Mutation rate dynamics reflect ecological change in an emerging zoonotic pathogen

Mutation rates vary both within and between bacterial species, and understanding what drives this variation is essential for understanding the evolutionary dynamics of bacterial populations. In this study, we investigate two factors that are predicted to influence the mutation rate: ecology and genome size. We conducted mutation accumulation experiments on eight strains of the emerging zoonotic pathogen Streptococcus suis. Natural variation within this species allows us to compare tonsil carriage and invasive disease isolates, from both more and less pathogenic populations, with a wide range of genome sizes. We find that invasive disease isolates have repeatedly evolved mutation rates that are higher than those of closely related carriage isolates, regardless of variation in genome size. Independent of this variation in overall rate, we also observe a stronger bias towards G/C to A/T mutations in isolates from more pathogenic populations, whose genomes tend to be smaller and more AT-rich. Our results suggest that ecology is a stronger correlate of mutation rate than genome size over these timescales, and that transitions to invasive disease are consistently accompanied by rapid increases in mutation rate. These results shed light on the impact that ecology can have on the adaptive potential of bacterial pathogens.     

Pseudomonas syringae effector HopZ3 suppresses the bacterial AvrPto1–tomato PTO immune complex via acetylation

The plant pathogen Pseudomonas syringae secretes multiple effectors that modulate plant defenses. Some effectors trigger defenses due to specific recognition by plant immune complexes, whereas others can suppress the resulting immune responses. The HopZ3 effector of P. syringae pv. syringae B728a (PsyB728a) is an acetyltransferase that modifies not only components of plant immune complexes, but also the Psy effectors that activate these complexes. In Arabidopsis, HopZ3 acetylates the host RPM1 complex and the Psy effectors AvrRpm1 and AvrB3. This study focuses on the role of HopZ3 during tomato infection. In Psy-resistant tomato, the main immune complex includes PRF and PTO, a RIPK-family kinase that recognizes the AvrPto effector. HopZ3 acts as a virulence factor on tomato by suppressing AvrPto1_Psy-triggered immunity. HopZ3 acetylates AvrPto1_Psy and the host proteins PTO, SlRIPK and SlRIN4s. Biochemical reconstruction and site-directed mutagenesis experiments suggest that acetylation acts in multiple ways to suppress immune signaling in tomato. First, acetylation disrupts the critical AvrPto1_Psy-PTO interaction needed to initiate the immune response. Unmodified residues at the binding interface of both proteins and at other residues needed for binding are acetylated. Second, acetylation occurs at residues important for AvrPto1_Psy function but not for binding to PTO. Finally, acetylation reduces specific phosphorylations needed for promoting the immune-inducing activity of HopZ3’s targets such as AvrPto1_Psy and PTO. In some cases, acetylation competes with phosphorylation. HopZ3-mediated acetylation suppresses the kinase activity of SlRIPK and the phosphorylation of its SlRIN4 substrate previously implicated in PTO-signaling. Thus, HopZ3 disrupts the functions of multiple immune components and the effectors that trigger them, leading to increased susceptibility to infection. Finally, mass spectrometry used to map specific acetylated residues confirmed HopZ3’s unusual capacity to modify histidine in addition to serine, threonine and lysine residues.     

Suboptimal temperature-dependent changes in the brain development and activity in Galleria mellonella larvae

The development of Galleria mellonella larvae is strongly affected by suboptimal temperature (18°C). One-day-old last-instar larvae react to 18°C with the arrest of further development for several months described as facultative larval diapause. The aim of this study was to find what type of changes, if any, in the brain correlate with the larval diapause induced by suboptimal temperature. Morphological analysis demonstrated the gradual inhibition of brain development. Paraldehyde-fuchsin (PAF) staining revealed cyclicity in the activity of the medial neurosecretory cells (M-NSC) in the larval brain. SDS-PAGE was used to examine the brain proteins of larvae reared at 30°C and at 18°C. The rate of protein synthesis in the brain of the last instar larvae kept at 18°C, measured as l -[³⁵S]methionine incorporation during 2-h incubation in vitro, was only about 40% of the value characteristic for this tissue during normal development (at 30°C). Despite decrease in the rate of total protein synthesis, suboptimal temperature induced an increase in the level of two major brain proteins: 112 and 84 kDa. In SDS-PAGE analysis, these two proteins appear 21–28 days after transfer to the lower temperature. Whether these proteins are specific for induction of larval diapause of Galleria mellonella remains to be further investigated. Arch. Insect Biochem. Physiol. 38:66–73, 1998. © 1998 Wiley-Liss, Inc.     

