Gerald Gregori - Profile on Academia.edu (original) (raw)
Papers by Gerald Gregori
Extralobar Pulmonary Sequestration Presenting with Torsion and Associated Hydrothorax
European Journal of Pediatric Surgery, May 1, 2010
ABSTRACT Posterior mediastinal masses have widely variant presentations and a broad differential ... more ABSTRACT Posterior mediastinal masses have widely variant presentations and a broad differential diagnosis. We describe an adolescent boy presenting with a posterior mediastinal mass, associated with abdominal pain and pleural effusion. Radiologic, operative, and pathologic findings are reviewed. This patient was found to have torsion of an extralobar pulmonary sequestration, of which only 2 other cases have been reported in the literature. Although radiologic findings of a systemic arterial supply to the mass may be absent, with patients presenting with this constellation of symptoms, a high index of suspicion of a sequestration should be maintained.
Embo Rep, 2003
Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampere... more Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampered by difficulties in studying bacterial population heterogeneity. Using in situ detection of protein oxidation in single E. coli cells, and using a density-gradient centrifugation technique to separate culturable and non-culturable cells, we show that the proteins in non-culturable cells show increased and irreversible oxidative damage, which affects various bacterial compartments and proteins. The levels of expression of specific stress regulons are higher in non-culturable cells, confirming increased defects relating to oxidative damage and the occurrence of aberrant, such as by amino-acid misincorporation, proteins. Our data suggest that non-culturable cells are produced due to stochastic deterioration, rather than an adaptive programme, and pinpoint oxidation management as the 'Achilles heel' of these cells.
Appl Opt, 2006
Scatter of a two-dimensional Gaussian beam of a rectangular cross section by individual particles... more Scatter of a two-dimensional Gaussian beam of a rectangular cross section by individual particles suspended in a fluid in a cylindrical channel is modeled by using a full-wave approach. First, the internal and scattered fields associated with the cylindrical channel and the two-dimensional Gaussian beam are computed. The spatial variations of the computed electromagnetic field inside the channel indicate that particles and cells of sizes relevant to flow cytometry are subjected to essentially plane-wave illumination, and hence Lorenz-Mie theory is applicable for spherical particles. Further, it is assumed that the perturbation of the electromagnetic field in the channel that is due to the presence of a particle is negligible, allowing us to ignore the interactive scatter of the particle and the channel (they are electromagnetically uncoupled). This approximation is valid when the particle intercepts a small fraction of the total energy inside the channel and when the particle or cell has a low relative refractive index. Measurements of scatter from the channel agree with the analytical model and are used to determine the location of detectors to measure scatter from particles in the channel. Experimental results of accumulated scatter from single latex spheres flowing in the channel show good agreement with computed results, thereby validating the internal field and uncoupled scatter models.
PLOS ONE, 2015
Water safety is a major concern for public health and for natural environment preservation. We pr... more Water safety is a major concern for public health and for natural environment preservation. We propose to use bacteriophages to develop biosensor tools able to detect human and animal pathogens present in water. For this purpose, we take advantage of the highly discriminating properties of the bacteriophages, which specifically infect their bacterial hosts. The challenge is to use a fluorescent reporter protein that will be synthesized, and thus detected, only once the specific recognition step between a genetically modified temperate bacteriophage and its bacterial host has occurred. To ensure the accuracy and the execution speed of our system, we developed a test that does not require bacterial growth, since a simple 1-hour infection step is required. To ensure a high sensitivity of our tool and in order to detect up to a single bacterium, fluorescence is measured using a portable flow cytometer, also allowing on-site detection. In this study, we have constructed and characterized several "phagosensor" prototypes using the HK620 bacteriophage and its host Escherichia coli TD2158 and we successfully adapted this method to Salmonella detection. We show that the method is fast, robust and sensitive, allowing the detection of as few as 10 bacteria per ml with no concentration nor enrichment step. Moreover, the test is functional in sea water and allows the detection of alive bacteria. Further development will aim to develop phagosensors adapted on demand to the detection of any human or animal pathogen that may be present in water.
