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At least 487 records · Page 27Linked to original sources
PubMed1999

Vibrio cholerae intestinal population dynamics in the suckling mouse model of infection.

The suckling mouse has been used as a model to identify Vibrio cholerae intestinal colonization factors for over two decades, yet little is known about the location of recoverable organisms along the gastrointestinal (GI) tract following intragastric inoculation. In the present study, we determined the population dynamics of wild-type and avirulent mutant derivatives of both classical and El Tor biotype strains throughout the entire suckling mouse GI tract at various times after intragastric inoculation. Wild-type strains preferentially colonized the middle small bowel with a sharp demarcation between more proximal segments which had manyfold-fewer recoverable cells. Surprisingly, large and stable populations of viable cells were also recovered from the cecum and large bowel. Strains lacking toxin-coregulated pili (TCP(-)) were cleared from the small bowel; however, an El Tor TCP(-) strain colonized the cecum and large bowel almost as well as the wild-type strain. Strains lacking lipopolysaccharide O antigen (OA(-)) were efficiently cleared from the small bowel at early times but then showed net growth for the remainder of the infections. Moreover, large populations of the OA(-) strains were maintained in the large bowel. These results show that for the El Tor biotype neither TCP nor OA is required for colonization of the suckling mouse large bowel. Finally, similar percent recoveries of wild-type, TCP(-), and OA(-) strains from the small bowel at an early time after infection suggest that TCP and OA are not required for strains of either biotype to resist bactericidal mechanisms in the suckling mouse GI tract.

Animals↗
PubMed2001

Population Dynamics of Two Toluene Degrading Bacterial Species in a Contaminated Stream.

Toluene uptake by a benthic biofilm community was previously shown to vary seasonally from 0.03 m hr?1 in winter to 0.2 m hr?1 in summer in a solvent-contaminated stream of the Aberjona watershed. We used quantitative PCR to estimate the population dynamics of previously isolated species of toluene-degrading Xanthobacter autotrophicus and Mycobacterium sp. in both toluene-contaminated and uncontaminated reaches of the stream, and to estimate their relative roles in overall biodegradation rate. Quantification using specific 16S rDNA primers forX. autotrophicus and Mycobacterium sp. showed that populations of both species were much larger in the toluene-contaminated than the toluene-free reach, in agreement with earlier culture-based investigations. A relatively brief bloom of X. autotrophicus occurred in the contaminated reach in the summer, while Mycobacterium sp. populations occurred at elevated densities for more than 5 months. Calculations showed that Mycobacterium, previously thought to be less important than Xanthobacter in annual toluene degradation based on single time-point CFU estimates, appears actually more important because of this longer persistence.

Journal Article↗
PubMed2003

Population dynamics of Vibrio fischeri during infection of Euprymna scolopes.

The luminous bacterium Vibrio fischeri colonizes a specialized light-emitting organ within its squid host, Euprymna scolopes. Newly hatched juvenile squid must acquire their symbiont from ambient seawater, where the bacteria are present at low concentrations. To understand the population dynamics of V. fischeri during colonization more fully, we used mini-Tn7 transposons to mark bacteria with antibiotic resistance so that the growth of their progeny could be monitored. When grown in culture, there was no detectable metabolic burden on V. fischeri cells carrying the transposon, which inserts in single copy in a specific intergenic region of the V. fischeri genome. Strains marked with mini-Tn7 also appeared to be equivalent to the wild type in their ability to infect and multiply within the host during coinoculation experiments. Studies of the early stages of colonization suggested that only a few bacteria became associated with symbiotic tissue when animals were exposed for a discrete period (3 h) to an inoculum of V. fischeri cells equivalent to natural population levels; nevertheless, all these hosts became infected. When three differentially marked strains of V. fischeri were coincubated with juvenile squid, the number of strains recovered from an individual symbiotic organ was directly dependent on the size of the inoculum. Further, these results indicated that, when exposed to low numbers of V. fischeri, the host may become colonized by only one or a few bacterial cells, suggesting that symbiotic infection is highly efficient.

Animal Structures↗
PubMed2005

The HIV coreceptor switch: a population dynamical perspective.

