laxissima and five of 25 isolates from I. strobilina were found to produce AHLs. Signals were detected from two of eight proteobacterial strains from the water column. Thin-layer chromatographic assays based on the A. tumefaciens reporter system were utilized to determine the AHL profiles of the positive isolates. The types and amounts of AHLs synthesized varied considerably among the strains. Small ribosomal rRNA gene sequencing revealed that the AHL-producing alphaproteobacterial isolates were mainly from the Silicibacter–Ruegeria subgroup of the Roseobacter clade. Two-dimensional gel electrophoresis (2DGE)-based proteomic analyses were congruent with phylogenetic relationships but provided higher resolution to differentiate these closely related AHL-producing strains.

Research paper thumbnail of Changes in Bacterial Communities of the Marine Sponge Mycale laxissima on Transfer into Aquaculture

Applied and Environmental Microbiology, 2008

Research paper thumbnail of Monitoring Bacterial Diversity of the Marine Sponge Ircinia strobilina upon Transfer into Aquaculture

Applied and Environmental Microbiology, 2008

Research paper thumbnail of Novel actinobacteria from marine sponges

Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology, 2005

Actinobacteria exclusively within the sub-class Acidimicrobidae were shown by 16S rDNA community ... more Actinobacteria exclusively within the sub-class Acidimicrobidae were shown by 16S rDNA community analysis to be major components of the bacterial community associated with two sponge species in the genus Xestospongia. Four groups of Actinobacteria were identified in Xestospongia spp., with three of these four groups being found in both Xestospongia muta from Key Largo, Florida and Xestospongia testudinaria from Manado, Indonesia. This suggests that these groups are true symbionts in these sponges and may play a common role in both the Pacific and Atlantic sponge species. The fourth group was found only in X. testudinaria and was a novel assemblage distantly related to any previously sequenced actinobacterial clones. The only actinobacteria that were obtained in initial culturing attempts were Gordonia, Micrococcus and Brachybacterium spp., none of which were represented in the clone libraries. The closest cultured actinobacteria to all the Acidimicrobidae clones from Xestospongia spp. are ‘Microthrix parvicella’ and Acidimicrobium spp. Xestospongia spp. can now be targeted as source material from which to culture novel Acidimicrobidae to investigate their potential as producers of bioactive compounds. Isolation of sponge-associated Acidimicrobidae will also make it possible to elucidate their role as sponge symbionts.

Research paper thumbnail of Bacterial Community Analyses of Two Red Sea Sponges

Marine Biotechnology, 2010

Red Sea sponges offer potential as sources of novel drugs and bioactive compounds. Sponges harbor... more Red Sea sponges offer potential as sources of novel drugs and bioactive compounds. Sponges harbor diverse and abundant prokaryotic communities. The diversity of Egyptian sponge-associated bacterial communities has not yet been explored. Our study is the first culture-based and culture-independent investigation of the total bacterial assemblages associated with two Red Sea Demosponges, Hyrtios erectus and Amphimedon sp. Denaturing gradient gel electrophoresis fingerprint-based analysis revealed statistically different banding patterns of the bacterial communities of the studied sponges with H. erectus having the greater diversity. 16S rRNA clone libraries of both sponges revealed diverse and complex bacterial assemblages represented by ten phyla for H. erectus and five phyla for Amphimedon sp. The bacterial community associated with H. erectus was dominated by Deltaproteobacteria. Clones affiliated with Gammaproteobacteria were the major component of the clone library of Amphimedon sp. About a third of the 16S rRNA gene sequences in these communities were derived from bacteria that are novel at least at the species level. Although the overall bacterial communities were significantly different, some bacterial groups, including members of Alphaproteobacteria, Gammaproteobacteria, Acidobacteria, and Actinobacteria, were found in both sponge species. The culture-based component of this study targeted Actinobacteria and resulted in the isolation of 35 sponge-associated microbes. The current study lays the groundwork for future studies of the role of these diverse microbes in the ecology, evolution, and development of marine sponges. In addition, our work provides an excellent resource of several candidate bacteria for production of novel pharmaceutically important compounds.

Research paper thumbnail of Diversity of aerobic and anaerobic ammonia-oxidizing bacteria in marine sponges

Research paper thumbnail of Equilibrium Studies of Ternary Systems Involving Divalent Transition Metal Ions, Aliphatic Acids, and Triazoles

Journal of Chemical and Engineering Data, 2002

ABSTRACT

Research paper thumbnail of Equilibrium Studies of Ternary Systems Involving Divalent Transition Metal Ions, Aliphatic Acids, and Triazoles

Journal of Chemical and Engineering Data, 2002

ABSTRACT

Research paper thumbnail of Diversity and expression of nitrogen fixation genes in bacterial symbionts of marine sponges

Environmental Microbiology, 2008

Marine sponges contain complex assemblages of bacterial symbionts, the roles of which remain larg... more Marine sponges contain complex assemblages of bacterial symbionts, the roles of which remain largely unknown. We identified diverse bacterial nifH genes within sponges and found that nifH genes are expressed in sponges. This is the first demonstration of the expression of any protein-coding bacterial gene within a sponge. Two sponges Ircinia strobilina and Mycale laxissima were collected from Key Largo, Florida and had δ15N values of c. 0–1‰ and 3–4‰ respectively. The potential for nitrogen fixation by symbionts was assessed by amplification of nifH genes. Diverse nifH genes affiliated with Proteobacteria and Cyanobacteria were detected, and expression of nifH genes affiliated with those from cyanobacteria was detected. The nifH genes from surrounding seawater were similar to those of Trichodesmium and clearly different from the cyanobacterial nifH genes detected in the two sponges. This study advances understanding of the role of bacterial symbionts in sponges and suggests that provision of fixed nitrogen is a means whereby symbionts benefit sponges in nutrient-limited reef environments. Nitrogen fixation by sponge symbionts is possibly an important source of new nitrogen to the reef environment that heretofore has been neglected and warrants further investigation.

