Aquatic vegetation and largemouth bass population responses to water-level variations in Lake Okeechobee,Florida (USA)

A five-year study examined the responses of submerged aquatic vegetation (SAV), emergent vegetation, and largemouth bass (Micropterus salmoides) to variations in water level in a large lake in Florida, USA. SAV was assessed using a combined transect survey/spatial mapping approach, emergent vegetation was quantified with aerial photography and GIS, and bass were surveyed by electro-shocking. During the period leading up to this study (1995–1999), water levels were high in the lake, and the SAV was reduced in spatial extent and biomass, compared to its condition in the early 1990s. Spatial extent of emergent vegetation also was low, and largemouth bass surveys indicated low densities and failure to recruit young fish into the population. This was attributed to the lack of critical vegetative habitat. In spring 2000, the lake was lowered by discharging water from major outlets, and this was followed by a regional drought. Water levels dropped by 1m, and there was widespread development of Chara lawns in shoreline areas, with coincident increases in water clarity. There was some germination of vascular SAV, but Chara was the extreme dominant, such that structural complexity remained low. There was no substantive improvement in bass recruitment. During 2001, water levels declined further, and emergent plants germinated in exposed areas of the lake bottom. SAV was restricted to sites farther offshore, and continued to be dominated by Chara. There again was no bass response. In 2002, conditions changed when water levels increased to a moderate depth, flooding shoreline habitat to 0.5m. Vascular SAV increased in biomass and spatial extent, such that the community developed a high structural complexity. At the same time, emergent aquatic plants developed dense stands along the western shoreline. Largemouth bass had a strong recruitment of young fish for the first time in 5years. Recruitment continued to be successful in 2003, when spatial extent of SAV was somewhat reduced by higher water but total biomass and diversity remained high. These results demonstrate an important effect of inter-annual variation in water depth on the population dynamics of aquatic plants and fish in a subtropical lake.     

Direct targeting and rapid isolation of BAC clones spanning a defined chromosome region

To isolate genes of interest in plants, it is essential to construct bacterial artificial chromosome (BAC) libraries from specific genotypes. Construction and organisation of BAC libraries is laborious and costly, especially from organisms with large and complex genomes. In the present study, we developed the pooled BAC library strategy that allows rapid and low cost generation and screening of genomic libraries from any genotype of interest. The BAC library is constructed, directly organised into a few pools and screened for BAC clones of interest using PCR and hybridisation steps, without requiring organization into individual clones. As a proof of concept, a pooled BAC library of approximately 177,000 recombinant clones has been constructed from the barley cultivar Cebada Capa that carries the Rph7 leaf rust resistance gene. The library has an average insert size of 140 kb, a coverage of six barley genome equivalents and is organised in 138 pools of about 1,300 clones each. We rapidly established a single contig of six BAC clones spanning 230 kb at the Rph7 locus on chromosome 3HS. The described low-cost cloning strategy is fast and will greatly facilitate direct targeting of genes and large-scale intra- and inter-species comparative genome analysis.Edwige Isidore and Beatrice Scherrer contributed equally to the work.     

Spatial epidemiology and natural population structure of Campylobacter jejuni colonizing a farmland ecosystem

Recent progress in determining the population structure of Campylobacter jejuni, and discerning associations between genotypes and specific niches, has emphasized the shortfall in our understanding of the ecology and epidemiology of this bacterium. We examined the natural structure of the C. jejuni community associated with cattle farmland in the UK by structured spatiotemporal sampling of habitats, including livestock and wild animal faeces, environmental water and soil, over a 10-week period within a 100 km2 area. A total of 172 isolates were characterized using multilocus sequence typing into 65 sequence types (STs). Isolates from cattle faeces were significantly over-represented in the ST-61 complex, whereas isolates from wildlife faeces and water were more likely to belong to the ST-45 complex and a number of unusual STs, many of which were first encountered during this study. Sampling within a narrow spatiotemporal window permitted the application of novel statistical methods exploring the relationship between the genetic relatedness and spatial separation of isolates. This approach showed that isolates from the same sampling squares and squares separated by <1.0 km were genetically more similar than isolates separated by greater distances. Our study demonstrates the potential of multilocus sequence typing combined with spatial modelling in exploring natural transmission pathways for C. jejuni.     

Vascular smooth muscle cells on polyelectrolyte multilayers: hydrophobicity-directed adhesion and growth