Over the course of infection, the coreceptor usage of the HIV virus changes from a preference for CCR5 to a preference for CXCR4 in approximately 50% of infected individuals. The change in coreceptor usage is the result of the complex interaction of the viral population with various cell populations of the immune system. Although many of the molecular processes involved in viral attachment and entry have been resolved, the population dynamical mechanisms leading to the emergence of CXCR4-using HIV variants in some infected individuals are not yet understood. Here, we review various hypotheses that have been proposed to explain the change of HIV coreceptor usage in the course of infection, and conclude that any corroboration or rejection of these hypotheses requires a quantitative analysis of the interaction between the virus and immune cells.

Disease Progression↗
PubMed1997

Use of RAPD and 16S rDNA sequencing for the study of Lactobacillus population dynamics in natural whey culture.

The development of communities of the thermophilic microflora of natural whey culture for Parmigiano Reggiano cheese production was studied by means of molecular techniques. RAPD analysis facilitates the identification of the Lactobacillus strains involved in this microbial association and permitted the study of population dynamics during two cycles of whey fermentation. Analysis of RAPD fingerprints revealed the presence of four biotypes that dominate the whey fermentation process. Sequence analysis of 16S rDNA demonstrated that the strains isolated from whey belong to Lact. helveticus and Lact. delbrueckii ssp. lactis species.

Base Sequence↗
PubMed1980

Density-dependent selection in a random environment: An evolutionary process that can maintain stable population dynamics.

A theoretical analysis of natural selection is presented in which fitnesses depend on population density and randomly varying environmental processes. The theory is based on a general, heuristic analysis of a pair of coupled, nonlinear, stochastic difference equations that describe the joint dynamics of allele frequencies and population size. Four main conclusions emerge from the investigation of a particular class of models: (i) growth rates at low population densities tend to increase; (ii) individual selection, given sufficient genetic flexibility, will mold growth rates at higher densities so that in spite of i, stable deterministic population dynamics are maintained; (iii) "more fit" genotypes cannot be simply characterized-in particular, the mean population size need not be increased; and (iv) genetic polymorphisms can be maintained in both haploid and diploid organisms.

Journal Article↗
PubMed2002

Population dynamics of Tylodelphys destructor and Diplostomum mordax (Digenea: Diplostomidae) co-occurring in the brain of Patagonian silversides from Lake Pellegrini, Patagonia, Argentina.

Studies on infection patterns of diplostomid parasites in commercially exploited fishes have not been done in Patagonia (Argentina). The aim of this work was to study the population dynamics of two diplostomid species in the brain of patagonian silversides (Odontesthes hatchery), the interaction between them, and effect on health and physical condition of the hosts. Tylodelphys destructor and Diplostomum mordax metacercariae in the brain of Patagonian silversides in Lake Pellegrini were studied between January 1991 and February 1992. Tylodelphys destructor parasitized all silversides examined; prevalence of D. mordax varied between 7% and 100%. Mean intensity for T. destructor was 35-140 and for D. mordax was 3-49. Highest mean intensities of T. destructor coincided with the lowest mean intensities of D. mordax. Recruitment seems to occur from July-November for T. destructor and from April-June for D. mordax, revealing a temporal segregation with inverse patterns of infection and recruitment. Tylodelphys destructor has higher intensities in the brain of the older fish, whereas D. mordax did not, suggesting another type of segregation. There were no evidences of gross pathology. No covariation between abundance of larvae and condition factor, gonadosomatic index, and gut fullness was detected.

Animals↗
PubMed1998

Methanogenic population dynamics during start-up of anaerobic digesters treating municipal solid waste and biosolids.

