On-line profiling of Escherichia coli stress response

in Communications in Agricultural and Applied Biological Sciences (in press)

On-line flow cytometry to detect cell growth rate and membrane damage during bioprocess: focus on the segregation of the microbial population

Conference (2013, April 24)

Flow-cytometric assessment of damages to Acetobacter senegalensis during freeze-drying process and storage

in Acetic acid bacteria journal (2013), volume 2(2(s1)), 10

Downstream processes have great influences on bacterial starter production. Different modifications occur to cellular compounds during freeze-drying process and storage of bacterial starters. Consequently ... [more ▼]

Downstream processes have great influences on bacterial starter production. Different modifications occur to cellular compounds during freeze-drying process and storage of bacterial starters. Consequently, viability and culturability (multiplication capacity) undergo some changes. In this study, the effects of freeze-drying process and storage conditions were examined on cell envelope integrity, respiration and culturability of Acetobacter senegalensis. Freezing of cells protected with mannitol (20% w/w) did not affect cell multiplication and respiration considerably; however, 19% of cells showed compromised cell envelope after freezing. After drying, 1.96×1011 CFU/g were enumerated, indicating that about 34% of the cells could survive and keep their culturability. Drying of the cells induced further leakage in cell envelope and finally 81% of cells appeared as injured ones; however, 87% of the dried cells maintained their respiration capacity. Storage temperature had significant effect on cell multiplication ability; higher storage temperature (35°C),caused 8.59-log reduction in cell culturability after nine-month period of storage. Collapse of cell envelop integrity and respiration wasobserved at 35°C. At lower storage temperature (4°C), the culturability decreased about one-log reduction after nine months. Cell envelope integrity was subjected to minor changes during a period of nine month-storage at 4°C whereas a heterogeneous population of cells with different respiration capacity emerged at 4°C. These results indicate that a major part of cells undergone drying process and storage entered into viable but non-culturable state. In addition, usage of different culture media didn’t improve resuscitation. Besides, it seems that sub-lethal damages to cell envelope caused uptake of propidium iodide, however these kinds of injuries could not impress cell multiplications and respiration. [less ▲]

What are the main metabolites responsible for the biocontrol potential of Bacillus strains ?

Poster (2013, February 08)

Decommissioned dates: chemical composition and fermentation substrate for the production of extracellular catalase by an Aspergillus phoenicis mutant

in Agriculture and Biology Journal of North America (2013)

The recovery of dates downgraded as a fermentation medium for the production of extracellular catalase by Aspergillus phoenicis K30 was studied. Analysis of the chemical composition of pulp and kernel ... [more ▼]

The recovery of dates downgraded as a fermentation medium for the production of extracellular catalase by Aspergillus phoenicis K30 was studied. Analysis of the chemical composition of pulp and kernel flour of dates showed that the pulp had a considerably greater carbohydrate content compared to the kernel (84 vs 2.93% respectively). However, the kernel flour was richer in nitrogen (0.68% vs 0.34), mineral elements (3.63 vs 1.28%) and in essential fatty acids C18: 2 vs C18: 3 than the pulp flour. The soluble extract of the date flour showed that sugars solubilised at 90% consisted of sucrose, fructose and glucose. Therefore, this extract, being an important source of carbon and energy, was used in the current study as a fermentation medium (after supplementation with 20% of corn steep) for the production of extracellular catalase by A. Phoenicis K30. During the course of this fermentation, the biomass was estimated at 18.6 g / L after 72 h of culture, while the maximum concentration of extracellular catalase (47.5 U / ml) was reached at 96 h of fermentation. The mycelium obtained in pellet form is suitable for industrial exploitation of this process. [less ▲]

Proteomic investigation of aphid honeydew reveals an unexpected diversity of proteins

in PLoS ONE (2013), Accepted pending revision

Real-time monitoring of cell viability and cell density on the basis of a three dimensional optical reflectance method (3D-ORM): investigation of the effect of sub-lethal and lethal injuries

in Journal of Industrial Microbiology & Biotechnology (2013)

Cell density and cell viability have been followed on-line by using a three-dimensional optical reflectance method (3D-ORM) probe. This method has allowed to highlight the differences between a well-mixed ... [more ▼]