Automatic detection of retinal blood vessels is important to medical diagnoses and imaging. With ... more Automatic detection of retinal blood vessels is important to medical diagnoses and imaging. With the development of imaging technologies, various modals of retinal images are available. Few of currently published algorithms are applied to multimodal retinal images. Besides, the performance of algorithms with pathologies is expected to be improved. The purpose of this paper is to propose an automatic Ridge-Branch-Based
[Viability of heterotrophic bacteria in the Bay of Marseilles]
Comptes rendus biologies, 2003
Marine microorganism activities are commonly assessed by bulk methods and assigned to the total c... more Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such as assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214-218) has been adapted to resolve viable, damaged and dead cells in marine environments (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). The present reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features.
Near Real-Time in Situ Monitoring of Phytoplankton by Remote Flow Cytometry: Evidence of Sporadic Events on the Community Structure and Dynamics
A microencapsulation method based on flow cytometry technology
Le picoplancton photosynthétique
Les Biocides Des Revetements Antifouling Structurent-Ils Les Communautes Des Biofilms Les Colonisant: Etude Aux Differentes Saisons en Mediterranee et Dans L’Ocean Atlantique
Cytometry, 2001
The Bay of Marseilles is under the influence of a large urban concentration and its maritime acti... more The Bay of Marseilles is under the influence of a large urban concentration and its maritime activities. All of them discharge compounds (hydrocarbons, excess nutrients, heavy metals, chemicals, etc.) that can alter the marine ecosystem. To investigate whether ultraphytoplankton (Ͻ10 m) could be used as biosensors for their own ecosystem, a 2-year survey was conducted in the Bay of Marseilles. Methods: Seven stations monitored water mass and potential anthropic effects in the bay. Seawater samples were collected monthly or bimonthly at three depths, prefiltered, fixed, and kept in liquid nitrogen until flow cytometric analysis. Results: Five categories were created: Prochlorococcus, picoeukaryotes (Ͻ2 m), nanoeukaryotes I (2-6 m), nanoeukaryotes II (6 -10 m), and Synechococcus (Ͻ1.5 m). Artificial neural network analysis (Kohonen self-organizing maps) produced the same number of clusters as cluster analysis with Winlist software (Verity Software House). Conclusions: In addition to the wide variabilities in abundance and biomass, there were a strong seasonal signal and sporadic events. Lessons are derived from this study for future monitoring of marine microorganisms. Cytometry 44: [247][248][249][250][251][252][253][254][255][256] 2001.
An annual survey of bacterial production, respiration and ectoenzyme activity in coastal NW Mediterranean waters: temperature and resource controls
Environ Sci Pollut Res Int, 2014
We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosph... more We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosphatase activity (phos) and ectoaminopeptidase activity (prot) in relation to biogeochemical parameters, nutritive resources and in situ temperature over a 1-year survey at the long-term observatory the SOLEMIO station (Marseille bay, NW Mediterranean Sea). Despite its proximity to the coast, oligotrophic conditions prevailed at this station (yearly mean of Chl a = 0.43 μg dm(-3), NO3 = 0.55 μmol dm(-3) and PO4 = 0.04 μmol dm(-3)). Episodic meteorological events (dominant winds, inputs from the Rhone River) induced rapid oscillations (within 15 days) in temperature and sometimes salinity that resulted in rapid changes in phytoplankton succession and a high variability in C/P ratios within the particulate and dissolved organic matter. Throughout the year, BP ranged from 0.01 to 0.82 μg C dm-(3) h-(1) and bacterial growth efficiency varied from 1 to 39 %, with higher values in summer. Enrichment experiments showed that BP was limited most of the year by phosphorus availability (except in winter). A significant positive correlation was found between in situ temperature, BP, BR and phos. Finally, we found that temperature and phosphate availability were the main factors driving heterotrophic bacterial activity and thus play a fundamental role in carbon fluxes within the marine ecosystem.
