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Modeling of microorganisms transport in a cylindrical pore Texte intégral
2008
A mathematical model accounting for key parameters as microbial propagation, metabolite formation, dispersion, microbial chemotaxis and water flooding has been proposed to simulate the transport of microorganisms and their metabolites in a cylindrical pore with oil adhered to its inside surface. The model focuses on the transport and the concentration distributions of microorganisms and their metabolites in the cylindrical pore, especially the concentrations that on the oil-water interface. Results from the present model indicate that microorganisms and their metabolites assembled on the oil-water interface during the water flooding process, and the concentration gradients of microorganisms and their metabolites from the pore center region up to the oil-water interface in radial direction of the cylindrical pore were consequently formed. Equilibrium concentrations of microorganisms and their metabolites in the cylindrical pore were obtained when water flow rate within a certain scope, and there existed a critical water flow rate at which the maximum equilibrium concentration of microorganisms on the oil-water interface was developed. Investigations carried out in this study may provide better understanding on the transport mechanism of microorganisms in porous media.
Afficher plus [+] Moins [-]Microorganisms in Daqu: a starter culture of Chinese Maotai-flavor liquor Texte intégral
2008
Wang, Chang-lu | Shi, Dong-jian | Gong, Guo-li
Maotai-flavor liquor, a famous traditional Chinese drink, is distilled from fermented sorghum in the southern province of China. Moreover, it is of interest as one of the few examples of liquor distilled from the product of a fermentation using a wild microflora starter. Daqu is the starter of this fermentation process. Daqu is a mixture of two components: milled wheat and a complex microbial community. The composition and the effects of this microbial group are largely unknown. In this study, we have analysed the constituents of the microbial community and the development of microorganisms in the industrial Daqu preparation and ripening process. More than 200 colonies were isolated and characterized. The isolates were discriminated by phenotypic and conventional biochemical taxonomic methods. The results revealed the presence of bacteria, moulds and yeasts. Bacteria consist of Bacillus, Acetobacter, Lactobacillus, and Clostridium, among which Bacillus strains were found to be predominant. Moulds consisted of Aspergillus, Mucor, Rhizopus, Monascus and Trichoderma, and Aspergillus strains were found to be predominant in the six different biotypes. Yeasts comprised Saccharomyces, Hansenula, Candida, Pichia, and Torulaspora. The most frequently isolated yeasts belonged to the genus Saccharomyces. The microbial diversity shift showed that the microbial genera changed with increasing ripening time. Knowledge of the microbial diversity in Daqu provides a basis for microflora management and understanding of the role of microbes in the Daqu production process, and the contribution of Daqu performed as a starter culture to Maotai-flavor liquor.
Afficher plus [+] Moins [-]Contaminants and microorganisms in Dutch organic food products: a comparison with conventional products Texte intégral
2008
Hoogenboom, L.A.P. | Bokhorst, J.G. | Northolt, M.D. | Vijver, L.P.L van de | Broex, N.J.G. | Mevius, D.J. | Meijs, J.A.C. | Roest, J van der
Contaminants and microorganisms in Dutch organic food products: a comparison with conventional products Texte intégral
2008
Hoogenboom, L.A.P. | Bokhorst, J.G. | Northolt, M.D. | Vijver, L.P.L van de | Broex, N.J.G. | Mevius, D.J. | Meijs, J.A.C. | Roest, J van der
Organic products were analysed for the presence of contaminants, microorganisms and antibiotic resistance and compared with those from conventional products. No differences were observed in the Fusarium toxins deoxynivalenol and zearalenone in organic and conventional wheat, during both a dry period and a very wet period which promoted the production of these toxins. Nitrate levels in head lettuce produced organically in the open field were much lower than those in conventional products. In iceberg lettuce and head lettuce from the greenhouse, no differences were detected. Organically produced carrots contained higher nitrate levels than conventional products. Both organic and conventional products contained no residues of non-polar pesticides above the legal limits, although some were detected in conventional lettuce. Organic products contained no elevated levels of heavy metals. Salmonella was detected in 30% of pig faeces samples obtained from 30 organic farms, similar to the incidence at conventional farms. At farms that switched to organic production more then 6 years ago no Salmonella was detected, with the exception of one stable with young pigs recently purchased from another farm. No Salmonella was detected in faeces at the nine farms with organic broilers, and at one out of ten farms with laying hens. This is comparable with conventional farms where the incidence for Salmonella lies around 10%. Campylobacter was detected in faeces at all organic broiler farms, being much higher than at conventional farms. One of the most remarkable results was the fact that faeces from organic pigs and broilers showed a much lower incidence of antibiotic resistant bacteria, except for Campylobacter in broilers. It is concluded that the organic products investigated scored as equally well as conventional products with regard to food safety and at the same time show some promising features with respect to antibiotic resistance.
