Nicholas Owens | University of the Highlands and Islands - UHI (original) (raw)
Papers by Nicholas Owens
Cyclic Phenomena in Marine Plants and Animals, 1979
Sediments from the Eden estuary on the east coast of Scotland were examined for the presence of n... more Sediments from the Eden estuary on the east coast of Scotland were examined for the presence of nitrifying bacteria using a MPN technique, selective media, and N-Serve, an inhibitor of autotrophic nitrification. Both autotrophic and heterotrophic nitrifiers were found. Autotrophic forms were always more abundant and more active than heterotrophic forms. Evidence was obtained that certain of the autotrophic nitrifiers may have been of terrestrial or freshwater origin and that certain of the heterotrophic isolates were truly marine.
Estuarine, Coastal and Shelf Science, 1983
The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined ov... more The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined over a twelve-month period. Nitrogen assimilation rates using 15N have been used to calculate the production of the alga and were between 0.046 and 0.217 mg NH,+-N (g dry wt alga)-] h-1 A considerable quantity of the alga was buried beneath the sediment over the, growth season and was calculated to be equivalent to an input of up to 9.52 g N m-2 per month and 32 g N m-2 over one complete growth season. Based on carbon, this latter value represented an input of approximately 320 g C m-2 annually. Low rates of nitrogenase activity (acetylene reduction) were found to be associated with the Enteromorpha. The organisms responsible for the nitrogenase activity were probably heterotrophic bacteria but they did not contribute significant quantities of nitrogen to the alga.
Science, 2007
Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has r... more Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has radically changed. Mesoscale iron addition experiments (FeAXs) have unequivocally shown that iron supply limits production in one-third of the world ocean, where surface macronutrient concentrations are perennially high. The findings of these 12 FeAXs also reveal that iron supply exerts controls on the dynamics of plankton blooms, which in turn affect the biogeochemical cycles of carbon, nitrogen, silicon, and sulfur and ultimately influence the Earth climate system. However, extrapolation of the key results of FeAXs to regional and seasonal scales in some cases is limited because of differing modes of iron supply in FeAXs and in the modern and paleo-oceans. New research directions include quantification of the coupling of oceanic iron and carbon biogeochemistry.
Marine Ecology Progress Series, 1999
Oceanic new production is a potential avenue for the removal of atmospheric carbon dioxide to the... more Oceanic new production is a potential avenue for the removal of atmospheric carbon dioxide to the deep abyss. The ability to estimate new production on large, ocean-basin scales has important implications for studies of the greenhouse effect. This paper describes the development of a method whlch will allow real-time estimates of new production on ocean-basin scales, given real-time data on ocean colour and sea-surface temperature from satellites. This study has concentrated on the northwest Indian Ocean region but the protocol developed could be geographically transportable. Results from a biogeochernical study carried out in the northwest Indian Ocean during a monsoon and an intermonsoon period in 1994 indicate that this region can be partitioned into 6 distinct provinces based on bathymetry, sea-surface temperature and chlorophyll measurements. Parameters that define the vertical structure in the biomass profile and the photosynthesis-light curve have been established for each province and these, in combination with archived satellite data, are used to compute the primary production for each province using an established light-dependent model. From our empirically derived relationship between the f-ratio and primary production, new production for the northwest Indian Ocean over these 2 different seasons is computed. KEY WORDS: New production. f-ratio-Primary production. Biogeochernical provinces-Satellite remote sensing. Modehng. Northwest Indian Ocean
Deep Sea Research Part II: Topical Studies in Oceanography, 1995
... Nelson and Smith, 1986), but by far the greatest concentration of work has been in the Weddel... more ... Nelson and Smith, 1986), but by far the greatest concentration of work has been in the Weddell and Scotia Seas (Cota et al., 1992; Olson, 1980; Glibert et al.,1982; Koike et al.,1981,1986; Ronner et al.,1983; Owens et al.,1991; Smith and Nelson, 1987, 1990; Kristiansen et al ...