Onset of the spring bloom in the northwestern Mediterranean Sea: influence of environmental pulse events on the in situ hourly-scale dynamics of the phytoplankton community structure
Frontiers in microbiology, 2014
Most of phytoplankton influence is barely understood at the sub meso scale and daily scale becaus... more Most of phytoplankton influence is barely understood at the sub meso scale and daily scale because of the lack of means to simultaneously assess phytoplankton functionality, dynamics and community structure. For a few years now, it has been possible to address this objective with an automated in situ high frequency sampling strategy. In order to study the influence of environmental short-term events (nutrients, wind speed, precipitation, solar radiation, temperature, and salinity) on the onset of the phytoplankton bloom in the oligotrophic Bay of Villefranche-sur-Mer (NW Mediterranean Sea), a fully remotely controlled automated flow cytometer (CytoSense) was deployed on a solar-powered platform (EOL buoy, CNRS-Mobilis). The CytoSense carried out single-cell analyses on particles (1-800 μm in width, up to several mm in length), recording optical pulse shapes when analyzing several cm(3). Samples were taken every 2 h in the surface waters during 2 months. Up to 6 phytoplankton cluster...
Possible bloom of free trichomes in the Bay of Marseille, NW Mediterranean Sea: an anomaly evidenced by flow cytometry
Journal of Plankton Research, 2012
Journal of Plankton Research, 2007
Phytoplankton observation is the product of a number of trade-offs related to sampling processes,... more Phytoplankton observation is the product of a number of trade-offs related to sampling processes, required level of diversity and size spectrum analysis capabilities of the techniques involved. Instruments combining the morphological and high-frequency analysis for phytoplankton cells are now available. This paper presents an application of the automated high-resolution flow cytometer Cytosub as a tool for analysing phytoplanktonic cells in their natural environment. High resolution data from a temporal study in the Bay of Marseille (analysis every 30 min over 1 month) and a spatial study in the Southern Indian Ocean (analysis every 5 min at 10 knots over 5 days) are presented to illustrate the capabilities and limitations of the instrument. Automated high-frequency flow cytometry revealed the spatial and temporal variability of phytoplankton in the size range 12$50 mm that could not be resolved otherwise. Due to some limitations (instrumental memory, volume analysed per sample), recorded counts could be statistically too low. By combining high-frequency consecutive samples, it is possible to decrease the counting error, following Poisson's law, and to retain the main features of phytoplankton variability. With this technique, the analysis of phytoplankton variability combines adequate sampling frequency and effective monitoring of community changes.
Journal of Clinical Virology, 2009
Extremophiles, 2011
Here, we combined flow cytometry (FCM) and phylogenetic analyses after cell sorting to characteri... more Here, we combined flow cytometry (FCM) and phylogenetic analyses after cell sorting to characterize the dominant groups of the prokaryotic assemblages inhabiting two ponds of increasing salinity: a crystallizer pond (TS) with a salinity of 390 g/L, and the non-crystallizer pond (M1) with a salinity of 200 g/L retrieved from the solar saltern of Sfax in Tunisia. As expected, FCM analysis enabled the resolution of high nucleic acid content (HNA) and low nucleic acid content (LNA) prokaryotes. Next, we performed a taxonomic analysis of the bacterial and archaeal communities comprising the two most populated clusters by phylogenetic analyses of 16S rRNA gene clone library. We show for the first time that the presence of HNA and LNA content cells could also be extended to the archaeal populations. Archaea were detected in all M1 and TS samples, whereas representatives of Bacteria were detected only in LNA for M1 and HNA for TS. Although most of the archaeal sequences remained undetermined, other clones were most frequently affiliated to Haloquadratum and Halorubrum. In contrast, most bacterial clones belonged to the Alphaproteobacteria class (Phyllobacterium genus) in M1 samples and to the Bacteroidetes phylum (Sphingobacteria and Salinibacter genus) in TS samples.
