Long-term survival of haptophyte and prasinophyte resting stages in marine sediment

Resting stages of marine phytoplankton have been shown to have potential for long-term survival and to remain viable in marine sediments for up to about a century. This study documents for the first time long-term survival in haptophytes and prasinophytes, by germination of resting stages of Isochrysis galbana and Mantoniella squamata from up to 40-year-old sediment layers. Germination was induced by setting up sediment slurries in L1 medium at 15°C. Cyst formation was induced in culture strains acquired from the germinations by keeping mixtures of strains in the light or dark at salinities of 20 or 30. The identity of the two species was confirmed by light and electron microscopy as well as LSU and SSU rDNA-based phylogenetic analyses.     

The association of feeding behaviour with the resistance and tolerance to parasites in recently diverged sticklebacks

Divergent natural selection regimes can contribute to adaptive population divergence, but can be sensitive to human‐mediated environmental change. Nutrient loading of aquatic ecosystems, for example, might modify selection pressures by altering the abundance and distribution of resources and the prevalence and infectivity of parasites. Here, we used a mesocosm experiment to test for interactive effects of nutrient loading and parasitism on host condition and feeding ecology. Specifically, we investigated whether the common fish parasite Gyrodactylus sp. differentially affected recently diverged lake and stream ecotypes of three‐spined stickleback (Gasterosteus aculeatus). We found that the stream ecotype had a higher resistance to Gyrodactylus sp. infections than the lake ecotype, and that both ecotypes experienced a cost of parasitism, indicated by negative relationships between parasite load and both stomach fullness and body condition. Overall, our results suggest that in the early stages of adaptive population divergence of hosts, parasites can affect host resistance, body condition and diet.     

Tyrosinase‐catalyzed oxidation of resveratrol produces a highly reactive ortho‐quinone: Implications for melanocyte toxicity

trans‐Resveratrol (3,5,4′‐trihydroxy‐trans‐stilbene, RES), a naturally occurring polyphenol, has recently attracted increased interest as a health‐beneficial agent. However, based on its p‐substituted phenol structure, RES is expected to be a substrate for tyrosinase and to produce a toxic o‐quinone metabolite. The results of this study demonstrate that the oxidation of RES by tyrosinase produces 4‐(3′,5′‐dihydroxy‐trans‐styrenyl)‐1,2‐benzoquinone (RES‐quinone), which decays rapidly to an oligomeric product (RES‐oligomer). RES‐quinone was identified after reduction to its corresponding catechol, known as piceatannol. RES‐quinone reacts with N‐acetylcysteine, a small thiol, to form a diadduct and a triadduct, which were identified by NMR and MS analyses. The production of a triadduct is not common for o‐quinones, suggesting a high reactivity of RES‐quinone. RES‐quinone also binds to bovine serum albumin through its cysteine residue. RES‐oligomer can oxidize GSH to GSSG, indicating its pro‐oxidant activity. These results suggest that RES could be cytotoxic to melanocytes due to the binding of RES‐quinone to thiol proteins.     

Excavating ghost footprints and tangled trees from modern genomes

Due to pervasive gene flow and admixture, simple bifurcating trees often do not provide an accurate representation of relationships among diverging lineages, but limited resolution in the available genomic data and the spatial distribution of samples has hindered detailed insights regarding the evolutionary and demographic history of many species and populations. In this issue of Molecular Ecology, Foote et al. (2019) combine a powerful sampling design with novel analytical methods adopted from human genetics to describe previously unrecognized patterns of recurrent vicariance and admixture among lineages in the globally distributed killer whale (Orcinus orca). Based on sequence data from modern samples alone, they discover clear signatures of ancient admixture with a now extinct “ghost” lineage, providing one of the first accounts of archaic introgression in a nonhominid species. Coupling a cost‐effective sequencing strategy with novel analytical approaches, their paper provides a roadmap for advancing inference of evolutionary history in other nonmodel species, promising exciting times ahead for our field.     