Marine Ecology Progress Series, 1995
Three sites along a shelf to deep-sea transect near the island of South Georgia (55' S) were samp... more Three sites along a shelf to deep-sea transect near the island of South Georgia (55' S) were sampled in the latter part of the austral summer for water column structure, inorganic nutrients, particulate material and microplankton. Median concentrations at the 3 sites were 17 to 24 mrnol m-3 nitrate and approximately 1.6 mmol m-3 phosphate, whilst silicate concentrations remained at 11 mmol m-3 nearshore but were reduced to approximately 1 mmol m 3 offshore. Microplankton community composition appeared to be characteristic of post-bloom conditions. Heterotrophs, including large protists, dominated microbial biomass at the offshore site. Pigment characterisation was consistent with the domination of the microplankton by diatoms at all sites. Changes in the carbon and nitrogen content of particulate material down the water column were consistent with significant remineralisation of nitrogen in the mixed layer, with molar C:N ratios of 6.5 to ?.? in surface waters and up to 11.9 immediately below the mixed layer. In most cases, peak concentrations of ammonium were found to be associated with the pycnocline, suggesting that remineralisation of nitrogen was occurring here. However, no component of the microbial community could be associated with this region of ammonium production. Carbon fixation over the growing season predicted from published instantaneous nitrogen uptake rates, from biological nitrate deficit in the mixed layer and from the corresponding silicate deficit suggested that at least 25 g C m 2 was produced by phytoplankton during the growth season. However, there is strong evidence that this is a serious underestimate Even whilst nitrate concentrations remained high, ammonium and possibly other 'recycled nitrogen' appeared to be key inorganic nutrients. Particulate carbon and silicon appeared to be removed from the mixed layer whilst nitrogen was regenerated in situ. In such systems, nitrate removal does not indicate carbon export, and nitrogen recycling may be a crucial factor in determining productivity throughout the growing season. KEY WORDS: Nutrient cycling. Antarctica. Carbon export. Marine microplankton. Nitrogen Silicon. Particulate material Community composition Present addresses: 1991)-diatoms dominate the spring bloom and are *Oslo and Paris Commissions, New Court, 48 Carey Street, consumed by large herbivores, whilst the regenerative London WC2A 2JE, United Kingdom "Department of Marine Science and Coastal Management, phase of the community comprises smaller primary The Ridley Building, The University of Newcastle upon producers grazed microheterotro~hs the micro-Tyne, Newcastle upon Tyne NE1 ?RU, United Kingdom bial loop. However, the use of the nitrate amount in the 1 Inter-Research 1995 Resale of full article not permitted
Applied and Environmental Microbiology, 1995
Two methylotrophic bacterial strains, TR3 and PSCH4, capable of growth on methanesulfonic acid as... more Two methylotrophic bacterial strains, TR3 and PSCH4, capable of growth on methanesulfonic acid as the sole carbon source were isolated from the marine environment. Methanesulfonic acid metabolism in these strains was initiated by an inducible NADH-dependent monooxygenase, which cleaved methanesulfonic acid into formaldehyde and sulfite. The presence of hydroxypyruvate reductase and the absence of ribulose monophosphate-dependent hexulose monophosphate synthase indicated the presence of the serine pathway for formaldehyde assimilation. Cell suspensions of bacteria grown on methanesulfonic acid completely oxidized methanesulfonic acid to carbon dioxide and sulfite with a methanesulfonic acid/oxygen stoichiometry of 1.0:2.0. Oxygen electrode-substrate studies indicated the dissimilation of formaldehyde to formate and carbon dioxide for energy generation. Carbon dioxide was not fixed by ribulose bisphosphate carboxylase. It was shown that methanol is not an intermediate in methanesulfon...
Transfer Processes in Cohesive Sediment Systems, 1984
It is well documented that aquatic sediments are sites of intensive microbial activity and that t... more It is well documented that aquatic sediments are sites of intensive microbial activity and that the majority of the processes which occur there involve the breakdown of organic matter and the subsequent transformations of the products of decomposition. Estuarine sediments typically have higher interstitial water concentrations of dissolved inorganic nitrogen (DIN) than in the overlying water column, suggesting that sediments are sites of active nitrogen cycling.