Polyelectrolyte multilayer films were employed to support attachment of cultured rat aortic smooth muscle A7r5 cells. Like smooth muscle cells in vivo, cultured A7r5 cells are capable of converting between a nonmotile "contractile" phenotype and a motile "synthetic" phenotype. Polyelectrolyte films were designed to examine the effect of surface charge and hydrophobicity on cell adhesion, morphology, and motility. The hydrophobic nature and surface charge of different polyelectrolyte films significantly affected A7r5 cell attachment and spreading. In general, hydrophobic polyelectrolyte film surfaces, regardless of formal charge, were found to be more cytophilic than hydrophilic surfaces. On the most hydrophobic surfaces, the A7r5 cells adhered, spread, and exhibited little indication of motility, whereas on the most hydrophilic surfaces, the cells adhered poorly if at all and when present on the surface displayed characteristics of being highly motile. The two surfaces that minimized cell adhesion consisted of two varieties of a diblock copolymer containing hydrophilic poly(ethylene oxide) and a copolymer bearing a zwitterionic group AEDAPS, (3-[2-(acrylamido)-ethyldimethyl ammonio] propane sulfonate). Increasing the proportion of AEDAPS in the copolymer decreased the adhesion of cells to the surface. Cells presented with micropatterns of cytophilic and cytophobic surfaces generated by polymer-on-polymer stamping displayed a surface-dependent cytoskeletal organization and a dramatic preference for adhesion to, and spreading on, the cytophilic surface, demonstrating the utility of polyelectrolyte films in manipulating smooth muscle cell adhesion and behavior.     

Non-traditional targets of endocrine disrupting chemicals: the roots of hormone signaling

The topic of endocrine disruption and the broad range of physiologicaleffects caused by endocrine disrupting chemicals (EDCs) canonly be meaningfully framed within an ecological and evolutionarycontext. Environmental pollutants and EDCs operate by disruptingthe "chemical communication" that coordinates signaling withinan organism. Here we discuss how EDCs are also able to disruptthe chemical communication between plants and soil bacterianecessary for initiating nitrogen-fixing symbiosis. We alsoexamine, through examples of pollutant-related impacts on awide range of invertebrates, the need for identifying emergingtargets of EDCs. We suggest broadening the defined field ofendocrine disruption to encompass the effects of synthetic chemicalsthat interfere with signaling and communication, not only withinan organism, but also between organisms and linking ecosystems.The ecological consequences of failing to recognize novel targetsof chemical pollutants and EDCs may be a net loss of biologicaldiversity and a further imbalance of the global nitrogen cycle.     

A new yeast poly(A) polymerase complex involved in RNA quality control

Eukaryotic cells contain several unconventional poly(A) polymerases in addition to the canonical enzymes responsible for the synthesis of poly(A) tails of nuclear messenger RNA precursors. The yeast protein Trf4p has been implicated in a quality control pathway that leads to the polyadenylation and subsequent exosome-mediated degradation of hypomethylated initiator tRNA^Met (tRNA_i^Met). Here we show that Trf4p is the catalytic subunit of a new poly(A) polymerase complex that contains Air1p or Air2p as potential RNA-binding subunits, as well as the putative RNA helicase Mtr4p. Comparison of native tRNA_i^Met with its in vitro transcribed unmodified counterpart revealed that the unmodified RNA was preferentially polyadenylated by affinity-purified Trf4 complex from yeast, as well as by complexes reconstituted from recombinant components. These results and additional experiments with other tRNA substrates suggested that the Trf4 complex can discriminate between native tRNAs and molecules that are incorrectly folded. Moreover, the polyadenylation activity of the Trf4 complex stimulated the degradation of unmodified tRNA_i^Met by nuclear exosome fractions in vitro. Degradation was most efficient when coupled to the polyadenylation activity of the Trf4 complex, indicating that the poly(A) tails serve as signals for the recruitment of the exosome. This polyadenylation-mediated RNA surveillance resembles the role of polyadenylation in bacterial RNA turnover.     

Locally Addressable Electrochemical Patterning Technique (LAEPT) applied to poly(L-lysine)-graft-poly(ethylene glycol) adlayers on titanium and silicon oxide surfaces

The protein-resistant polycationic graft polymer, poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), was uniformly adsorbed onto a homogenous titanium surface and subsequently subjected to a direct current (dc) voltage. Under the influence of an ascending cathodic and anodic potential, there was a steady and gradual loss of PLL-g-PEG from the conductive titanium surface while no desorption was observed on the insulating silicon oxide substrates. We have implemented this difference in the electrochemical response of PLL-g-PEG on conductive titanium and insulating silicon oxide regions as a biosensing platform for the controlled surface functionalization of the titanium areas while maintaining a protein-resistant background on the silicon oxide regions. A silicon-based substrate was micropatterned into alternating stripes of conductive titanium and insulating silicon oxide with subsequent PLL-g-PEG adsorption onto its surfaces. The surface modified substrate was then subjected to +1800 mV (referenced to the silver electrode). It was observed that the potentiostatic action removed the PLL-g-PEG from the titanium stripes without inducing any polyelectrolyte loss from the silicon oxide regions. Time-of-flight secondary ions mass spectroscopy and fluorescence microscopy qualitatively confirmed the PLL-g-PEG retention on the silicon oxide stripes and its absence on the titanium region. This method, known as "Locally Addressable Electrochemical Patterning Technique" (LAEPT), offers great prospects for biomedical and biosensing applications. In an attempt to elucidate the desorption mechanism of PLL-g-PEG in the presence of an electric field on titanium surface, we have conducted electrochemical impedance spectroscopy experiments on bare titanium substrates. The results showed that electrochemical transformations occurred within the titanium oxide layer; its impedance and polarization resistance were found to decrease steadily upon both cathodic and anodic polarization resulting in the polyelectrolyte desorption from the titanium surface.