A Role for Amyloid in Cell Aggregation and Biofilm Formation

Cell adhesion molecules in Saccharomyces cerevisiae and Candida albicans contain amyloid-forming sequences that are highly conserved. We have now used site-specific mutagenesis and specific peptide perturbants to explore amyloid-dependent activity in the Candida albicans adhesin Als5p. A V326N substitution in the amyloid-forming region conserved secondary structure and ligand binding, but abrogated formation of amyloid fibrils in soluble Als5p and reduced cell surface thioflavin T fluorescence. When displayed on the cell surface, Als5p with this substitution prevented formation of adhesion nanodomains and formation of large cellular aggregates and model biofilms. In addition, amyloid nanodomains were regulated by exogenous peptides. An amyloid-forming homologous peptide rescued aggregation and biofilm activity of Als5pV326N cells, and V326N substitution peptide inhibited aggregation and biofilm activity in Als5pWT cells. Therefore, specific site mutation, inhibition by anti-amyloid peturbants, and sequence-specificity of pro-amyloid and anti-amyloid peptides showed that amyloid formation is essential for nanodomain formation and activation

Low-productivity boreal forests have high conservation value for lichens

1. Land set aside for preservation of biodiversity often has low productivity. As biodiversity generally increases with productivity, due to higher or more diverse availability of resources, this implies that some of the biodiversity may be left unprotected. Due to a lack of knowledge on the species diversity and conservation value of low-productivity habitats, the consequences of the biased allocation of low-productivity land for set-asides are unknown. 2. We examined the conservation value of boreal low-productivity forests (potential tree growth <1 m(3) ha(-1) year(-1)) by comparing assemblages of tree- and deadwood-dwelling lichens and forest stand structure between productive and low-productivity forest stands. We surveyed 84 Scots pine-dominated stands in three regions in Sweden, each including four stand types: two productive (managed and unman-aged) and two low-productivity stands (on mires and on thin, rocky soils). 3. Lichen species richness was the highest in low-productivity stands on thin soil, which had similar amounts and diversity of resources (living trees and dead wood) to productive unmanaged stands. Stands in low-productivity mires, which had low abundance of living trees and dead wood, hosted the lowest lichen richness. Lichen species composition differed among stand types, but none of them hosted unique species. The differences in both species richness and composition were more pronounced in northern than in southern Sweden, likely due to shorter history of intensive forestry. 4. Synthesis and applications. Boreal low-productivity forests can have as high conservation value as productive forests, which should be reflected in conservation strategies. However, their value is far from uniform, and conservation planning should acknowledge this variation and not treat all low-productivity forests as a uniform group. Some types of low-productivity forest (e.g. on rocky soil) are more valuable than others (e.g. on mires), and should thus be prioritized in conservation. It is also important to consider the landscape context: low-productivity forests may have higher value in landscapes where high-productivity forests are highly influenced by forestry. Finally, although low-productivity forests can be valuable for some taxa, productive forests may still be important for other taxa

Plant genotype influences aquatic-terrestrial ecosystem linkages through timing and composition of insect emergence

Terrestrial leaf litter provides aquatic insects with an energy source and habitat structure,and species differences in litter can influence aquatic insect emergence. Emerging insects also provide energy to riparian predators. We hypothesized that plant genetics would influence the composition and timing of emerging insect communities among individual genotypes of Populus angustifolia varying in litter traits. We also compared the composition and timing of emerging insect communities on litter from mixed genotypes of three cross types of a hybridizing cottonwood complex: P. angustifolia, P. fremontii, and their F1 hybrids. Using litter harvested from an experimental common garden, we measured emerging insect community composition, abundance, and production for 12 weeks in large litter packs affixed with emergence traps. Five major findings emerged. (1) In support of the genetic similarity hypothesis, we found that, among P. angustifolia tree genotypes, litter from more closely related genotypes had more similar litter thickness, nitrogen concentrations, decomposition rates, and emerging insect communities. (2) Genetic similarity was not correlated with other litter traits, although the litter fungal community was a strong predictor of emerging insect communities. (3) Litter decomposition rate, which was the strongest predictor of emerging aquatic insect communities, was influenced by litter thickness, litter N, and the litter fungal community. (4) In contrast to strong community composition differences among P. angustifolia genotypes, differences in community composition between P. fremontii and P. angustifolia were only marginally significant, and communities on F1 hybrids were indistinguishable from P. angustifolia despite genetic and litter trait differences. (5) Mixed litter packs muted the genetic effects observed in litter packs con- sisting of single genotypes. These results demonstrate that the genetic structure of riparian forests can affect the composition and timing of aquatic insect emergence. Because many riparian trees are clonal, including P. angustifolia, large clone size is likely to result in patches of genetically structured leaf litter that may influence the timing and composition of insect emergence within watersheds. Riparian restoration efforts incorporating different tree genotypes could also influence the biodiversity of emerging aquatic insects. Our work illustrates the importance of plant genes for community and ecosystem processes in riparian corridors