Afficher plus [+] Moins [-]Contaminants and micro-organisms in Dutch organic food products; comparison with conventional products Texte intégral
2008
Hoogenboom, Ron Laurentius | Bokhorst, Jan G. | Northolt, Martin D. | Van De Vijver, Lucy | Broex, Nico J.G. | Mevius, Dik J. | Meijs, Jac A.C. | Van Der Roest, Joop
Organic products were analysed for the presence of contaminants, micro-organisms and antibiotic resistance and compared with those from conventional products. No differences were observed in the Fusarium toxins deoxynivalenol and zearalenone in organic and conventional wheat, both during a dry period and a very wet period promoting the production of these toxins. Nitrate levels in head lettuce produced organically in the open field were much lower than those in conventional products. In iceberg lettuce and head lettuce from the green house no differences were detected. Organically produced carrots contained higher nitrate levels than conventional products. Both organic and conventional products contained no residues of non-polar pesticides above the legal limits, although some were detected in conventional lettuce. Organic products contained no elevated levels of heavy metals. Salmonella was detected in 30% of pig faeces samples obtained from 30 organic farms, similar to the incidence at conventional farms. At farms that switched to organic production more then 6 years ago, no Salmonella was detected, with the exception of one stable with young pigs recently purchased from another farm. No Salmonella was detected in faeces at the nine farms with organic broilers, and at one out of 10 farms with laying hens. This is comparable to conventional farms where the incidence for Salmonella lies around 10%. Campylobacter was detected in faeces at all organic broiler farms, being much higher than at conventional farms. One of the most remarkable results was the fact that faeces from organic pigs and broilers showed a much lower incidence of antibiotic resistant bacteria, except for Campylobacter in broilers. It is concluded that the organic products investigated scored equally good as conventional products with regard to food safety and at the same time show some promising features with respect to antibiotic resistance.
Afficher plus [+] Moins [-]Genetic Diversity of Eukaryotic Microorganisms in Lake Taihu, a Large Shallow Subtropical Lake in China Texte intégral
2008
Chen, Meijun | Chen, Feizhou | Yu, Yang | Ji, Jian | Kong, Fanxiang
We investigated the genetic diversity of eukaryotic microorganisms (0.8-20 μm) by sequencing cloned 18S rRNA genes in six genetic libraries constructed from six locations in Lake Taihu, a large shallow subtropical lake in China. Genetic libraries of eukaryotic ribosomal RNA were screened by restriction fragment length polymorphism (RFLP) analysis, and one clone representative of each RFLP pattern was partially sequenced. A total of 528 clones were clustered into 165 RFLP patterns and finally into 131 operational taxonomic unit (OTUs). Phylogenetic analysis revealed that each library included many unique OTUs, as well as members of distantly related phylogenetic groups. A majority of the clones were from alveolates, stramenopiles, cercozoa, cryptophytes, chlorophytes, and fungi, with members of choanoflagellida, euglenida, centroheliozoa, ancyromonadidae, ichthyosporea, and kathablepharid representing a minor fraction of the library. Six OTUs (15 clones) were not related to any known eukaryotic group. Canonical correspondence analysis suggested that the differences in eukaryotic microorganism community composition of in the six regions were partially related to trophic status, sediment resuspension, and top-down regulation by metazooplankton.
Afficher plus [+] Moins [-]Numeration methods for targeting photoactive materials in the UV-A photocatalytic removal of microorganisms Texte intégral
2008
Josset, Sébastien | Keller, Nicolas | Lett, Marie-Claire | Ledoux, Marc J. | Keller, Valérie
This tutorial review reports on the different numeration methods for evaluating the efficiency of the photocatalytic action on microorganisms. Here we put forward the advantages and drawbacks of the standard methods such as the plate count, the fluorescence techniques and the Most Probable Number method for determining the biocidal photocatalytic activity and thus selecting efficient photocatalytic materials among complex systems. We highlight that bacterial spores are a representative and suitable tool for meeting the restrictive requirements resulting from the complex use of living matter instead of chemical targets.
