Interplay between Yersinia pestis and its flea vector in lipoate metabolism

To thrive, vector-borne pathogens must survive in the vector’s gut. How these pathogens successfully exploit this environment in time and space has not been extensively characterized. Using Yersinia pestis (the plague bacillus) and its flea vector, we developed a bioluminescence-based approach and employed it to investigate the mechanisms of pathogenesis at an unprecedented level of detail. Remarkably, lipoylation of metabolic enzymes, via the biosynthesis and salvage of lipoate, increases the Y. pestis transmission rate by fleas. Interestingly, the salvage pathway’s lipoate/octanoate ligase LplA enhances the first step in lipoate biosynthesis during foregut colonization but not during midgut colonization. Lastly, Y. pestis primarily uses lipoate provided by digestive proteolysis (presumably as lipoyl peptides) rather than free lipoate in blood, which is quickly depleted by the vector. Thus, spatial and temporal factors dictate the bacterium’s lipoylation strategies during an infection, and replenishment of lipoate by digestive proteolysis in the vector might constitute an Achilles’ heel that is exploited by pathogens.Subject terms: Bacterial pathogenesis, Metabolism     

Temperature and host diet jointly influence the outcome of infection in a Daphnia-fungal parasite system

1. Climate change has the potential to shape the future of infectious diseases, both directly and indirectly. In aquatic systems, for example, elevated temperatures can modulate the infectivity of waterborne parasites and affect the immune response of zooplanktonic hosts. Moreover, lake warming causes shifts in the communities of primary producers towards cyanobacterial dominance, thus lowering the quality of zooplankton diet. This may further affect host fitness, resulting in suboptimal resources available for parasite growth.
2. Previous experimental studies have demonstrated the respective effects of temperature and host diet on infection outcomes, using the zooplankter Daphnia and its microparasites as model systems. Although cyanobacteria blooms and heat waves are concurrent events in nature, few attempts have been made to combine both stressors in experimental settings.
3. Here, we raised the zooplankter Daphnia (two genotypes) under a full factorial design with varying levels of temperature (the standard 19°C and elevated 23°C), food quality (Scenedesmus obliquus as high-quality green algae, Microcystis aeruginosa and Planktothrix agardhii as low-quality cyanobacteria) and exposed them to the parasitic yeast Metschnikowia bicuspidata. We recorded life history parameters of the host as well as parasite traits related to transmission.
4. The combination of low-quality cyanobacterial diets and elevated temperature resulted in additive detrimental effects on host fecundity. Low-quality diets reduced parasite output, while temperature effects were context dependent. Overall, we argue that the combined effects of elevated water temperature and poor-quality diets may decrease epidemics of a common fungal parasite under a climate change scenario.

     

Morphological complexity affects the diversity of marine microbiomes

Large eukaryotes support diverse communities of microbes on their surface—epibiota—that profoundly influence their biology. Alternate factors known to structure complex patterns of microbial diversity—host evolutionary history and ecology, environmental conditions and stochasticity—do not act independently and it is challenging to disentangle their relative effects. Here, we surveyed the epibiota from 38 sympatric seaweed species that span diverse clades and have convergent morphology, which strongly influences seaweed ecology. Host identity explains most of the variation in epibiont communities and deeper host phylogenetic relationships (e.g., genus level) explain a small but significant portion of epibiont community variation. Strikingly, epibiota community composition is significantly influenced by host morphology and epibiota richness increases with morphological complexity of the seaweed host. This effect is robust after controlling for phylogenetic non-independence and is strongest for crustose seaweeds. We experimentally validated the effect of host morphology by quantifying bacterial community assembly on latex sheets cut to resemble three seaweed morphologies. The patterns match those observed in our field survey. Thus, biodiversity increases with habitat complexity in host-associated microbial communities, mirroring patterns observed in animal communities. We suggest that host morphology and structural complexity are underexplored mechanisms structuring microbial communities.Subject terms: Microbial ecology, Biodiversity     

Genomic analysis of multiple Roseophage SIO1 strains

Roseophage SIO1 is a lytic marine phage that infects Roseobacter SIO67, a member of the Roseobacter clade of near-shore alphaproteobacteria. Roseophage SIO1 was first isolated in 1989 and sequenced in 2000. We have re-sequenced and re-annotated the original isolate. Our current annotation could only assign functions to seven additional open reading frames, indicating that, despite the advances in bioinformatics tools and increased genomic resources, we are still far from being able to translate phage genomic sequences into biological functions. In 2001, we isolated four new strains of Roseophage SIO1 from California near-shore locations. The genomes of all four were sequenced and compared against the original Roseophage SIO1 isolated in 1989. A high degree of conservation was evident across all five genomes; comparisons at the nucleotide level yielded an average 97% identity. The observed differences were clustered in protein-encoding regions and were mostly synonymous. The one strain that was found to possess an expanded host range also showed notable changes in putative tail protein-coding regions. Despite the possibly rapid evolution of phage and the mostly uncharacterized diversity found in viral metagenomic data sets, these findings indicate that viral genomes such as the genome of SIO1-like Roseophages can be stably maintained over ecologically significant time and distance (i.e. over a decade and ∼50 km).