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Polydextrose, Lactitol, and Fructo-Oligosaccharide Fermentation by Colonic Bacteria in a Three-Stage Continuous Culture System. Hollie M. Probert, 2004.In vitro fermentations were carried out by using a model of the human colon to simulate microbial activities of lower gut bacteria . Bacterial populations (and their metabolic products) were evaluated under the effects of various fermentable substrates . Carbohydrates tested were polydextrose, lactitol, and fructo-oligosaccharide (FOS) . Bacterial groups of interest were evaluated by fluorescence in situ hybridization as well as by species-specific PCR to determine bifidobacterial species and percent-G+C profiling of the bacterial communities present . Short-chain fatty acids (SCFA) produced during the fermentations were also evaluated . Polydextrose had a stimulatory effect upon colonic bifidobacteria at concentrations of 1 and 2% (using a single and pooled human fecal inoculum, respectively) . The bifidogenic effect was sustained throughout all three vessels of the in vitro system (P = 0.01 seen in vessel 3), as corroborated by the bacterial community profile revealed by %G+C analysis . This substrate supported a wide variety of bifidobacteria and was the only substrate where Bifidobacterium infantis was detected . The fermentation of lactitol had a deleterious effect on both bifidobacterial and bacteroides populations (P = 0.01) and decreased total cell numbers . SCFA production was stimulated, however, particularly butyrate (beneficial for host colonocytes) . FOS also had a stimulatory effect upon bifidobacterial and lactobacilli populations that used a single inoculum (P = 0.01 for all vessels) as well as a bifidogenic effect in vessels 2 and 3 (P = 0.01) when a pooled inoculum was used . A decrease in bifidobacteria throughout the model was reflected in the percent-G+C profiles . Comparative Analyses of the Complete Genome Sequences of Pierce's Disease and Citrus Variegated Chlorosis Strains of Xylella fastidiosa. M. A. Van Sluys, 2003.Xylella fastidiosa is a xylem-dwelling, insect-transmitted, gamma-proteobacterium that causes diseases in many plants, including grapevine, citrus, periwinkle, almond, oleander, and coffee . X . fastidiosa has an unusually broad host range, has an extensive geographical distribution throughout the American continent, and induces diverse disease phenotypes . Previous molecular analyses indicated three distinct groups of X . fastidiosa isolates that were expected to be genetically divergent . Here we report the genome sequence of X . fastidiosa (Temecula strain), isolated from a naturally infected grapevine with Pierce's disease (PD) in a wine-grape-growing region of California . Comparative analyses with a previously sequenced X . fastidiosa strain responsible for citrus variegated chlorosis (CVC) revealed that 98% of the PD X . fastidiosa Temecula genes are shared with the CVC X . fastidiosa strain 9a5c genes . Furthermore, the average amino acid identity of the open reading frames in the strains is 95.7% . Genomic differences are limited to phage-associated chromosomal rearrangements and deletions that also account for the strain-specific genes present in each genome . Genomic islands, one in each genome, were identified, and their presence in other X . fastidiosa strains was analyzed . We conclude that these two organisms have identical metabolic functions and are likely to use a common set of genes in plant colonization and pathogenesis, permitting convergence of functional genomic strategies . Online Monitoring of Escherichia coli Ghost Production. W. Haidinger, 2003.Controlled expression of cloned  X174 gene E in gram-negative bacteria results in lysis of the bacteria by the formation of a transmembrane tunnel structure built through the cell envelope complex . Production of bacterial ghosts is routinely monitored by classical microbiological procedures . These include determination of the turbidity of the culture and the total number of cells and the number of reproductive cells present during the time course of growth and lysis . Although conceptually simple, these methods are labor intensive and time consuming, providing a complete set of results after the determination of viable cell counts . To avoid culturing methods for bacterial growth, an alternative flow cytometric procedure is presented for the quantification of ghosts and polarized, as well as depolarized, nonlysed cells within a culture . For this method, which is based on the discriminatory power of the membrane potential-sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol, a staining protocol was developed and optimized for the maximum discrepancy in fluorescence between bacterial ghosts and viable cells . The total quantitative analysis procedure takes less than 2 min . The results derived from classical or cytometric analyses correlate with respect to the total cell numbers and the viability of the culture .
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