The effects of morpholine pre-treated and carboxymethylated cellulose nanofibrils on the properties of alginate-based hydrogels.

The effects of varying percentage loadings of morpholine pre-treated cellulose nanofibrils (MCNF) and carboxymethylated cellulose nanofibrils (CMCNF) on the aqueous swelling, compressive modulus and viscoelastic properties of calcium-ion-crosslinked alginate hydrogels were investigated. In addition, the pore structures of hydrogels with the highest compressive modulus were studied. The incorporation of 5 wt. % MCNF resulted in a slightly reduced aqueous swelling, a 36% increase in compressive modulus and a layered pore structure when compared with the neat alginate hydrogel. On the other hand, the addition of CMCNF at the same loading led to a slightly improved aqueous swelling, an increase in compressive modulus (17%) and high porosity. Further increases in CNF loadings did not result in significant increase in material properties. The alginate/CNF composite materials have potentials to be used in applications where good swelling and mechanical robustness are required.

Direct estimation of per nucleotide and genomic deleterious mutation rates in Drosophila.

Spontaneous mutations are the source of genetic variation required for evolutionary change, and are therefore important for many aspects of evolutionary biology. For example, the divergence between taxa at neutrally evolving sites in the genome is proportional to the per nucleotide mutation rate, u (ref. 1), and this can be used to date speciation events by assuming a molecular clock. The overall rate of occurrence of deleterious mutations in the genome each generation (U) appears in theories of nucleotide divergence and polymorphism, the evolution of sex and recombination, and the evolutionary consequences of inbreeding. However, estimates of U based on changes in allozymes or DNA sequences and fitness traits are discordant. Here we directly estimate u in Drosophila melanogaster by scanning 20 million bases of DNA from three sets of mutation accumulation lines by using denaturing high-performance liquid chromatography. From 37 mutation events that we detected, we obtained a mean estimate for u of 8.4 x 10(-9) per generation. Moreover, we detected significant heterogeneity in u among the three mutation-accumulation-line genotypes. By multiplying u by an estimate of the fraction of mutations that are deleterious in natural populations of Drosophila, we estimate that U is 1.2 per diploid genome. This high rate suggests that selection against deleterious mutations may have a key role in explaining patterns of genetic variation in the genome, and help to maintain recombination and sexual reproduction.

Molecular phylogenetic analysis of the genus Strongyloides and related nematodes.

Strongyloides spp., parasitic nematodes of humans and many other terrestrial vertebrates, display an unusual heterogonic lifecycle involving alternating parasitic and free-living adult reproductive stages. A number of other genera have similar lifecycles, but their relationships to Strongyloides have not been clarified. We have inferred a phylogeny of 12 species of Strongyloides, Parastrongyloides, Rhabdias and Rhabditophanes using small subunit ribosomal RNA gene (SSU rDNA) sequences. The lineage leading to Strongyloides appears to have arisen within parasites of terrestrial invertebrates. Inferred lifecycle evolution was particularly dynamic within these nematodes. Importantly, the free-living Rhabditophanes sp. KR3021 is placed within a clade of parasitic taxa, suggesting that this species may represent a reversion to a non-parasitic lifecycle. Species within the genus Strongyloides are very closely related, despite the disparity of host species parasitised. The highly pathogenic human parasite Strongyloides fuelleborni kelleyi is not supported as a subspecies of the primate parasite S. fuelleborni fuelleborni, but is most likely derived from a local zoonotic source.