EMBO reports, 2003
Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampere... more Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampered by difficulties in studying bacterial population heterogeneity. Using in situ detection of protein oxidation in single E. coli cells, and using a density-gradient centrifugation technique to separate culturable and non-culturable cells, we show that the proteins in non-culturable cells show increased and irreversible oxidative damage, which affects various bacterial compartments and proteins. The levels of expression of specific stress regulons are higher in non-culturable cells, confirming increased defects relating to oxidative damage and the occurrence of aberrant, such as by amino-acid misincorporation, proteins. Our data suggest that non-culturable cells are produced due to stochastic deterioration, rather than an adaptive programme, and pinpoint oxidation management as the 'Achilles heel' of these cells.
Comptes Rendus Biologies, 2003
Reçu le 13 mai 2003 ; accepté le 30 juillet 2003 Présenté par Lucien Laubier Résumé L'activité de... more Reçu le 13 mai 2003 ; accepté le 30 juillet 2003 Présenté par Lucien Laubier Résumé L'activité des micro-organismes marins est généralement mesurée globalement et rapportée au dénombrement total des cellules. La présence en quantités significatives de cellules mortes ou endommagées rend cette affectation incorrecte. Une technique de double marquage des acides nucléiques de bactéries dulçaquicoles (Barbesti et al., Cytometry 40 (2000) 214-218) a été adaptée pour les bactéries marines afin de quantifier séparément les cellules viables, endommagées et mortes (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). Cet article présente la première mise en oeuvre de cette approche, réalisée dans la baie de Marseille en périodes hivernale et printanière, sur deux sites aux caractéristiques très contrastées. Pour citer cet article : G. Grégori et al., C. R. Biologies 326 (2003). 2003 Publié par Éditions scientifiques et médicales Elsevier SAS pour l'Académie des sciences. Abstract Viability of heterotrophic bacteria in the Bay of Marseilles. Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such an assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214-218) has been adapted to resolve viable, damaged and dead cells in marine environments (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). The present paper reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features.
Extralobar Pulmonary Sequestration Presenting with Torsion and Associated Hydrothorax
European Journal of Pediatric Surgery, May 1, 2010
ABSTRACT Posterior mediastinal masses have widely variant presentations and a broad differential ... more ABSTRACT Posterior mediastinal masses have widely variant presentations and a broad differential diagnosis. We describe an adolescent boy presenting with a posterior mediastinal mass, associated with abdominal pain and pleural effusion. Radiologic, operative, and pathologic findings are reviewed. This patient was found to have torsion of an extralobar pulmonary sequestration, of which only 2 other cases have been reported in the literature. Although radiologic findings of a systemic arterial supply to the mass may be absent, with patients presenting with this constellation of symptoms, a high index of suspicion of a sequestration should be maintained.
Embo Rep, 2003
Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampere... more Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampered by difficulties in studying bacterial population heterogeneity. Using in situ detection of protein oxidation in single E. coli cells, and using a density-gradient centrifugation technique to separate culturable and non-culturable cells, we show that the proteins in non-culturable cells show increased and irreversible oxidative damage, which affects various bacterial compartments and proteins. The levels of expression of specific stress regulons are higher in non-culturable cells, confirming increased defects relating to oxidative damage and the occurrence of aberrant, such as by amino-acid misincorporation, proteins. Our data suggest that non-culturable cells are produced due to stochastic deterioration, rather than an adaptive programme, and pinpoint oxidation management as the 'Achilles heel' of these cells.
