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Analysis and Validation of a Predictive Model for Growth and Death of Aeromonas hydrophila under Modified Atmospheres at Refrigeration Temperatures. Carmen Pin, 2004.Specific growth and death rates of Aeromonas hydrophila were measured in laboratory media under various combinations of temperature, pH, and percent CO2 and O2 in the atmosphere . Predictive models were developed from the data and validated by means of observations obtained from (i) seafood experiments set up for this purpose and (ii) the ComBase database (http://www.combase.cc; http://wyndmoor.arserrc.gov/combase/).Two main reasons were identified for the differences between the predicted and observed growth in food: they were the variability of the growth rates in food and the bias of the model predictions when applied to food environments . A statistical method is presented to quantitatively analyze these differences . The method was also used to extend the interpolation region of the model . In this extension, the concept of generalized Z values (C . Pin, G . García de Fernando, J . A . Ordóñez, and J . Baranyi, Food Microbiol. 18:539-545, 2001) played an important role . The extension depended partly on the density of the model-generating observations and partly on the accuracy of extrapolated predictions close to the boundary of the interpolation region . The boundary of the growth region of the organism was also estimated by means of experimental results for growth and death rates . Effects of Environmental Changes on Expression of the Oligopeptide Permease (opp) Genes of Borrelia burgdorferi. Xing-Guo Wang, 2002.We analyzed expression of a putative oligopeptide permease (Opp) of Borrelia burgdorferi. Unlike the opp operons of other bacteria for which there is a single substrate binding protein, B . burgdorferi codes for three substrate binding proteins (OppA-I to -III) in its opp operon and an additional two homologs on plasmids (OppA-IV and -V) . Instead of a single promoter region regulating transcription of the entire operon, as seen in other bacterial opp operons, it appears that among oppA-I, -II, and -III, as well as oppA-IV and -V, each has a potential upstream promoter region . We tested the function of these putative promoter sequences by fusion to a promoterless ß-galactosidase reporter gene in pCB182 . Each of the promoter regions was found to be active . The level of activity in the reporter constructs closely paralleled the level of expression of each gene in in vitro-grown B . burgdorferi . Changes in carbon and nitrogen availability differentially affected individual promoters, but no changes in promoter activity were seen when Escherichia coli bacteria (with the promoter constructs) were grown in various concentrations of phosphate and leucine and changes in pH . Expression of specific oppA genes with B . burgdorferi varied significantly between its mouse and fed and unfed tick hosts . Differences in regulation of opp gene expression suggest a potential role in environmental response by the organism . Quantitative Assessment of Picoeukaryotes in the Natural Environment by Using Taxon-Specific Oligonucleotide Probes in Association with Tyramide Signal Amplification-Fluorescence In Situ Hybridization and Flow Cytometry. Isabelle C. Biegala, 2003.Picoeukaryotes (cells of <3 µm in diameter) contribute significantly to marine plankton biomass and productivity, and recently molecular studies have brought to light their wide diversity . Among the methods that have been used so far to quantify aquatic microorganisms, fluorescence in situ hybridization of oligonucleotide probes combined with flow cytometry offers the advantages of both high resolution for taxonomic identification and automated cell counting . However, cell losses, cell clumps, and low signal-to-background ratio have often been mentioned as major problems for routine application of this combination of techniques . We developed a new protocol associating tyramide signal amplification-fluorescence in situ hybridization and flow cytometry, which allows the detection of picoeukaryotes in cultures during both the exponential and stationary phases . The use of surfactant and sonication proved to be essential for the detection and quantification of picoeukaryotes from the natural environment, with as little as a few tenths of a milliliter of 3-µm-pore-size prefiltered sea water . The routine application of the technique was tested along a coastal transect off Brittany (France), where the different groups of picoeukaryotes were investigated using already published specific probes and a newly designed probe that targets the order Mamiellales (Prasinophyceae, Chlorophyta) . Among the picoeukaryotes, Mamiellales outnumbered by 1 order of magnitude both the cyanobacteria and the non-Chlorophyta, which were represented mainly by the Pelagophyceae class . Picoeukaryote abundance increased from open toward more estuarine water, probably following changes in water temperature and stability .
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