Journal of Integrative Environmental Sciences, 2016
Main text: 8,529, of which 2,635 in tables (including references, titles and subtitles) Text boxe... more Main text: 8,529, of which 2,635 in tables (including references, titles and subtitles) Text boxes: n/a Number of references: 105 Number of figures: Two (2) Number of tables: Three (3)
Cyclic Phenomena in Marine Plants and Animals, 1979
The concentrations of NO 3 -N and NH 4 -N in the interstitial waters of the Eden estuary mature s... more The concentrations of NO 3 -N and NH 4 -N in the interstitial waters of the Eden estuary mature salt marsh, developing marsh, and mud flat region are higher than those in the overlying water at high tide. The developing marsh and mud flat region become dominated by a profuse growth of Enteromorpha (mainly E. prolifera ) which begins in May, increases to a maximum in August and declines in September–October. At the time of maximum biomass standing crop values of 3.48 g N m -2 and 22.17 g C m -2 are obtained. At the end of the growth season, Enteromorpha becomes buried in the sand, heterotrophic bacterial populations including ammonifying bacteria build up and anaerobic conditions develop in the upper layers of the sediment. Thereafter increased populations of NH 4 + -oxidising bacteria develop in November–December as increased oxygenation of the upper sediment layers occurs as a result of turbulence in autumn and winter. Numbers of denitrifying bacteria are highest in winter. Biological N 2 -fixation also occurs in the estuarine sediments, with annual inputs of combined nitrogen ranging from 0.03 to 2.8 g N m -2 ann -1 . The overall data suggest that input of nitrogen by decaying algae such as Enteromorpha and by biological N 2 -fixation are important in contributing new nitrogen to the ecosystem and that there is a close interdependence between nitrogen input, carbon input and nitrogen cycling within such estuarine sediments.
Journal of Marine Systems, 1998
Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Oce... more Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature
Deep Sea Research Part II: Topical Studies in Oceanography, 1993
The nucleophilic substitution reactions of diethyl thiophosphinic chloride with substituted anili... more The nucleophilic substitution reactions of diethyl thiophosphinic chloride with substituted anilines (XC 6 H 4 NH 2) and deuterated anilines (XC 6 H 4 ND 2) are investigated kinetically in acetonitrile at 55.0 o C. The values of deuterium kinetic isotope effects (DKIEs; k H /k D) invariably increase from secondary inverse (k H /k D < 1) to primary normal (k H /k D > 1) as the nucleophiles change from the strongly basic to weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the gradual transition state (TS) variation from a predominant backside attack, via invariably increasing the fraction of a frontside attack, to a predominant frontside attack, in which the reaction mechanism is a concerted S N 2 pathway. A frontside attack involving a hydrogen bonded, four-center-type TS is substantiated by the primary normal DKIEs.
PLOS ONE, 2015
The Vibrio cholerae N-acetyl glucosamine-binding protein A (GbpA) is a chitin-binding protein inv... more The Vibrio cholerae N-acetyl glucosamine-binding protein A (GbpA) is a chitin-binding protein involved in V. cholerae attachment to environmental chitin surfaces and human intestinal cells. We previously investigated the distribution and genetic variations of gbpA in a large collection of V. cholerae strains and found that the gene is consistently present and highly conserved in this species. Primers and probe were designed from the gbpA sequence of V. cholerae and a new Taq-based qPCR protocol was developed for diagnostic detection and quantification of the bacterium in environmental and stool samples. In addition, the positions of primers targeting the gbpA gene region were selected to obtain a short amplified fragment of 206 bp and the protocol was optimized for the analysis of formalinfixed samples, such as historical Continuous Plankton Recorder (CPR) samples. Overall, the method is sensitive (50 gene copies), highly specific for V. cholerae and failed to amplify strains of the closely-related species Vibrio mimicus. The sensitivity of the assay applied to environmental and stool samples spiked with V. cholerae ATCC 39315 was comparable to that of pure cultures and was of 10 2 genomic units/l for drinking and seawater samples, 10 1 genomic units/g for sediment and 10 2 genomic units/g for bivalve and stool samples. The method also performs well when tested on artificially formalin-fixed and degraded genomic samples and was able to amplify V. cholerae DNA in historical CPR samples, the earliest of which date back to August 1966. The detection of V. cholerae in CPR samples collected in cholera endemic areas such as the Benguela Current Large Marine Ecosystem (BCLME) is of particular significance and represents a proof of concept for the possible use of the CPR technology and the developed qPCR assay in cholera studies.