An aggressive start-up strategy was used to initiate codigestion in two anaerobic, continuously mixed bench-top reactors at mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. The digesters were inoculated with mesophilic anaerobic sewage sludge and cattle manure and were fed a mixture of simulated municipal solid waste and biosolids in proportions that reflect U.S. production rates. The design organic loading rate was 3.1 kg volatile solids/m3/day and the retention time was 20 days. Ribosomal RNA-targeted oligonucleotide probes were used to determine the methanogenic community structure in the inocula and the digesters. Chemical analyses were performed to evaluate digester performance. The aggressive start-up strategy was successful for the thermophilic reactor, despite the use of a mesophilic inoculum. After a short start-up period (20 days), stable performance was observed with high gas production rates (1.52 m3/m3/day), high levels of methane in the biogas (59%), and substantial volatile solids (54%) and cellulose (58%) removals. In contrast, the mesophilic digester did not respond favorably to the start-up method. The concentrations of volatile fatty acids increased dramatically and pH control was difficult. After several weeks of operation, the mesophilic digester became more stable, but propionate levels remained very high. Methanogenic population dynamics correlated well with performance measures. Large fluctuations were observed in methanogenic population levels during the start-up period as volatile fatty acids accumulated and were subsequently consumed. Methanosaeta species were the most abundant methanogens in the inoculum, but their levels decreased rapidly as acetate built up. The increase in acetate levels was paralleled by an increase in Methanosarcina species abundance (up to 11.6 and 4.8% of total ribosomal RNA consisted of Methanosarcina species ribosomal RNA in mesophilic and thermophilic digesters, respectively). Methanobacteriaceae were the most abundant hydrogenotrophic methanogens in both digesters, but their levels were higher in the thermophilic digester.

Anaerobiosis↗
PubMed1998

Longer-term population dynamics of Gyrodactylus bullatarudis and G. turnbulli (Monogenea) on adult guppies (Poecilia reticulata) in 50-I experimental arenas.

Two suprapopulations of monogeneans, one each of Gyrodactylus bullatarudis and G. turnbulli, on two groups of ten experimentally infected adult guppies (Poecilia reticulata) were maintained separately in 50.1 aquaria and monitored over 210 days. The G. bullatarudis population had a pattern of initial growth, then a subsequent decline to extinction after 40 days. G. turnbulli, after initial population growth and decline, maintained low-intensity infections (0.33-3.3 parasites/host) on six hosts over 94 days and did not become extinct during the experiment. There were some differences between the host-site specificity of G. bullatarudis and G. turnbulli on adult P. reticulata as compared with previously observed infections on immature fish.

Aging↗
PubMed2007

Analysis of the origin and population dynamics of cardiac progenitor cells in a donor heart model.

Cardiac progenitor (stem) cells have recently been detected in and isolated from the myocardium of neonatal and adult mice, rats, and humans; however, the precise origin and characterization of these cells remain unclear. Using a heterotopic mouse heart transplantation model, we investigated the origin and population dynamics of cardiac progenitor cells. Donor hearts from wild-type C57/BL6 female mice were transplanted into green fluorescent protein (GFP)-transgenic C57/BL6 male mice. The donor hearts were collected 0, 2, 4, 8, and 12 weeks after transplantation. We used quantitative flow cytometry to analyze the number and origin of stem cells in the donor hearts and immunostaining to evaluate the time-related changes in their characteristics. Extracardiac GFP-positive stem cells immigrated into the donor hearts soon after transplantation. Immunostaining revealed that these GFP-positive stem cells in the donor hearts gradually lost expression of the hematopoietic markers of CD45 and CD34 and shifted to express the cardiac-specific transcription factors GATA-4 and NKx2.5. A few of the GFP-positive cells in the donor hearts finally acquired the mature cardiac phenotype in the absence of cell fusion with donor cardiomyocytes. Our discovery provides the first evidence that extracardiac stem cells may be of bone marrow origin, from which they can transform into cardiac progenitor cells in response to myocardial environment cues.

Animals↗
PubMed1994

Population dynamics of a Lac- strain of Escherichia coli during selection for lactose utilization.

During selection for lactose utilization, Lac+ revertants of FC40, a Lac- strain of Escherichia coli, appear at a high rate. Yet, no Lac+ revertants appear in the absence of lactose, or in its presence if the cells have another, unfulfilled requirement for growth. This study investigates more fully the population dynamics of FC40 when incubated in the absence of a carbon source or when undergoing selection for lactose utilization. In the absence of a carbon source, the viable cell numbers do not change over 6 days. When incubated in liquid lactose medium, Lac- cells do not undergo any measurable increase in numbers or in turbidity for at least 2 days. When FC40 is plated on lactose minimum medium in the presence of scavenger cells, the upper limit to the amount of growth of Lac- cells during 5 days is one doubling, and there is no evidence for turnover (i.e., a balance between growth and death). The presence of a minority population that could form microcolonies was not detected. The implications of these results, plus the fact that the appearance of Lac+ revertants during lactose selection is nearly constant with time, are discussed in reference to several models that have been postulated to account for adaptive mutations.

Alleles↗