Appl Opt, 2006
Scatter of a two-dimensional Gaussian beam of a rectangular cross section by individual particles... more Scatter of a two-dimensional Gaussian beam of a rectangular cross section by individual particles suspended in a fluid in a cylindrical channel is modeled by using a full-wave approach. First, the internal and scattered fields associated with the cylindrical channel and the two-dimensional Gaussian beam are computed. The spatial variations of the computed electromagnetic field inside the channel indicate that particles and cells of sizes relevant to flow cytometry are subjected to essentially plane-wave illumination, and hence Lorenz-Mie theory is applicable for spherical particles. Further, it is assumed that the perturbation of the electromagnetic field in the channel that is due to the presence of a particle is negligible, allowing us to ignore the interactive scatter of the particle and the channel (they are electromagnetically uncoupled). This approximation is valid when the particle intercepts a small fraction of the total energy inside the channel and when the particle or cell has a low relative refractive index. Measurements of scatter from the channel agree with the analytical model and are used to determine the location of detectors to measure scatter from particles in the channel. Experimental results of accumulated scatter from single latex spheres flowing in the channel show good agreement with computed results, thereby validating the internal field and uncoupled scatter models.
PLOS ONE, 2015
Water safety is a major concern for public health and for natural environment preservation. We pr... more Water safety is a major concern for public health and for natural environment preservation. We propose to use bacteriophages to develop biosensor tools able to detect human and animal pathogens present in water. For this purpose, we take advantage of the highly discriminating properties of the bacteriophages, which specifically infect their bacterial hosts. The challenge is to use a fluorescent reporter protein that will be synthesized, and thus detected, only once the specific recognition step between a genetically modified temperate bacteriophage and its bacterial host has occurred. To ensure the accuracy and the execution speed of our system, we developed a test that does not require bacterial growth, since a simple 1-hour infection step is required. To ensure a high sensitivity of our tool and in order to detect up to a single bacterium, fluorescence is measured using a portable flow cytometer, also allowing on-site detection. In this study, we have constructed and characterized several "phagosensor" prototypes using the HK620 bacteriophage and its host Escherichia coli TD2158 and we successfully adapted this method to Salmonella detection. We show that the method is fast, robust and sensitive, allowing the detection of as few as 10 bacteria per ml with no concentration nor enrichment step. Moreover, the test is functional in sea water and allows the detection of alive bacteria. Further development will aim to develop phagosensors adapted on demand to the detection of any human or animal pathogen that may be present in water.
Automatic detection of retinal blood vessels is important to medical diagnoses and imaging. With ... more Automatic detection of retinal blood vessels is important to medical diagnoses and imaging. With the development of imaging technologies, various modals of retinal images are available. Few of currently published algorithms are applied to multimodal retinal images. Besides, the performance of algorithms with pathologies is expected to be improved. The purpose of this paper is to propose an automatic Ridge-Branch-Based
[Viability of heterotrophic bacteria in the Bay of Marseilles]
Comptes rendus biologies, 2003
Marine microorganism activities are commonly assessed by bulk methods and assigned to the total c... more Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such as assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214-218) has been adapted to resolve viable, damaged and dead cells in marine environments (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). The present reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features.
Near Real-Time in Situ Monitoring of Phytoplankton by Remote Flow Cytometry: Evidence of Sporadic Events on the Community Structure and Dynamics
A microencapsulation method based on flow cytometry technology
Le picoplancton photosynthétique
Les Biocides Des Revetements Antifouling Structurent-Ils Les Communautes Des Biofilms Les Colonisant: Etude Aux Differentes Saisons en Mediterranee et Dans L’Ocean Atlantique
Cytometry, 2001
The Bay of Marseilles is under the influence of a large urban concentration and its maritime acti... more The Bay of Marseilles is under the influence of a large urban concentration and its maritime activities. All of them discharge compounds (hydrocarbons, excess nutrients, heavy metals, chemicals, etc.) that can alter the marine ecosystem. To investigate whether ultraphytoplankton (Ͻ10 m) could be used as biosensors for their own ecosystem, a 2-year survey was conducted in the Bay of Marseilles. Methods: Seven stations monitored water mass and potential anthropic effects in the bay. Seawater samples were collected monthly or bimonthly at three depths, prefiltered, fixed, and kept in liquid nitrogen until flow cytometric analysis. Results: Five categories were created: Prochlorococcus, picoeukaryotes (Ͻ2 m), nanoeukaryotes I (2-6 m), nanoeukaryotes II (6 -10 m), and Synechococcus (Ͻ1.5 m). Artificial neural network analysis (Kohonen self-organizing maps) produced the same number of clusters as cluster analysis with Winlist software (Verity Software House). Conclusions: In addition to the wide variabilities in abundance and biomass, there were a strong seasonal signal and sporadic events. Lessons are derived from this study for future monitoring of marine microorganisms. Cytometry 44: [247][248][249][250][251][252][253][254][255][256] 2001.
