Biomedical subjects

Esther R Angert

Publications and source records attributed to Esther R Angert.

10 recordsLinked to original sources

PubMed2006

Surfaces of fluorinated pyridinium block copolymers with enhanced antibacterial activity.

Polystyrene-b-poly(4-vinylpyridine) copolymers were quaternized with 1-bromohexane and 6-perfluorooctyl-1-bromohexane. Surfaces prepared from these polymers were characterized by contact angle measurements, near-edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy. The fluorinated pyridinium surfaces showed enhanced antibacterial activity compared to their nonfluorinated counterparts. Even a polymer with a relatively low molecular weight pyridinium block showed high antimicrobial activity. The bactericidal effect was found to be related to the molecular composition and organization in the top 2-3 nm of the surface and increased with increasing hydrophilicity and pyridinium concentration of the surface.

Anti-Bacterial Agents↗

PubMed2006

Bionanofabrication of metallic and semiconductor nanoparticle arrays using S-layer protein lattices with different lateral spacings and geometries.

Two-dimensional (2-D) surface layer (S-layer) protein lattices isolated from the gram-positive bacterium Deinococcus radiodurans and the acidothermophilic archaeon Sulfolobus acidocaldarius were investigated and compared for their ability to biotemplate the formation of self-assembled, ordered arrays of inorganic nanoparticles (NPs). The NPs employed for these studies included citrate-capped gold NPs and various species of CdSe/ZnS core/shell quantum dots (QDs). The QD nanocrystals were functionalized with different types of thiol ligands (negative- or positive-charged/short- or long-chain length) in order to render them hydrophilic and thus water-soluble. Transmission electron microscopy, Fourier transform analyses, and pair correlation function calculations revealed that ordered nanostructured arrays with a range of spacings (approximately 7-22 nm) and different geometrical arrangements could be fabricated through the use of the two types of S-layers. These results demonstrate that it is possible to exploit the physicochemical/structural diversity of prokaryotic S-layer scaffolds to vary the morphological patterning of nanoscale metallic and semiconductor NP arrays.

Cadmium Compounds↗

PubMed2006

Assessment of biases associated with profiling simple, model communities using terminal-restriction fragment length polymorphism-based analyses.

Community profiles based on terminal-restriction fragment length polymorphism (T-RFLP) analyses of amplified ribosomal RNA genes are used to monitor changes in microbial community structure and are sometimes employed for semi-quantitative estimates of species richness and abundance in environmental samples. To assess the accuracy of T-RFLP community profiles representing the relative abundance of bacteria in a sample, five species of ruminal bacteria were used to construct simple "communities". Template DNA for PCR amplification was generated either by mixing equal quantities of genomic DNA from pure cultures or by mixing equal numbers of cells prior to DNA extraction. Pairwise mixtures of Fibrobacter succinogenes S85 with Ruminococcus albus 8, Ruminococcus flavefaciens FD-1, Butyrivibrio fibrisolvens 49 and Streptococcus bovis JB1 were created and a 5-member community was constructed. With genomic DNA mixes, relative abundance calculations based on T-RFLP patterns did not reflect input ratios. These discrepancies could not be accounted for by differences in genome size and rRNA operon copy number. In cell mixing experiments, easily lysed cells were overrepresented. To determine if a numerical correction factor could be used to compensate for observed discrepancies, we attempted to quantify biases attributed to DNA extraction and PCR amplification. Biases attributable to these factors led to deviations from expected PCR product ratios by 6% to 38%. We found that interactions were so complex that a suitable factor could not be derived. The unsystematic dependence of T-RFLP peak ratios on variability of DNA extraction and PCR amplification prevents accurate quantification of the relative abundance of microorganisms designed to represent simplified natural populations.

Bacteria↗

PubMed2006

Self-assembly of dendrimer-encapsulated nanoparticle arrays using 2-D microbial S-layer protein biotemplates.

