Effects of bacterial physiological states and bacterial species on host–microbe interactions

Abstract

This study investigated how the physiological states of Aggregatibacter actinomycetemcomitans (Aa) and Streptococcus mitis affect their intracellular invasion capabilities and the resulting host cell responses. The physiological states included two forms of planktonic states, floating or sedimented (by centrifugation) and the biofilm state (with centrifugation). Confluent epithelial Ca9-22 cells were challenged with floating or sedimented planktonic cultures, or with 24-h biofilms for 3?h. The results show that intracellular invasion efficiencies were clearly affected by the bacterial physiological states. For both bacterial species, the sedimented-cells displayed 2–10 times higher invasion efficiency than the floating-cells (p?<?0.05). The invasion efficiency of Aa biofilms was three fold lower than sedimented cells, whereas those of S. mitis biofilms were similar to sedimented cells. Unlike invasion, the metabolic activities of Ca9-22 were unaffected by different bacterial physiological states. However, Aa biofilms induced higher IL-1β expression than planktonic cultures. In conclusion, different bacterial physiological states can affect the outcomes of (in vitro) host–microbe interaction in different ways.     

Coevolution of resource trade-offs driving species interactions in a host–parasite network: an exploratory model

Patterns of specialization asymmetry, where specialist species interact mainly with generalists while generalists interact with both generalists and specialists, are often observed in mutualistic and antagonistic bipartite ecological networks. These have been explained in terms of the relative abundance of species, using a null model that assigns links in proportion to abundance, but doubts have been raised as to whether this offers a complete explanation. In particular, host–parasite networks offer a variety of examples in which the reverse patterns are observed. We propose that the link between specificity and species richness may also be driven by the coevolution of hosts and parasites, as hosts allocate resources to optimize defense against parasites, and parasites to optimize attack on hosts. In this hypothesis, species interactions are a result of resource allocations. This novel concept, linking together many different arguments for network structures, is introduced through the adaptive dynamics of a simple ecological toy system of two hosts and two parasites. We analyze the toy model and its functionality, demonstrating that coevolution leads to specialization asymmetry in networks with closely related parasites or fast host mutation rates, but not in networks with more distantly related species. Having constructed the toy model and tested its applicability, our model can now be expanded to the full problem of a larger system.     

Life history interactions with environmental conditions in a host–parasite relationship and the parasite's mode of transmission

The microsporidian parasite Edhazardia aedis is capable of vertical or horizontal transmission among individuals of its host, the mosquito Aedes aegypti, and either mode of transmission may follow the other. We show that following the horizontal infection of host larvae, the parasite's subsequent mode of transmission largely depends on host life history traits and their responses to different environmental conditions. In two experiments the intensity of larval exposure to infection and the amount of food available to them were simultaneously manipulated. One experiment followed the dynamics of host development and the parasite's production of spores while the other estimated the outcome of their relationship. Host life history traits varied widely across treatment conditions while those of the parasite did not. Of particular importance was the host's larval growth rate. Horizontal rather than vertical transmission by the parasite was more likely as low food and high dose conditions favoured slower larval growth rates. This pattern of transmission behaviour with host growth rate can be considered in terms of reproductive value: the potential vertical transmission success that female mosquitoes offer the parasite decreases as larval growth rates slow and makes them more attractive to exploitation for horizontal transmission (requiring host mortality). However, the lack of variation in the parasite's life history traits gave rise in some conditions to low estimates for both its vertical and horizontal transmission success. We suggest that the unresponsive behaviour of the parasite's life history traits reflects a bet-hedging strategy to reduce variance in its overall transmission success in the unpredictable environmental conditions and host larval growth rates that this parasite encounters in nature.     