Deep Sea Research Part II: Topical Studies in Oceanography, 1993
The abundance, distribution, size, biomass, growth and grazing-induced mortality of phycoerythrin... more The abundance, distribution, size, biomass, growth and grazing-induced mortality of phycoerythrin (PE) rich chrococcoid cyanobacteria were studied during September-October 1986 in the Arabian Sea, the Gulf of Oman and the monsoonal upwelling region off the South East Arabian ...
Nature, 1991
ATMOSPHERIC concentrations of methane, an important greenhouse gas, have increased significantly ... more ATMOSPHERIC concentrations of methane, an important greenhouse gas, have increased significantly over the past few decades 1, 2. Although attention has been focused on anthropogenic sources, data from ice cores show that large changes in atmospheric ...
Advances in Marine Biology
... Similarly, it is impera-tive that C02 is removed from the combustion products since C02 will ... more ... Similarly, it is impera-tive that C02 is removed from the combustion products since C02 will &quot; crack&quot; to CO+ in the mass-spectrometer and will be detected at m/z 29. ... Natural variations in the absolute abundance of 14N and 15N occur at the 10~ 3 atom % level. ...
J Mass Spectrometry, 1985
Stable isotope tracer methods are gaining popularity in many fields, including environmental scie... more Stable isotope tracer methods are gaining popularity in many fields, including environmental science, agriculture and medicine. This is particularly true in the clinical sciences, where the use of radioisotopes can be precluded on ethical grounds and I3C and "N tracers are being used more frequently for metabolic studies. Mass spectrometry is the preferred technique for isotope analysis. Sample preparation techniques for classical isotope ratio mass spectrometry are often tedious and can involve the use of complex vacuum apparatus that is quite foreign to the biological chemist. Organic gas chromatography/mass spectrometry (GUMS) overcomes many sample preparation problems but may lack the performance needed for isotope analysis. This paper describes the analysis of I3C using an automatic elemental gas chromatograph interfaced to an isotope ratio mass spectrometer, a system which was developed initially for the analysis of "N. Details of the residual gas background, peak broadening due to high carrier gas pressures, mass spectral linearity and response to changing sample peak heights and variations of the measured isotope ratio with sample pressure are described. Sensitivity and performance data (reproducibility f 0.62% at natural abundance) are also given. The potential of this system for other gas chromatographic applications, automatic data handling and the possible simultaneous analysis of "C and "N are also discussed.
Cyclic Phenomena in Marine Plants and Animals, 1979
Sediments from the Eden estuary on the east coast of Scotland were examined for the presence of n... more Sediments from the Eden estuary on the east coast of Scotland were examined for the presence of nitrifying bacteria using a MPN technique, selective media, and N-Serve, an inhibitor of autotrophic nitrification. Both autotrophic and heterotrophic nitrifiers were found. Autotrophic forms were always more abundant and more active than heterotrophic forms. Evidence was obtained that certain of the autotrophic nitrifiers may have been of terrestrial or freshwater origin and that certain of the heterotrophic isolates were truly marine.
Estuarine, Coastal and Shelf Science, 1983
The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined ov... more The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined over a twelve-month period. Nitrogen assimilation rates using 15N have been used to calculate the production of the alga and were between 0.046 and 0.217 mg NH,+-N (g dry wt alga)-] h-1 A considerable quantity of the alga was buried beneath the sediment over the, growth season and was calculated to be equivalent to an input of up to 9.52 g N m-2 per month and 32 g N m-2 over one complete growth season. Based on carbon, this latter value represented an input of approximately 320 g C m-2 annually. Low rates of nitrogenase activity (acetylene reduction) were found to be associated with the Enteromorpha. The organisms responsible for the nitrogenase activity were probably heterotrophic bacteria but they did not contribute significant quantities of nitrogen to the alga.
Science, 2007
Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has r... more Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has radically changed. Mesoscale iron addition experiments (FeAXs) have unequivocally shown that iron supply limits production in one-third of the world ocean, where surface macronutrient concentrations are perennially high. The findings of these 12 FeAXs also reveal that iron supply exerts controls on the dynamics of plankton blooms, which in turn affect the biogeochemical cycles of carbon, nitrogen, silicon, and sulfur and ultimately influence the Earth climate system. However, extrapolation of the key results of FeAXs to regional and seasonal scales in some cases is limited because of differing modes of iron supply in FeAXs and in the modern and paleo-oceans. New research directions include quantification of the coupling of oceanic iron and carbon biogeochemistry.