We investigated the formation of self-assembled two-dimensional (2-D) arrays of dendrimer-encapsulated platinum nanoparticles (Pt-DENs) using prokaryotic surface-layer (S-layer) proteins as biomacromolecular templates. The Pt-DENs (mean core diameter 1.8 +/- 0.5 nm) were synthesized by chemical reduction of metal ion species complexed within the interior of fourth-generation, hydroxyl-terminated, starburst poly(amidoamine) dendrimers (G4 PAMAM-OH). Detailed structural and elemental composition analyses performed using high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy indicated that the dendrimer-metal nanocomposite particles were crystalline in nature rather than amorphous and that at least some quantity of the platinum found within the particles is present in the expected zerovalent state. By using the S-layer lattices from the acidothermophilic archaeon Sulfolobus acidocaldarius and the Gram-positive bacterium Deinococcus radiodurans as a biotemplate, hexagonal- and honeycomb-ordered arrays of the Pt-DENs were successfully fabricated under a range of different pH conditions via noncovalent nanoparticle-protein interactions. Fast Fourier transform analyses of transmission electron microscopy images verified that the fabricated Pt-DEN assemblies displayed mean periodicities that corresponded well with the lattice constants of the native protein templates (i.e., 22 and 18 nm for S. acidocaldarius and D. radiodurans S layers, respectively). Our results demonstrate that utilizing pre-synthesized Pt-DENs in conjunction with microbial S-layer proteins displaying highly periodic topochemical properties can be an effective, novel route for creating patterned arrays of Pt nanoparticles with potential technological applications.

Adsorption↗

PubMed2006

Fecal bacterial diversity in a wild gorilla.

We describe the bacterial diversity in fecal samples of a wild gorilla by use of a 16S rRNA gene clone library and terminal-restriction fragment length polymorphism (T-RFLP). Clones were classified as Firmicutes, Verrucomicrobia, Actinobacteria, Lentisphaerae, Bacteroidetes, Spirochetes, and Planctomycetes. Our data suggest that fecal populations did not change temporally, as determined by T-RFLP.

Animals↗

PubMed2005

Development of a strain-specific assay for detection of viable Lactobacillus sp. HOFG1 after application to cattle feed.

A strain-specific assay was developed for the detection of viable Lactobacillus on cattle feed. The DNA sequences of the 16S rRNA gene and four different 16S/23S rRNA intergenic spacer regions (ISR) from Lactobacillus sp. HOFG1 were determined. Based on these sequences, a strain-specific primer was designed for the amplification of one of the ISRs. When combined with a Lactobacillus group primer, the polymerase chain reaction (PCR) assay detected only Lactobacillus sp. HOFG1 and not other closely related L. animalis or L. murinus strains. The feed assay uses a combination of enrichment culturing and PCR to detect and enumerate viable Lactobacillus sp. HOFG1 after its application onto cattle feed. The high degree of primer specificity and use of selective culturing allows for the detection of viable Lactobacillus which is useful in tracking bacteria applied to complex feed mixtures that contain a high background of endogenous bacteria.

Animal Feed↗

PubMed2005

Alternatives to binary fission in bacteria.

Whereas most prokaryotes rely on binary fission for propagation, many species use alternative mechanisms, which include multiple offspring formation and budding, to reproduce. In some bacterial species, these eccentric reproductive strategies are essential for propagation, whereas in others the programmes are used conditionally. Although there are tantalizing images and morphological descriptions of these atypical developmental processes, none of these reproductive structures are characterized at the molecular genetic level. Now, with newly available analytical techniques, model systems to study these alternative reproductive programmes are being developed.

Bacteria↗

PubMed2005

Unwounded plants elicit Agrobacterium vir gene induction and T-DNA transfer: transformed plant cells produce opines yet are tumour free.