Research paper thumbnail of Diversity and quorum-sensing signal production of Proteobacteria associated with marine sponges

Environmental Microbiology, 2007

Marine sponges are hosts to diverse and dense bacterial communities and thus provide a potential ... more Marine sponges are hosts to diverse and dense bacterial communities and thus provide a potential environment for quorum sensing. Quorum sensing, a key factor in cell–cell communication and bacterial colonization of higher animals, might be involved in the symbiotic interactions between bacteria and their sponge hosts. Given that marine Proteobacteria are known to produce N-acyl homoserine lactone (AHL) signal molecules, we tested the production of AHLs by Alpha- and Gammaproteobacteria isolated from marine sponges Mycale laxissima and Ircinia strobilina and the surrounding water column. We used three different AHL biodetection systems in diffusion assays: Chromobacterium violaceum, Agrobacterium tumefaciens and Sinorhizobium meliloti with optimal sensitivity to short-chain (C4–C6), moderate-chain (C8–C12) and long-chain (≥ C14) AHLs respectively. Thirteen of 23 isolates from M. laxissima and five of 25 isolates from I. strobilina were found to produce AHLs. Signals were detected from two of eight proteobacterial strains from the water column. Thin-layer chromatographic assays based on the A. tumefaciens reporter system were utilized to determine the AHL profiles of the positive isolates. The types and amounts of AHLs synthesized varied considerably among the strains. Small ribosomal rRNA gene sequencing revealed that the AHL-producing alphaproteobacterial isolates were mainly from the Silicibacter–Ruegeria subgroup of the Roseobacter clade. Two-dimensional gel electrophoresis (2DGE)-based proteomic analyses were congruent with phylogenetic relationships but provided higher resolution to differentiate these closely related AHL-producing strains.

Research paper thumbnail of Changes in Bacterial Communities of the Marine Sponge Mycale laxissima on Transfer into Aquaculture

Applied and Environmental Microbiology, 2008

Research paper thumbnail of Monitoring Bacterial Diversity of the Marine Sponge Ircinia strobilina upon Transfer into Aquaculture

Applied and Environmental Microbiology, 2008

Research paper thumbnail of Novel actinobacteria from marine sponges

Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology, 2005

Actinobacteria exclusively within the sub-class Acidimicrobidae were shown by 16S rDNA community ... more Actinobacteria exclusively within the sub-class Acidimicrobidae were shown by 16S rDNA community analysis to be major components of the bacterial community associated with two sponge species in the genus Xestospongia. Four groups of Actinobacteria were identified in Xestospongia spp., with three of these four groups being found in both Xestospongia muta from Key Largo, Florida and Xestospongia testudinaria from Manado, Indonesia. This suggests that these groups are true symbionts in these sponges and may play a common role in both the Pacific and Atlantic sponge species. The fourth group was found only in X. testudinaria and was a novel assemblage distantly related to any previously sequenced actinobacterial clones. The only actinobacteria that were obtained in initial culturing attempts were Gordonia, Micrococcus and Brachybacterium spp., none of which were represented in the clone libraries. The closest cultured actinobacteria to all the Acidimicrobidae clones from Xestospongia spp. are ‘Microthrix parvicella’ and Acidimicrobium spp. Xestospongia spp. can now be targeted as source material from which to culture novel Acidimicrobidae to investigate their potential as producers of bioactive compounds. Isolation of sponge-associated Acidimicrobidae will also make it possible to elucidate their role as sponge symbionts.

Research paper thumbnail of Bacterial Community Analyses of Two Red Sea Sponges

Marine Biotechnology, 2010

Red Sea sponges offer potential as sources of novel drugs and bioactive compounds. Sponges harbor... more Red Sea sponges offer potential as sources of novel drugs and bioactive compounds. Sponges harbor diverse and abundant prokaryotic communities. The diversity of Egyptian sponge-associated bacterial communities has not yet been explored. Our study is the first culture-based and culture-independent investigation of the total bacterial assemblages associated with two Red Sea Demosponges, Hyrtios erectus and Amphimedon sp. Denaturing gradient gel electrophoresis fingerprint-based analysis revealed statistically different banding patterns of the bacterial communities of the studied sponges with H. erectus having the greater diversity. 16S rRNA clone libraries of both sponges revealed diverse and complex bacterial assemblages represented by ten phyla for H. erectus and five phyla for Amphimedon sp. The bacterial community associated with H. erectus was dominated by Deltaproteobacteria. Clones affiliated with Gammaproteobacteria were the major component of the clone library of Amphimedon sp. About a third of the 16S rRNA gene sequences in these communities were derived from bacteria that are novel at least at the species level. Although the overall bacterial communities were significantly different, some bacterial groups, including members of Alphaproteobacteria, Gammaproteobacteria, Acidobacteria, and Actinobacteria, were found in both sponge species. The culture-based component of this study targeted Actinobacteria and resulted in the isolation of 35 sponge-associated microbes. The current study lays the groundwork for future studies of the role of these diverse microbes in the ecology, evolution, and development of marine sponges. In addition, our work provides an excellent resource of several candidate bacteria for production of novel pharmaceutically important compounds.

Research paper thumbnail of Diversity of aerobic and anaerobic ammonia-oxidizing bacteria in marine sponges