An annual survey of bacterial production, respiration and ectoenzyme activity in coastal NW Mediterranean waters: temperature and resource controls
Environ Sci Pollut Res Int, 2014
We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosph... more We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosphatase activity (phos) and ectoaminopeptidase activity (prot) in relation to biogeochemical parameters, nutritive resources and in situ temperature over a 1-year survey at the long-term observatory the SOLEMIO station (Marseille bay, NW Mediterranean Sea). Despite its proximity to the coast, oligotrophic conditions prevailed at this station (yearly mean of Chl a = 0.43 μg dm(-3), NO3 = 0.55 μmol dm(-3) and PO4 = 0.04 μmol dm(-3)). Episodic meteorological events (dominant winds, inputs from the Rhone River) induced rapid oscillations (within 15 days) in temperature and sometimes salinity that resulted in rapid changes in phytoplankton succession and a high variability in C/P ratios within the particulate and dissolved organic matter. Throughout the year, BP ranged from 0.01 to 0.82 μg C dm-(3) h-(1) and bacterial growth efficiency varied from 1 to 39 %, with higher values in summer. Enrichment experiments showed that BP was limited most of the year by phosphorus availability (except in winter). A significant positive correlation was found between in situ temperature, BP, BR and phos. Finally, we found that temperature and phosphate availability were the main factors driving heterotrophic bacterial activity and thus play a fundamental role in carbon fluxes within the marine ecosystem.
Onset of the spring bloom in the northwestern Mediterranean Sea: influence of environmental pulse events on the in situ hourly-scale dynamics of the phytoplankton community structure
Frontiers in microbiology, 2014
Most of phytoplankton influence is barely understood at the sub meso scale and daily scale becaus... more Most of phytoplankton influence is barely understood at the sub meso scale and daily scale because of the lack of means to simultaneously assess phytoplankton functionality, dynamics and community structure. For a few years now, it has been possible to address this objective with an automated in situ high frequency sampling strategy. In order to study the influence of environmental short-term events (nutrients, wind speed, precipitation, solar radiation, temperature, and salinity) on the onset of the phytoplankton bloom in the oligotrophic Bay of Villefranche-sur-Mer (NW Mediterranean Sea), a fully remotely controlled automated flow cytometer (CytoSense) was deployed on a solar-powered platform (EOL buoy, CNRS-Mobilis). The CytoSense carried out single-cell analyses on particles (1-800 μm in width, up to several mm in length), recording optical pulse shapes when analyzing several cm(3). Samples were taken every 2 h in the surface waters during 2 months. Up to 6 phytoplankton cluster...
Possible bloom of free trichomes in the Bay of Marseille, NW Mediterranean Sea: an anomaly evidenced by flow cytometry
Journal of Plankton Research, 2012
Journal of Plankton Research, 2007
Phytoplankton observation is the product of a number of trade-offs related to sampling processes,... more Phytoplankton observation is the product of a number of trade-offs related to sampling processes, required level of diversity and size spectrum analysis capabilities of the techniques involved. Instruments combining the morphological and high-frequency analysis for phytoplankton cells are now available. This paper presents an application of the automated high-resolution flow cytometer Cytosub as a tool for analysing phytoplanktonic cells in their natural environment. High resolution data from a temporal study in the Bay of Marseille (analysis every 30 min over 1 month) and a spatial study in the Southern Indian Ocean (analysis every 5 min at 10 knots over 5 days) are presented to illustrate the capabilities and limitations of the instrument. Automated high-frequency flow cytometry revealed the spatial and temporal variability of phytoplankton in the size range 12$50 mm that could not be resolved otherwise. Due to some limitations (instrumental memory, volume analysed per sample), recorded counts could be statistically too low. By combining high-frequency consecutive samples, it is possible to decrease the counting error, following Poisson's law, and to retain the main features of phytoplankton variability. With this technique, the analysis of phytoplankton variability combines adequate sampling frequency and effective monitoring of community changes.