Agrobacterium tumefaciens is well known to cause crown gall tumours at plant wound sites and to benefit from this plant association by obtaining nutrients called opines that are produced by these tumours. Tumourigenesis requires expression of the vir regulon in response to chemical signals that are thought to be released from wound sites. Here, we examine chemical interactions between A. tumefaciens and unwounded plants. To determine whether unwounded plants can release significant amounts of vir gene inducers, we constructed an A. tumefaciens strain carrying a PvirB-gfp fusion. This fusion was strongly induced by co-culture with tobacco seedlings that have been germinated without any intentional wounding. The release of phenolic vir gene inducers was confirmed by GC/MS analysis. We also constructed a strain containing the gfp reporter located on an artificial T-DNA and expressed from a plant promoter. A. tumefaciens efficiently transferred this T-DNA into cells of unwounded plants in the absence of exogenous vir gene inducers. Many cells of seedlings colonized by the bacteria also produced octopine, which was detected using a Pocc-gfp reporter strain. This indicates transfer of the native T-DNA. However, these transformed plant cells did not form tumours. These results suggest that successful colonization of plants by A. tumefaciens, including T-DNA transfer and opine production, does not require wounding and does not necessarily cause cell proliferation. Transformation of plant cells without inciting tumours may represent a colonization strategy for this pathogen that has largely been overlooked.

Agrobacterium tumefaciens↗

PubMed2005

Nocturnal production of endospores in natural populations of epulopiscium-like surgeonfish symbionts.

Prior studies have described a morphologically diverse group of intestinal microorganisms associated with surgeonfish. Despite their diversity of form, 16S rRNA gene surveys and fluorescent in situ hybridizations indicate that these bacteria are low-G+C gram-positive bacteria related to Epulopiscium spp. Many of these bacteria exhibit an unusual mode of reproduction, developing multiple offspring intracellularly. Previous reports have suggested that some Epulopiscium-like symbionts produce dormant or phase-bright intracellular offspring. Close relatives of Epulopiscium, such as Metabacterium polyspora and Clostridium lentocellum, are endospore-forming bacteria, which raises the possibility that the phase-bright offspring are endospores. Structural evidence and the presence of dipicolinic acid demonstrate that phase-bright offspring of Epulopiscium-like bacteria are true endospores. In addition, endospores are formed as part of the normal daily life cycle of these bacteria. In the populations studied, mature endospores were seen only at night and the majority of cells in a given population produced one or two endospores per mother cell. Phylogenetic analyses confirmed the close relationship between the endospore-forming surgeonfish symbionts characterized here and previously described Epulopiscium spp. The broad distribution of endospore formation among the Epulopiscium phylogenetic group raises the possibility that sporulation is a characteristic of the group. We speculate that spore formation in Epulopiscium-like symbionts may be important for dispersal and may also enhance survival in the changing conditions of the fish intestinal tract.

Animals↗

PubMed2004

Initiation of intracellular offspring in Epulopiscium.

Epulopiscium spp. are the largest heterotrophic bacteria yet described. A distinguishing feature of the Epulopiscium group is their viviparous production of multiple, internal offspring as a means of cellular reproduction. Based on their phylogenetic position, among low G + C Gram-positive endospore-forming bacteria, and the remarkable morphological similarity between developing endospores and Epulopiscium offspring, we hypothesized that intracellular offspring production in Epulopiscium evolved from endospore formation. These observations also raise the possibility that a cell with the capacity to form multiple intracellular offspring was the ancestor of all contemporary endospore-forming bacteria. In an effort to characterize mechanisms common to both processes, we describe the earliest stages of offspring formation in Epulopiscium. First, in anticipation of polar division, some of the mother cell DNA coalesces at the cell poles. FtsZ then localizes in a bipolar pattern and the cell divides. A portion of the pole-associated DNA is trapped within the small cells formed by division at both poles. As development progresses, more pole-associated DNA is apparently packaged into the offspring primordia. These results illustrate three mechanisms, the reorganization of cellular DNA, asymmetric division and DNA packaging, that are common to both endospore formation in Bacillus subtilis and the production of active, intracellular offspring in Epulopiscium. Unlike most endospore formers, Epulopiscium partitions only a small proportion of mother cell DNA into the developing offspring.

Animals↗