Afficher plus [+] Moins [-]Microbial communities and immigration in volcanic environments of Canary Islands (Spain) Texte intégral
2008
Portillo, M Carmen | Gonzalez, Juan M
Microbial communities and immigration in volcanic environments of Canary Islands (Spain) Texte intégral
2008
Portillo, M Carmen | Gonzalez, Juan M
Volcanic eruptions originated the Canary Islands (Spain), and today, different landscapes clearly show that active volcanism. The microbial communities present in these volcanic environments, both at high (above 70°C) and moderate (25-35°C) temperatures, were analyzed. Rock samples were processed using molecular techniques based on both DNA and RNA and complemented with the culture of microorganisms at a wide range of temperatures. Microorganisms detected through RNA-based molecular surveys were mostly related to mesophilic microorganisms, while representatives of hyperthermophiles were not detected. RNA decay curves at 80°C resulted in half-life estimates of less than 2 min for mesophilic microorganisms, supporting a recent and continuous arrival of microorganisms to the high temperature sampled sites. This study constitutes a unique experimental approach showing a great natural potential of microorganisms to spread out to different natural environments. The implications are of great interest for the biogeography, dispersal, and potential distribution of microorganisms, and their genetic information, in natural environments.
Afficher plus [+] Moins [-]High-pressure microbiology
2008
Michiels, Chris | Bartlett, Douglas Hoyt | Aertsen, Abram
To thrive under high pressure in the deep sea or terrestrial subsurface, microorganisms have evolved specific and unique adaptations. On the other hand, extreme pressure rapidly kills microorganisms, and pressurization is emerging as a promising technique for food preservation. Understanding the mechanisms behind microbial high pressure adaptation and inactivation provides insights into the most fundamental properties of living systems as compared to nonliving ones. This book moves from basic science to practical applications, explaining topics such as thermodynamic principles, piezophilic microorganisms, food preservation, nonpiezophilic microorganisms, and deep-biosphere and deep-sea microorganisms.
Afficher plus [+] Moins [-]Microbial communities and immigration in volcanic environments of Canary Islands (Spain) Texte intégral
2008
Portillo Guisado, María del Carmen | González Grau, Juan Miguel | Ministerio de Educación y Ciencia (España) | Consejo Superior de Investigaciones Científicas (España) | European Commission
Volcanic eruptions originated the Canary Islands (Spain), and today, different landscapes clearly show that active volcanism. The microbial communities present in these volcanic environments, both at high (above 70°C) and moderate (25–35°C) temperatures, were analyzed. Rock samples were processed using molecular techniques based on both DNA and RNA and complemented with the culture of microorganisms at a wide range of temperatures. Microorganisms detected through RNA-based molecular surveys were mostly related to mesophilic microorganisms, while representatives of hyperthermophiles were not detected. RNA decay curves at 80°C resulted in half-life estimates of less than 2 min for mesophilic microorganisms, supporting a recent and continuous arrival of microorganisms to the high temperature sampled sites. This study constitutes a unique experimental approach showing a great natural potential of microorganisms to spread out to different natural environments. The implications are of great interest for the biogeography, dispersal, and potential distribution of microorganisms, and their genetic information, in natural environments. | The authors acknowledge support through the projects REN2002-00041, CGL2004-03927-C02–01/BOS, and CGL2006-26198-E, from the Spanish Ministry of Education and Science, and a CSIC intramural project 200640I197. Participation of FEDER funds in this support is acknowledged. | Peer reviewed
Afficher plus [+] Moins [-]A simple filtration device for separating nonadherent microorganisms from mammalian cells in in vitro studies on microbial adherence Texte intégral
2008
Arseculeratne, Sarath N. | Sumathipala, Saranga | Eriyagama, Navaratne B.
In adherence studies, the removal of nonadherent microorganisms is essential for the valid enumeration of microorganisms that adhere to host cells. Although filtration devices are available commercially for the removal of nonadherent microorganisms, these are expensive and not reusable. In this article, we describe a simple, inexpensive, and reusable filtration device composed of two chambers of nylon, a nylon membrane of desired pore size, a rubber washer, and supporting stainless steel mesh. The device was effective in in vitro adherence assays for removing nonadherent endospores of Rhinosporidium seeberi from human buccal epithelial cells, providing valid counts of adherent microorganisms.
Afficher plus [+] Moins [-]A review of microbial injury and recovery methods in food [Erratum: 2008 Dec., v. 25, issue 8, p. 1001.] Texte intégral
2008
Wu, V.C.H.
The existence of injured microorganisms in food and their recovery during culturing procedures is critical. Microbial injury is characterized by the capability of a microorganism to return to normalcy during a resuscitation process in which the damaged essential components are repaired. Injury of microorganisms can be induced by sublethal heat, freezing, freeze-drying, drying, irradiation, high hydrostatic pressure, aerosolization, dyes, sodium azide, salts, heavy metals, antibiotics, essential oils, sanitizing compounds, and other chemicals or natural antimicrobial compounds. Injured microorganisms present a potential threat in food safety since they may repair themselves under suitable conditions. Detection of injured microorganisms can be important to practical interpretations of data in food microbiology. This review provides an overview of microbial injury in food and discusses the development of recovery methods for detecting injured foodborne microorganisms.
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