Cell density and cell viability have been followed on-line by using a three-dimensional optical reflectance method (3D-ORM) probe. This method has allowed to highlight the differences between a well-mixed and a scale-down bioreactor configured in order to reproduce mixing deficiencies during a fed-batch culture of E. coli. These differences have been observed both for the obscuration factor (OBF) and the coincidence probability (COP) delivered by the probe. These parameters are correlated to flow cytometry measurement based on the PI-uptake test and cell density based on optical density measurement. This first set of results has pointed out the fact that the 3D-ORM probe is sensitive to sub-lethal injuries encountered by microbial cells in process-related conditions. The effect of lethal injuries has been further investigated on the basis of additional experiments involving heat stress and a sharp increase of the OBF has been observed indicating that cells are effectively injured by the increase of temperature. However, further improvement of the probe are needed in order to give access to single-cell measurements. [less ▲]

Flow-cytometric assessment of damages to Acetobacter senegalensis during freeze-drying process and storage

in Acetic Acid Bacteria (2013)

Downstream processes have great influences on bacterial starter production. Different modifications occur to cellular compounds during freeze-drying process and storage of bacterial starters. Consequently ... [more ▼]

Downstream processes have great influences on bacterial starter production. Different modifications occur to cellular compounds during freeze-drying process and storage of bacterial starters. Consequently, viability and culturability (multiplication capacity) undergo some changes. In this study, the effects of freeze-drying process and storage conditions were examined on cell envelope integrity, respiration and culturability of Acetobacter senegalensis. Freezing of cells protected with mannitol (20% w/w) did not affect cell multiplication and respiration considerably; however, 19% of cells showed compromised cell envelope after freezing. After drying, 1.96×1011 CFU/g were enumerated, indicating that about 34% of the cells could survive and keep their culturability. Drying of the cells induced further leakage in cell envelope and finally 81% of cells appeared as injured ones; however, 87% of the dried cells maintained their respiration capacity. Storage temperature had significant effect on cell multiplication ability; higher storage temperature (35°C) caused 8.59-log reduction in cell culturability after nine-month period of storage. Collapse of cell envelop integrity and respiration was observed at 35°C. At lower storage temperature (4°C), the culturability decreased about one-log reduction after nine months. Cell envelope integrity was subjected to minor changes during a period of nine month-storage at 4°C whereas a heterogeneous population of cells with different respiration capacity emerged at 4°C. These results indicate that a major part of cells undergone drying process and storage entered into viable but non-culturable state. In addition, usage of different culture media didn’t improve resuscitation. Besides, it seems that sub-lethal damages to cell envelope caused uptake of propidium iodide, however these kinds of injuries could not impress cell multiplications and respiration. [less ▲]

Improving effect of metal and oxide nanoparticles encapsulated in porous silica on fermentative biohydrogen production by Clostridium butyricum.

in Bioresource Technology (2013), 133C

This paper investigated the enhancement effect of nanometre-sized metallic (Pd, Ag and Cu) or metallic oxide (Fe(x)O(y)) nanoparticles on fermentative hydrogen production from glucose by a Clostridium ... [more ▼]

This paper investigated the enhancement effect of nanometre-sized metallic (Pd, Ag and Cu) or metallic oxide (Fe(x)O(y)) nanoparticles on fermentative hydrogen production from glucose by a Clostridium butyricum strain. These nanoparticles (NP) of about 2-3nm were encapsulated in porous silica (SiO(2)) and were added at very low concentration (10(-6)molL(-1)) in batch hydrogen production test. The cultures containing iron oxide NP produced 38% more hydrogen with a higher maximum H(2) production rate (HPR) of 58% than those without NP or with silica particles only. The iron oxide NP were used in a 2.5L sequencing-batch reactor and showed no significant effect on the yields (established at 2.2mol(hydrogen)mol(glucose)(-1)) but an improvement of the HPR (+113%, reaching a maximum HPR of 86mL(hydrogen)L(-1)h(-1)). These results suggest an improvement of the electron transfers trough some combinations between enzymatic activity and inorganic materials. [less ▲]

Termites as a tool to improve lignocellulose biomass valorization : study of enzymatic complex in termites and its common symbionts by comprehensive metabolite profiling

Conference (2012, November 16)