Journal of Clinical Virology, 2009
Extremophiles, 2011
Here, we combined flow cytometry (FCM) and phylogenetic analyses after cell sorting to characteri... more Here, we combined flow cytometry (FCM) and phylogenetic analyses after cell sorting to characterize the dominant groups of the prokaryotic assemblages inhabiting two ponds of increasing salinity: a crystallizer pond (TS) with a salinity of 390 g/L, and the non-crystallizer pond (M1) with a salinity of 200 g/L retrieved from the solar saltern of Sfax in Tunisia. As expected, FCM analysis enabled the resolution of high nucleic acid content (HNA) and low nucleic acid content (LNA) prokaryotes. Next, we performed a taxonomic analysis of the bacterial and archaeal communities comprising the two most populated clusters by phylogenetic analyses of 16S rRNA gene clone library. We show for the first time that the presence of HNA and LNA content cells could also be extended to the archaeal populations. Archaea were detected in all M1 and TS samples, whereas representatives of Bacteria were detected only in LNA for M1 and HNA for TS. Although most of the archaeal sequences remained undetermined, other clones were most frequently affiliated to Haloquadratum and Halorubrum. In contrast, most bacterial clones belonged to the Alphaproteobacteria class (Phyllobacterium genus) in M1 samples and to the Bacteroidetes phylum (Sphingobacteria and Salinibacter genus) in TS samples.
EMBO reports, 2003
Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampere... more Vibrio cholerae, become non-culturable during stasis. The analysis of such cells has been hampered by difficulties in studying bacterial population heterogeneity. Using in situ detection of protein oxidation in single E. coli cells, and using a density-gradient centrifugation technique to separate culturable and non-culturable cells, we show that the proteins in non-culturable cells show increased and irreversible oxidative damage, which affects various bacterial compartments and proteins. The levels of expression of specific stress regulons are higher in non-culturable cells, confirming increased defects relating to oxidative damage and the occurrence of aberrant, such as by amino-acid misincorporation, proteins. Our data suggest that non-culturable cells are produced due to stochastic deterioration, rather than an adaptive programme, and pinpoint oxidation management as the 'Achilles heel' of these cells.
Comptes Rendus Biologies, 2003
Reçu le 13 mai 2003 ; accepté le 30 juillet 2003 Présenté par Lucien Laubier Résumé L'activité de... more Reçu le 13 mai 2003 ; accepté le 30 juillet 2003 Présenté par Lucien Laubier Résumé L'activité des micro-organismes marins est généralement mesurée globalement et rapportée au dénombrement total des cellules. La présence en quantités significatives de cellules mortes ou endommagées rend cette affectation incorrecte. Une technique de double marquage des acides nucléiques de bactéries dulçaquicoles (Barbesti et al., Cytometry 40 (2000) 214-218) a été adaptée pour les bactéries marines afin de quantifier séparément les cellules viables, endommagées et mortes (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). Cet article présente la première mise en oeuvre de cette approche, réalisée dans la baie de Marseille en périodes hivernale et printanière, sur deux sites aux caractéristiques très contrastées. Pour citer cet article : G. Grégori et al., C. R. Biologies 326 (2003). 2003 Publié par Éditions scientifiques et médicales Elsevier SAS pour l'Académie des sciences. Abstract Viability of heterotrophic bacteria in the Bay of Marseilles. Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such an assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214-218) has been adapted to resolve viable, damaged and dead cells in marine environments (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). The present paper reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features.