Mosquito control actions affect chironomid diversity in temporary wetlands of the Upper Rhine Valley

The Upper Rhine Valley, a “hotspot of biodiversity” in Germany, has been treated with the biocide Bacillus thuringiensis var. israelensis (Bti) for mosquito control for decades. Previous studies discovered Bti nontarget effects in terms of severe chironomid abundance reductions. In this study, we investigated the impact of Bti on species level and addressed the community composition of the nontarget family Chironomidae by use of community metabarcoding. Chironomid emergence data were collected in three mosquito‐control relevant wetland types in the Upper Rhine Valley. For all three sites the chironomid species composition, based on operational taxonomic units (OTUs), was different to varying degrees in the Bti‐treated samples versus control samples, ranging from a significant 63% OTU reduction to an OTU replacement. We assumed that predatory chironomids are less prone to Bti than filter feeders, as the latter feed on floating particles leading to direct ingestion of Bti. However, a comparable percentage of predators and filter feeders (63% and 65%, respectively) was reduced in the Bti samples, suggesting that the feeding strategy is not the main driver for Bti sensitivity in chironomids. Finally, our data was compared to a three‐year‐old data set, indicating possible chironomid community recovery due to species recolonization a few years after the last Bti application. Considering the currently discussed worldwide insect decline we recommend a rethinking of the usage of the biocide Bti, and to prevent its ongoing application especially in nature protection reserves to enhance ecological resilience and to prevent boosting the current biodiversity loss.     

Streptococcal dTDP‐L‐rhamnose biosynthesis enzymes: functional characterization and lead compound identification

Biosynthesis of the nucleotide sugar precursor dTDP‐L‐rhamnose is critical for the viability and virulence of many human pathogenic bacteria, including Streptococcus pyogenes (Group A Streptococcus; GAS), Streptococcus mutans and Mycobacterium tuberculosis. Streptococcal pathogens require dTDP‐L‐rhamnose for the production of structurally similar rhamnose polysaccharides in their cell wall. Via heterologous expression in S. mutans, we confirmed that GAS RmlB and RmlC are critical for dTDP‐L‐rhamnose biosynthesis through their action as dTDP‐glucose‐4,6‐dehydratase and dTDP‐4‐keto‐6‐deoxyglucose‐3,5‐epimerase enzymes respectively. Complementation with GAS RmlB and RmlC containing specific point mutations corroborated the conservation of previous identified catalytic residues. Bio‐layer interferometry was used to identify and confirm inhibitory lead compounds that bind to GAS dTDP‐rhamnose biosynthesis enzymes RmlB, RmlC and GacA. One of the identified compounds, Ri03, inhibited growth of GAS, other rhamnose‐dependent streptococcal pathogens as well as M. tuberculosis with an IC₅₀ of 120–410 µM. Importantly, we confirmed that Ri03 inhibited dTDP‐L‐rhamnose formation in a concentration‐dependent manner through a biochemical assay with recombinant rhamnose biosynthesis enzymes. We therefore conclude that inhibitors of dTDP‐L‐rhamnose biosynthesis, such as Ri03, affect streptococcal and mycobacterial viability and can serve as lead compounds for the development of a new class of antibiotics that targets dTDP‐rhamnose biosynthesis in pathogenic bacteria.     

Functioning of plant-bacterial associations under osmotic stress in vitro

World Journal of Microbiology and Biotechnology - Derived from RNA, 5?-ribonucleotides, especially Inosine-5?-monophosphate (IMP) and guanosine-5?-monophosphate (GMP), can enhance...     

Arbovirus surveillance using FTATM cards in modified CO2‐baited encephalitis virus surveillance traps in the Northern Territory,Australia

In 2016, modified CO₂‐baited encephalitis virus surveillance (EVS) traps were evaluated for flavivirus surveillance in the Northern Territory, Australia. The traps were fitted with honey‐soaked nucleic acid preservation cards (FTA^TM) for mosquitoes to expectorate virus while feeding on the cards. Cards were tested for the presence of selected arboviruses, with two cards testing positive for Kunjin virus and Alfuy, while sentinel chickens tested in parallel also showed Kunjin virus activity at the same time. The results from the cards and vector mosquito feeding rates indicate that CO₂‐baited EVS traps coupled with honey‐baited FTA^TM cards are an effective tool for broad‐scale arbovirus surveillance.