Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications. We measure the thermoelectric properties of various poly(3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics.

Conjugal opines secreted by crown gall tumours induce strains of Agrobacterium tumefaciens that are donors of Ti plasmids to produce a diffusible conjugation factor. This enhances the conjugal transfer efficiency of the Ti plasmid in other strains of A. tumefaciens. This factor behaves as a secondary messenger, transmitting the environmental information to tra genes. Here we report the use of spectrometry to show that this factor is identical to synthetic N-(beta-oxo-octan-1-oyl)-L-homoserine lactone and confirm that the synthetic compound is biologically active. N-(Hexan-1-oyl)-L-homoserine lactone has also been detected. A closely related molecule, N-(beta-oxo-hexan-1-oyl)-L-homoserine lactone, autoinduces bioluminescence in the distantly related bacterium, Vibrio fischeri. N-Acyl-homoserine lactones thus seem to be conserved molecules in which the length and nature of the lipophilic acyl chain determines the biological function to be regulated. Mutants that do not produce the factor fail to conjugate unless supplied with it in the induction medium (our unpublished data). These data indicate that the conjugation factor is an autoinducer and a key signal molecule in the conjugation system of A. tumefaciens. It is, to our knowledge, the first example of a second messenger molecule in a bacterial conjugation system.

The reduced pressure synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) with sheet-like morphology has been achieved with the introduction of an amphiphilic triblock copolymer into the oxidant thin film. Addition of the copolymer not only results in an oxidant thin film which remains liquid-like under reduced pressure but also induces structured growth during film formation. PEDOT films were polymerized using the vacuum vapor phase polymerization (VPP) technique, in which we show that maintaining a liquid-like state for the oxidant is essential. The resulting conductivity is equivalent to commercially available indium tin oxide (ITO) with concomitant optical transmission values. PEDOT films can be produced with a variety of thicknesses across a range of substrate materials from plastics to metals to ceramics, with sheet resistances down to 45 Ω/□ (ca. 3400 S•cm −1 ), and transparency in the visible spectrum of >80% at 65 nm thickness. This compares favorably to ITO and its currently touted replacements.

Chytridiomycosis is a recently identified fungal disease associated with global population declines of frogs. Although the fungus, Batrachochytrium dendrobatidis, is considered an emerging pathogen, little is known about its population genetics, including the origin of the current epidemic and how this relates to the dispersal ability of the fungus. In this study, we use multilocus sequence typing to examine genetic diversity and relationships among 35 fungal strains from North America, Africa and Australia. Only five variable nucleotide positions were detected among 10 loci (5918 bp). This low level of genetic variation is consistent with the description of B. dendrobatidis as a recently emerged disease agent. Fixed (i.e. 100%) or nearly fixed frequencies of heterozygous genotypes at two loci suggested that B. dendrobatidis is diploid and primarily reproduces clonally. In contrast to the lack of nucleotide polymorphism, electrophoretic karyotyping of multiple strains demonstrated a number of chromosome length polymorphisms.

Biologists have long known that closely related species are often phenotypically different where they occur together, but are indistinguishable where they occur alone. The causes of such character displacement are controversial, however. We used polyphenic spadefoot toad tadpoles (Spea bombifrons and S. multiplicata) to test the hypothesis that character displacement evolves to minimize competition for food. We also sought to evaluate the role of phenotypic plasticity in the mediation of competitive interactions between these species. Depending on their diet, individuals of both species develop into either a small-headed omnivore morph, which feeds mostly on detritus, or a large-headed carnivore morph, which specializes on shrimp. Laboratory experiments and surveys of natural ponds revealed that the two species were more dissimilar in their tendency to produce carnivores when they occurred together than when they occurred alone. This divergence in carnivore production was expressed as both character displacement (where S. multiplicata's propensity to produce carnivores was lower in sympatry than in allopatry) and as phenotypic plasticity (where S. multiplicata facultatively enhanced carnivore production in S. bombifrons, and S. bombifrons facultatively suppressed carnivore production in S. multiplicata). In separate experiments, we established that S. bombifrons (the species for which carnivore production was enhanced) was the superior competitor for shrimp. Conversely, S. multiplicata (the species for which carnivore production was suppressed and omnivore production enhanced) was the superior competitor for detritus. These results therefore demonstrate that selection to minimize competition for food can cause character displacement. They also suggest that both character displacement and phenotypic plasticity may mediate competitive interactions between species.