Species trait selection along a prescribed fire chronosequence

1. Fire is a widespread management practice used in the maintenance of European heathland. Frequent prescribed burns in small patches have been shown to benefit carabid communities; however, how fire favours specific life-history traits is poorly understood. 2. In this study, we identify characteristic species of the successional stages within heathlands, and find the traits which are characteristic of species in burnt areas versus areas dominated by older heath stands. 3. We identify 10 species as indicator species for heathland in the pioneer stage (0–5 years old); Amara lunicollis, Bembidion lampros, Calathus fuscipes, Carabus problematicus, Cicindela campestris, Nebria salina, Notiophilus aquaticus, Poecilus cupreus, P. lepidus and P. versicolor. Dyschirius globosus is identified as an indicator for the building stage (6–14 years old), and Carabus violaceus as an indicator for the mature stage (15–25 years old). 4. Moisture preference and diet are identified as traits that determine species response to prescribed fire. Collembolan specialists and species with no moisture preference are shown to be most abundant in burnt patches, whereas generalist predators and species with a high moisture preference are less tolerant of fire. 5. Knowledge of species sorting along a prescribed fire gradient can provide valuable information for heathland conservation.publishedVersio

A Landscapeâ Based Classification of Fish Assemblages in Sampled and Unsampled Lakes

We related fish species patterns and landscapeâ scale environmental data from 216 Michigan lakes to identify repeatable types of fish assemblages, identify environmental factors related to assemblage types, and classify fish assemblages in unsampled lakes. Multivariate regression tree modeling of fish species abundances identified six assemblage types that were explained by degreeâ days during the iceâ free period, lake surface area, and mean lake surface temperature. Warmwater species dominated southern lakes, while coolwater and coldwater species had higher abundances in northern lakes. Coolwater species were present in large southern lakes, whereas warmwater species were excluded from northern lakes that had low mean surface temperatures or low degreeâ days. These results suggest that patterns of lake fish assemblages are shaped by differences in climate as well as lakeâ specific differences in surface temperature regimes and in vertical availability of coldwater and coolwater habitats. Because we related fish patterns to readily available landscapeâ level data, our approach can be used to characterize fish assemblages in all lakes across broad geographic extents.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142256/1/tafs0414.pd

Force Sensitivity in Saccharomyces cerevisiae Flocculins

Many fungal adhesins have short, -aggregation-prone sequences that play important functional roles, and in the Candida albicans adhesin Als5p, these sequences cluster the adhesins after exposure to shear force. Here, we report that Saccharomyces cerevisiae flocculins Flo11p and Flo1p have similar -aggregation-prone sequences and are similarly stimulated by shear force, despite being nonhomologous. Shear from vortex mixing induced the formation of small flocs in cells expressing either adhesin. After the addition of Ca2, yeast cells from vortex-sheared populations showed greatly enhanced flocculation and displayed more pronounced thioflavin-bright surface nanodomains. At high concentrations, amyloidophilic dyes inhibited Flo1p- and Flo11p-mediated agar invasion and the shear-induced increase in flocculation. Consistent with these results, atomic force microscopy of Flo11p showed successive force-distance peaks characteristic of sequentially unfolding tandem repeat domains, like Flo1p and Als5p. Flo11p-expressing cells bound together through homophilic interactions with adhesion forces of up to 700 pN and rupture lengths of up to 600 nm. These results are consistent with the potentiation of yeast flocculation by shear-induced formation of high-avidity domains of clustered adhesins at the cell surface, similar to the activation of Candida albicans adhesin Als5p. Thus, yeast adhesins from three independent gene families use similar force dependent interactions to drive cell adhesion

Imaging the nanoscale organization of peptidoglycan in living Lactococcus lactis cells

Peptidoglycans provide bacterial cell walls with mechanical strength. The spatial organization of peptidoglycan has previously been difficult to study. Here, atomic force microscopy, together with cells carrying mutations in cell-wall polysaccharides, has allowed an in-depth study of these molecules