Marine Ecology Progress Series, 1999
Oceanic new production is a potential avenue for the removal of atmospheric carbon dioxide to the... more Oceanic new production is a potential avenue for the removal of atmospheric carbon dioxide to the deep abyss. The ability to estimate new production on large, ocean-basin scales has important implications for studies of the greenhouse effect. This paper describes the development of a method whlch will allow real-time estimates of new production on ocean-basin scales, given real-time data on ocean colour and sea-surface temperature from satellites. This study has concentrated on the northwest Indian Ocean region but the protocol developed could be geographically transportable. Results from a biogeochernical study carried out in the northwest Indian Ocean during a monsoon and an intermonsoon period in 1994 indicate that this region can be partitioned into 6 distinct provinces based on bathymetry, sea-surface temperature and chlorophyll measurements. Parameters that define the vertical structure in the biomass profile and the photosynthesis-light curve have been established for each province and these, in combination with archived satellite data, are used to compute the primary production for each province using an established light-dependent model. From our empirically derived relationship between the f-ratio and primary production, new production for the northwest Indian Ocean over these 2 different seasons is computed. KEY WORDS: New production. f-ratio-Primary production. Biogeochernical provinces-Satellite remote sensing. Modehng. Northwest Indian Ocean
Deep Sea Research Part II: Topical Studies in Oceanography, 1995
... Nelson and Smith, 1986), but by far the greatest concentration of work has been in the Weddel... more ... Nelson and Smith, 1986), but by far the greatest concentration of work has been in the Weddell and Scotia Seas (Cota et al., 1992; Olson, 1980; Glibert et al.,1982; Koike et al.,1981,1986; Ronner et al.,1983; Owens et al.,1991; Smith and Nelson, 1987, 1990; Kristiansen et al ...
Marine Ecology Progress Series, 1995
Three sites along a shelf to deep-sea transect near the island of South Georgia (55' S) were samp... more Three sites along a shelf to deep-sea transect near the island of South Georgia (55' S) were sampled in the latter part of the austral summer for water column structure, inorganic nutrients, particulate material and microplankton. Median concentrations at the 3 sites were 17 to 24 mrnol m-3 nitrate and approximately 1.6 mmol m-3 phosphate, whilst silicate concentrations remained at 11 mmol m-3 nearshore but were reduced to approximately 1 mmol m 3 offshore. Microplankton community composition appeared to be characteristic of post-bloom conditions. Heterotrophs, including large protists, dominated microbial biomass at the offshore site. Pigment characterisation was consistent with the domination of the microplankton by diatoms at all sites. Changes in the carbon and nitrogen content of particulate material down the water column were consistent with significant remineralisation of nitrogen in the mixed layer, with molar C:N ratios of 6.5 to ?.? in surface waters and up to 11.9 immediately below the mixed layer. In most cases, peak concentrations of ammonium were found to be associated with the pycnocline, suggesting that remineralisation of nitrogen was occurring here. However, no component of the microbial community could be associated with this region of ammonium production. Carbon fixation over the growing season predicted from published instantaneous nitrogen uptake rates, from biological nitrate deficit in the mixed layer and from the corresponding silicate deficit suggested that at least 25 g C m 2 was produced by phytoplankton during the growth season. However, there is strong evidence that this is a serious underestimate Even whilst nitrate concentrations remained high, ammonium and possibly other 'recycled nitrogen' appeared to be key inorganic nutrients. Particulate carbon and silicon appeared to be removed from the mixed layer whilst nitrogen was regenerated in situ. In such systems, nitrate removal does not indicate carbon export, and nitrogen recycling may be a crucial factor in determining productivity throughout the growing season. KEY WORDS: Nutrient cycling. Antarctica. Carbon export. Marine microplankton. Nitrogen Silicon. Particulate material Community composition Present addresses: 1991)-diatoms dominate the spring bloom and are *Oslo and Paris Commissions, New Court, 48 Carey Street, consumed by large herbivores, whilst the regenerative London WC2A 2JE, United Kingdom "Department of Marine Science and Coastal Management, phase of the community comprises smaller primary The Ridley Building, The University of Newcastle upon producers grazed microheterotro~hs the micro-Tyne, Newcastle upon Tyne NE1 ?RU, United Kingdom bial loop. However, the use of the nitrate amount in the 1 Inter-Research 1995 Resale of full article not permitted
Applied and Environmental Microbiology, 1995
Two methylotrophic bacterial strains, TR3 and PSCH4, capable of growth on methanesulfonic acid as... more Two methylotrophic bacterial strains, TR3 and PSCH4, capable of growth on methanesulfonic acid as the sole carbon source were isolated from the marine environment. Methanesulfonic acid metabolism in these strains was initiated by an inducible NADH-dependent monooxygenase, which cleaved methanesulfonic acid into formaldehyde and sulfite. The presence of hydroxypyruvate reductase and the absence of ribulose monophosphate-dependent hexulose monophosphate synthase indicated the presence of the serine pathway for formaldehyde assimilation. Cell suspensions of bacteria grown on methanesulfonic acid completely oxidized methanesulfonic acid to carbon dioxide and sulfite with a methanesulfonic acid/oxygen stoichiometry of 1.0:2.0. Oxygen electrode-substrate studies indicated the dissimilation of formaldehyde to formate and carbon dioxide for energy generation. Carbon dioxide was not fixed by ribulose bisphosphate carboxylase. It was shown that methanol is not an intermediate in methanesulfon...