Host–parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird

Egg mimicry by obligate avian brood parasites and host rejection of non-mimetic eggs are well-known textbook examples of host-parasite coevolution. By contrast, reciprocal adaptations and counteradaptations beyond the egg stage in brood parasites and their hosts have received less attention. The screaming cowbird (Molothrus rufoaxillaris) is a specialist obligate brood parasite whose fledglings look identical to those of its primary host, the baywing (Agelaioides badius). Such a resemblance has been proposed as an adaptation in response to host discrimination against odd-looking young, but evidence supporting this idea is scarce. Here, we examined this hypothesis by comparing the survival rates of young screaming cowbirds and non-mimetic shiny cowbirds (Molothrus bonariensis) cross-fostered to baywing nests and quantifying the similarity in plumage colour and begging calls between host and cowbird fledglings. Shiny cowbirds suffered higher post-fledging mortality rates (83%) than screaming cowbirds (0%) owing to host rejection. Visual modelling revealed that screaming cowbirds, but not shiny cowbirds, were indistinguishable from host young in plumage colour. Similarly, screaming cowbirds matched baywings' begging calls more closely than shiny cowbirds. Our results strongly support the occurrence of host fledgling mimicry in screaming cowbirds and suggest a role of visual and vocal cues in fledgling discrimination by baywings.     

Temporal variations of Microsporidia diversity and discovery of new host–parasite interactions in a lake ecosystem

Microsporidia are a large group of obligate intracellular eukaryotic parasites related to Fungi. Recent studies suggest that their diversity has been greatly underestimated and little is known about their hosts other than metazoans, and thus about their impact on the communities at the base of the food web. In this work, we therefore studied the diversity of Microsporidia over one year and identified potential new hosts in small-sized fractions (<150 μm) in a lake ecosystem using a metabarcoding approach coupled with co-occurrence networks and tyramide signal amplification-fluorescent in situ hybridization. Our analysis shows a great Microsporidia diversity (1 472 OTUs), with an important part of this diversity being unknown. Temporal variations of this diversity have been observed, which might follow temporal variations of their potential hosts such as protists and microzooplankton. New hosts among them were identified as well as associations with phytoplankton. Indeed, repeated infections were observed in Kellicottia (rotifers) with a prevalence of 38% (infected individuals). Microsporidia inside a Stentor (ciliate) were also observed. Finally, potential infections of the diatom Asterionella were identified (prevalence <0.1%). The microsporidian host spectrum could be therefore even more important than previously described, and their role in the functioning of lake ecosystems is undoubtedly largely unknown.     

Length–weight relationships of six marine fish species from the coast of Ghana

This study estimated the LWRs of six fishes from the coastal waters of Greater Accra, Ghana. Data was obtained monthly from June 2018 to July 2019 and analyzed for total length and weight measurement to the nearest 0.1 cm and 0.01 g respectively. The sampling was done using hooks and line as well as monofilament and multifilament gear types. The mesh sizes for both monofilament and multifilament gear types ranged from 0.5 to 2 inches whereas the hooks types ranged from 6 to 12. The b values for the assessed species were within the range 2.8–3.2. There was strong correlation between the length and weight of all the species (R² > .95). This study provides LWRs for Cynoglossus senegalensis, Scorpaena histrio and Pseudotolithus senegalensis and larger maximum total length (TLmax) for Syacium micrurum, Eucinostomus melanopterus and Brachydeuterus auritus.     

Arabidopsis thaliana and the Robin Hood parasite: a chivalrous oomycete that steals fitness from fecund hosts and benefits the poorest one?

Are parasites always harmful to their hosts? By definition, indeed, but in a few cases and particular environments, hosts experience higher fitness in the presence than in the absence of their parasites. Symbiotic associations form a continuum of interactions, from deleterious to beneficial effects on hosts. In this paper, we investigate the outcome of parasite infection of Arabidopsis thaliana by its natural pathogen Hyaloperonospora arabidopsis. This system exhibits a wide range of parasite impact on host fitness with, surprisingly, deleterious effects on high fecundity hosts and, at the opposite extreme, seemingly beneficial effects on the least fecund one. This phenomenon might result from varying levels of tolerance among host lines and even overcompensation for parasite damage analogous to what can be observed in plant–herbivore systems.     

