Mohammad Al-Najjar - Academia.edu (original) (raw)
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Papers by Mohammad Al-Najjar
Here we present, to the best of our knowledge, the first balanced light energy budget for a benth... more Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (J abs ). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with 499% of the absorbed light energy being dissipated as heat and o1% used by photosynthesis at J abs 4700 lmol photon m À2 s À1 (4150 J m À2 s À1 ). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014À0.047 O 2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at J abs 4700 lmol photon m À2 s À1 , they reached around 10% of the maximum values at depths 0À0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.
Applied and Environmental Microbiology, 2009
Here we describe a spectral imaging system for minimally invasive identification, localization, a... more Here we describe a spectral imaging system for minimally invasive identification, localization, and relative quantification of pigments in cells and microbial communities. The modularity of the system allows pigment detection on spatial scales ranging from the single-cell level to regions whose areas are several tens of square centimeters. For pigment identification in vivo absorption and/or autofluorescence spectra are used as the analytical signals. Along with the hardware, which is easy to transport and simple to assemble and allows rapid measurement, we describe newly developed software that allows highly sensitive and pigment-specific analyses of the hyperspectral data. We also propose and describe a number of applications of the system for microbial ecology, including identification of pigments in living cells and high-spatial-resolution imaging of pigments and the associated phototrophic groups in complex microbial communities, such as photosynthetic endolithic biofilms, microbial mats, and intertidal sediments. This system provides new possibilities for studying the role of spatial organization of microorganisms in the ecological functioning of complex benthic microbial communities or for noninvasively monitoring changes in the spatial organization and/or composition of a microbial community in response to changing environmental factors.
We describe a spectral imaging system for minimally invasive identification, 19 localization and ... more We describe a spectral imaging system for minimally invasive identification, 19 localization and relative quantification of pigments in cells and microbial 20 communities. The modularity of the system allows pigment detection on spatial scales 21 ranging from single-cell level to areas several tens of square-cm. Pigment 22 identification uses in vivo absorption and/or auto-fluorescence spectra as the 23 analytical signal. Along with the hardware, which is easy to transport, simple to 24 assemble and allows rapid measurements, we describe newly developed software that 25 allows highly sensitive and pigment-specific analyses of the hyperspectral data. We 26 also propose and describe a number of applications of the system in the field of 27 microbial ecology, including identification of pigments in living cells and high spatial 28 resolution imaging of pigments and the associated phototrophic groups in complex 29 microbial communities such as photosynthetic endolithic biofilms, microbial mats, 30 and intertidal sediments. The system opens new possibilities to study the role of 31 spatial organization of microorganisms in the ecological functioning of complex 32 benthic microbial communities, or to non-invasively monitor changes in the spatial 33 organization and/or composition of a microbial community in response to changing 34 environmental factors. 35 36 Spectral imaging is a technique in which spectral information (i.e., the spectrum of 37 light that is scattered from, transmitted through or emitted by an object) is acquired at 38 every location of an image. Since the spectral information reflects the object's 39 identity, status and/or composition, combining it with the spatial information (i.e., 40 size, shape and location of objects) enhances our capability to unravel and understand 41
Spectrally resolved imaging was applied to study the growth dynamics of phototrophic biofilms com... more Spectrally resolved imaging was applied to study the growth dynamics of phototrophic biofilms comprizing a mixture of one cyanobacterial and one diatom species. Linear spectral unmixing was combined with liquid chromatography to quantitatively discriminate the areal biomass densities of the two populations. The grown biofilms exhibited highly heterogeneous distribution with patches of 1-2 mm in size, although the conditions provided for growth, including substrate roughness, illumination and flow of the overlying water, were homogeneous. The biomass was initially dominated by cyanobacteria, which exhibited an exponential-like growth phase during days 2-7. Their population declined during days 9-17, which coincided with the growth phase of the diatom population. By allowing non-invasive and real-time measurements and data evaluation, the spectral imaging approach constitutes a useful tool for microbial ecologists.
Isme Journal, 2010
Here we present, to the best of our knowledge, the first balanced light energy budget for a benth... more Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (J abs ). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with 499% of the absorbed light energy being dissipated as heat and o1% used by photosynthesis at J abs 4700 lmol photon m À2 s À1 (4150 J m À2 s À1 ). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014À0.047 O 2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at J abs 4700 lmol photon m À2 s À1 , they reached around 10% of the maximum values at depths 0À0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.