Transfer Processes in Cohesive Sediment Systems, 1984
It is well documented that aquatic sediments are sites of intensive microbial activity and that t... more It is well documented that aquatic sediments are sites of intensive microbial activity and that the majority of the processes which occur there involve the breakdown of organic matter and the subsequent transformations of the products of decomposition. Estuarine sediments typically have higher interstitial water concentrations of dissolved inorganic nitrogen (DIN) than in the overlying water column, suggesting that sediments are sites of active nitrogen cycling.
Journal of Integrative Environmental Sciences, 2016
Main text: 8,529, of which 2,635 in tables (including references, titles and subtitles) Text boxe... more Main text: 8,529, of which 2,635 in tables (including references, titles and subtitles) Text boxes: n/a Number of references: 105 Number of figures: Two (2) Number of tables: Three (3)
Cyclic Phenomena in Marine Plants and Animals, 1979
The concentrations of NO 3 -N and NH 4 -N in the interstitial waters of the Eden estuary mature s... more The concentrations of NO 3 -N and NH 4 -N in the interstitial waters of the Eden estuary mature salt marsh, developing marsh, and mud flat region are higher than those in the overlying water at high tide. The developing marsh and mud flat region become dominated by a profuse growth of Enteromorpha (mainly E. prolifera ) which begins in May, increases to a maximum in August and declines in September–October. At the time of maximum biomass standing crop values of 3.48 g N m -2 and 22.17 g C m -2 are obtained. At the end of the growth season, Enteromorpha becomes buried in the sand, heterotrophic bacterial populations including ammonifying bacteria build up and anaerobic conditions develop in the upper layers of the sediment. Thereafter increased populations of NH 4 + -oxidising bacteria develop in November–December as increased oxygenation of the upper sediment layers occurs as a result of turbulence in autumn and winter. Numbers of denitrifying bacteria are highest in winter. Biological N 2 -fixation also occurs in the estuarine sediments, with annual inputs of combined nitrogen ranging from 0.03 to 2.8 g N m -2 ann -1 . The overall data suggest that input of nitrogen by decaying algae such as Enteromorpha and by biological N 2 -fixation are important in contributing new nitrogen to the ecosystem and that there is a close interdependence between nitrogen input, carbon input and nitrogen cycling within such estuarine sediments.
Journal of Marine Systems, 1998
Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Oce... more Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature
Deep Sea Research Part II: Topical Studies in Oceanography, 1993
The nucleophilic substitution reactions of diethyl thiophosphinic chloride with substituted anili... more The nucleophilic substitution reactions of diethyl thiophosphinic chloride with substituted anilines (XC 6 H 4 NH 2) and deuterated anilines (XC 6 H 4 ND 2) are investigated kinetically in acetonitrile at 55.0 o C. The values of deuterium kinetic isotope effects (DKIEs; k H /k D) invariably increase from secondary inverse (k H /k D < 1) to primary normal (k H /k D > 1) as the nucleophiles change from the strongly basic to weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the gradual transition state (TS) variation from a predominant backside attack, via invariably increasing the fraction of a frontside attack, to a predominant frontside attack, in which the reaction mechanism is a concerted S N 2 pathway. A frontside attack involving a hydrogen bonded, four-center-type TS is substantiated by the primary normal DKIEs.