Molecular characterization of NOS in a mollusc: Expression in a giant modulatory neuron

Here we report on the molecular characterization of the first molluscan NOS in the CNS of the pond snail Lymnaea stagnalis. This Lymnaea NOS (Lym-nNOS) which is expressed preferentially in the CNS is most similar to mammalian neuronal NOS but contains tandem repeats of a seven amino acid motif not found in any other known NOS. We have localized Lym-nNOS to the serotonergic cerebral giant cells (CGCs) which modulate synaptic transmission within a neural network that generates feeding behavior. Our results suggest that the CGCs employ both NO and serotonin in the modulation of the central neural network underlying feeding. © 1998 John Wiley & Sons, Inc. J Neurobiol 35: 65–76, 1998     

Unlocking avian museum collections to enable and advance environmental change research

The rate and magnitude of contemporary changes in natural systems is unprecedented in the Earth's history. Studies of wild birds have been critically important in helping us understand and address these environmental changes. Avian collections provide a potentially unique perspective on change through time, but their role in environmental change research is limited by the availability of collections data. Here we describe how avian collections might be unlocked to enable environmental change research, and discuss the opportunities and constraints associated with this. We use the concept of the extended specimen to describe the types of data that could be unlocked from basic data for discoverability to enhanced data that might be directly applied to environmental change questions. We illustrate the type of environmental change research these data might support. We argue that data creation and access is currently limited by funding for digitization, a rather patchy understanding of the needs of the research community and less than adequate data-sharing by institutions and researchers. We develop a blueprint for addressing these issues which includes (1) improvements in sharing the data we are already creating and (2) building a better case for digitization at scale. As one of the largest avian collections in the world, the Natural History Museum, UK, is committed to unlocking our collections, but we will need input and support from the avian research community to do so.     

Forecasted range shifts of arid-land fishes in response to climate change

Climate change is poised to alter the distributional limits, center, and size of many species. Traits may influence different aspects of range shifts, with trophic generality facilitating shifts at the leading edge, and greater thermal tolerance limiting contractions at the trailing edge. The generality of relationships between traits and range shifts remains ambiguous however, especially for imperiled fishes residing in xeric riverscapes. Our objectives were to quantify contemporary fish distributions in the Lower Colorado River Basin, forecast climate change by 2085 using two general circulation models, and quantify shifts in the limits, center, and size of fish elevational ranges according to fish traits. We examined relationships among traits and range shift metrics either singly using univariate linear modeling or combined with multivariate redundancy analysis. We found that trophic and dispersal traits were associated with shifts at the leading and trailing edges, respectively, although projected range shifts were largely unexplained by traits. As expected, piscivores and omnivores with broader diets shifted upslope most at the leading edge while more specialized invertivores exhibited minimal changes. Fishes that were more mobile shifted upslope most at the trailing edge, defying predictions. No traits explained changes in range center or size. Finally, current preference explained multivariate range shifts, as fishes with faster current preferences exhibited smaller multivariate changes. Although range shifts were largely unexplained by traits, more specialized invertivorous fishes with lower dispersal propensity or greater current preference may require the greatest conservation efforts because of their limited capacity to shift ranges under climate change.     

Macrocyclic inhibitors of Factor XIa: Discovery of alkyl-substituted macrocyclic amide linkers with improved potency

Optimization of macrocyclic inhibitors of FXIa is described which focused on modifications to both the macrocyclic linker and the P1 group. Increases in potency were discovered through interactions with a key hydrophobic region near the S1 prime pocket by substitution of the macrocyclic linker with small alkyl groups. Both the position of substitution and the absolute stereochemistry of the alkyl groups on the macrocyclic linker which led to improved potency varied depending on the ring size of the macrocycle. Replacement of the chlorophenyltetrazole cinnamide P1 in these optimized macrocycles reduced the polar surface area and improved the oral bioavailability for the series, albeit at the cost of a decrease in potency.     

Synthesis,characterization, and cellular localization of a fluorescent probe of the antimalarial 8-aminoquinoline primaquine

Primaquine (PQ) is the only commercially available drug that clears dormant liver stages of malaria and blocks transmission to mosquito vectors. Although an old drug, much remains to be known about the mechanism(s) of action. Herein we develop a fluorescent tagged PQ to discover cellular localization in the human malaria parasite, Plasmodium falciparum. Successful synthesis and characterization of a primaquine-coumarin fluorescent probe (PQCP) demonstrated potency equivalent to the parent drug and the probe was not cytotoxic to HepG2 carcinoma cells. Cellular localization was found primarily in the cytosol of the asexual erythrocytic and gametocyte stages of parasite development.