Here we present, to the best of our knowledge, the first balanced light energy budget for a benth... more Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (J abs ). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with 499% of the absorbed light energy being dissipated as heat and o1% used by photosynthesis at J abs 4700 lmol photon m À2 s À1 (4150 J m À2 s À1 ). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014À0.047 O 2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at J abs 4700 lmol photon m À2 s À1 , they reached around 10% of the maximum values at depths 0À0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.
Applied and Environmental Microbiology, 2009
Here we describe a spectral imaging system for minimally invasive identification, localization, a... more Here we describe a spectral imaging system for minimally invasive identification, localization, and relative quantification of pigments in cells and microbial communities. The modularity of the system allows pigment detection on spatial scales ranging from the single-cell level to regions whose areas are several tens of square centimeters. For pigment identification in vivo absorption and/or autofluorescence spectra are used as the analytical signals. Along with the hardware, which is easy to transport and simple to assemble and allows rapid measurement, we describe newly developed software that allows highly sensitive and pigment-specific analyses of the hyperspectral data. We also propose and describe a number of applications of the system for microbial ecology, including identification of pigments in living cells and high-spatial-resolution imaging of pigments and the associated phototrophic groups in complex microbial communities, such as photosynthetic endolithic biofilms, microbial mats, and intertidal sediments. This system provides new possibilities for studying the role of spatial organization of microorganisms in the ecological functioning of complex benthic microbial communities or for noninvasively monitoring changes in the spatial organization and/or composition of a microbial community in response to changing environmental factors.
We describe a spectral imaging system for minimally invasive identification, 19 localization and ... more We describe a spectral imaging system for minimally invasive identification, 19 localization and relative quantification of pigments in cells and microbial 20 communities. The modularity of the system allows pigment detection on spatial scales 21 ranging from single-cell level to areas several tens of square-cm. Pigment 22 identification uses in vivo absorption and/or auto-fluorescence spectra as the 23 analytical signal. Along with the hardware, which is easy to transport, simple to 24 assemble and allows rapid measurements, we describe newly developed software that 25 allows highly sensitive and pigment-specific analyses of the hyperspectral data. We 26 also propose and describe a number of applications of the system in the field of 27 microbial ecology, including identification of pigments in living cells and high spatial 28 resolution imaging of pigments and the associated phototrophic groups in complex 29 microbial communities such as photosynthetic endolithic biofilms, microbial mats, 30 and intertidal sediments. The system opens new possibilities to study the role of 31 spatial organization of microorganisms in the ecological functioning of complex 32 benthic microbial communities, or to non-invasively monitor changes in the spatial 33 organization and/or composition of a microbial community in response to changing 34 environmental factors. 35 36 Spectral imaging is a technique in which spectral information (i.e., the spectrum of 37 light that is scattered from, transmitted through or emitted by an object) is acquired at 38 every location of an image. Since the spectral information reflects the object's 39 identity, status and/or composition, combining it with the spatial information (i.e., 40 size, shape and location of objects) enhances our capability to unravel and understand 41
Spectrally resolved imaging was applied to study the growth dynamics of phototrophic biofilms com... more Spectrally resolved imaging was applied to study the growth dynamics of phototrophic biofilms comprizing a mixture of one cyanobacterial and one diatom species. Linear spectral unmixing was combined with liquid chromatography to quantitatively discriminate the areal biomass densities of the two populations. The grown biofilms exhibited highly heterogeneous distribution with patches of 1-2 mm in size, although the conditions provided for growth, including substrate roughness, illumination and flow of the overlying water, were homogeneous. The biomass was initially dominated by cyanobacteria, which exhibited an exponential-like growth phase during days 2-7. Their population declined during days 9-17, which coincided with the growth phase of the diatom population. By allowing non-invasive and real-time measurements and data evaluation, the spectral imaging approach constitutes a useful tool for microbial ecologists.
Isme Journal, 2010
Here we present, to the best of our knowledge, the first balanced light energy budget for a benth... more Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (J abs ). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with 499% of the absorbed light energy being dissipated as heat and o1% used by photosynthesis at J abs 4700 lmol photon m À2 s À1 (4150 J m À2 s À1 ). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014À0.047 O 2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at J abs 4700 lmol photon m À2 s À1 , they reached around 10% of the maximum values at depths 0À0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.