PLOS ONE, 2015
The Vibrio cholerae N-acetyl glucosamine-binding protein A (GbpA) is a chitin-binding protein inv... more The Vibrio cholerae N-acetyl glucosamine-binding protein A (GbpA) is a chitin-binding protein involved in V. cholerae attachment to environmental chitin surfaces and human intestinal cells. We previously investigated the distribution and genetic variations of gbpA in a large collection of V. cholerae strains and found that the gene is consistently present and highly conserved in this species. Primers and probe were designed from the gbpA sequence of V. cholerae and a new Taq-based qPCR protocol was developed for diagnostic detection and quantification of the bacterium in environmental and stool samples. In addition, the positions of primers targeting the gbpA gene region were selected to obtain a short amplified fragment of 206 bp and the protocol was optimized for the analysis of formalinfixed samples, such as historical Continuous Plankton Recorder (CPR) samples. Overall, the method is sensitive (50 gene copies), highly specific for V. cholerae and failed to amplify strains of the closely-related species Vibrio mimicus. The sensitivity of the assay applied to environmental and stool samples spiked with V. cholerae ATCC 39315 was comparable to that of pure cultures and was of 10 2 genomic units/l for drinking and seawater samples, 10 1 genomic units/g for sediment and 10 2 genomic units/g for bivalve and stool samples. The method also performs well when tested on artificially formalin-fixed and degraded genomic samples and was able to amplify V. cholerae DNA in historical CPR samples, the earliest of which date back to August 1966. The detection of V. cholerae in CPR samples collected in cholera endemic areas such as the Benguela Current Large Marine Ecosystem (BCLME) is of particular significance and represents a proof of concept for the possible use of the CPR technology and the developed qPCR assay in cholera studies.
Deep Sea Research Part II: Topical Studies in Oceanography, 1993
The abundance, distribution, size, biomass, growth and grazing-induced mortality of phycoerythrin... more The abundance, distribution, size, biomass, growth and grazing-induced mortality of phycoerythrin (PE) rich chrococcoid cyanobacteria were studied during September-October 1986 in the Arabian Sea, the Gulf of Oman and the monsoonal upwelling region off the South East Arabian ...
Nature, 1991
ATMOSPHERIC concentrations of methane, an important greenhouse gas, have increased significantly ... more ATMOSPHERIC concentrations of methane, an important greenhouse gas, have increased significantly over the past few decades 1, 2. Although attention has been focused on anthropogenic sources, data from ice cores show that large changes in atmospheric ...
Advances in Marine Biology
... Similarly, it is impera-tive that C02 is removed from the combustion products since C02 will ... more ... Similarly, it is impera-tive that C02 is removed from the combustion products since C02 will &quot; crack&quot; to CO+ in the mass-spectrometer and will be detected at m/z 29. ... Natural variations in the absolute abundance of 14N and 15N occur at the 10~ 3 atom % level. ...
J Mass Spectrometry, 1985
Stable isotope tracer methods are gaining popularity in many fields, including environmental scie... more Stable isotope tracer methods are gaining popularity in many fields, including environmental science, agriculture and medicine. This is particularly true in the clinical sciences, where the use of radioisotopes can be precluded on ethical grounds and I3C and "N tracers are being used more frequently for metabolic studies. Mass spectrometry is the preferred technique for isotope analysis. Sample preparation techniques for classical isotope ratio mass spectrometry are often tedious and can involve the use of complex vacuum apparatus that is quite foreign to the biological chemist. Organic gas chromatography/mass spectrometry (GUMS) overcomes many sample preparation problems but may lack the performance needed for isotope analysis. This paper describes the analysis of I3C using an automatic elemental gas chromatograph interfaced to an isotope ratio mass spectrometer, a system which was developed initially for the analysis of "N. Details of the residual gas background, peak broadening due to high carrier gas pressures, mass spectral linearity and response to changing sample peak heights and variations of the measured isotope ratio with sample pressure are described. Sensitivity and performance data (reproducibility f 0.62% at natural abundance) are also given. The potential of this system for other gas chromatographic applications, automatic data handling and the possible simultaneous analysis of "C and "N are also discussed.