Interactions between environmental stressors: the influence of salinity on host–parasite interactions between Daphnia magna and Pasteuria ramosa

Interactions between environmental stressors play an important role in shaping the health of an organism. This is particularly true in terms of the prevalence and severity of infectious disease, as stressors in combination will not always act to simply decrease the immune function of a host, but may instead interact to compound or even oppose the influence of parasitism on the health of an organism. Here, we explore the impact of environmental stress on host–parasite interactions using the water flea Daphnia magna and it is obligate parasite Pasteuria ramosa. Utilising an ecologically relevant stressor, we focus on the combined effect of salinity and P. ramosa on the fecundity and survival of the host, as well as on patterns of infectivity and the proliferation of the parasite. We show that in the absence of the parasite, host fecundity and survival was highest in the low salinity treatments. Once a parasite was introduced into the environment, however, salinity and parasitism acted antagonistically to influence both host survival and fecundity, and these patterns of disease were unrelated to infection rates or parasite spore loads. By summarising the form of interactions found in the broader Daphnia literature, we highlight how the combined effect of stress and parasitism will vary with the type of stressor, the trait used to describe the health of Daphnia and the host–parasite combination under observation. Our results highlight how the context-dependent nature of interactions between stress and parasitism inevitably complicates the link between environmental factors and the prevalence and severity of disease.     

Introduction of Alien Host–parasite Complexes in a Natural Environment and the Symbiota Concept

When a species is introduced in a new territory its parasites may also follow, thus forming a sort of biotic unit. We propose the term symbiota to indicate this host–parasite complex. This concept is at the basis of the present research in which 11 species of alien and native freshwater fish were collected by electrofishing in the Po river area (Northern Italy). The alien host fish Ictalurus melas and Silurus glanis were parasitized by only one monogenean species each. Lepomis gibbosus, of North American origin, hosted four monogeneans and Carassius carassius three. All these parasites should be considered as alien species, except those collected from C. carassius that should be considered in part natives and in part aliens.     

The scales of the zebrafish: host–microbiota interactions from proteins to populations

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Length–weight and length-length relationship of eight marine fish species from Northeastern Brazilian coast

Length-weight relationships (LWR) and length-length relationships (LLR) were provided for eight species inhabiting Northeastern Brazilian coast. Nine transects (5, 15, 30 m deep) between Sergipe and Vaza-Barris rivers mouths were sampled monthly from September 2013 to August 2014. Each sampling was carried out using a shrimp boat equipped with double ring nets (4 m mouth wide, 10 m long and 20 mm mesh size) and trawlings were performed for 15 min. Fishes were measured (standard and total length, 0.1 cm) and weighted (total weight, 0.01 g). We provide LWR and LLR coefficients for these eight species, including new maximum TL for five species, and discuss the similarity of these results with estimates available in Fishbase.     

Variation and covariation in infectivity,virulence and immunodepression in the host–parasite association Gammarus pulex–Pomphorhynchus laevis

Parasites often manipulate host immunity for their own benefit, either by exacerbating or suppressing the immune response and this may directly affect the expression of parasite virulence. However, genetic variation in immunodepression, which is a prerequisite to its evolution, and the relationship between immunodepression and virulence, have rarely been studied. Here, we investigated the variation among sibships of the acanthocephalan parasite, Pomphorhynchus laevis, in infecting and in immunodepressing its amphipod host, Gammarus pulex. We also assessed the covariation between infectivity, parasite-induced immune depression and host mortality (parasite virulence). We found that infectivity, the intensity of immunodepression and virulence were variable among parasite sibships. Infectivity and the level of immunodepression were not correlated across parasite sibships. Whereas infectivity was unrelated to host mortality, we found that gammarids that were exposed to the parasite sibships that immunodepressed their hosts the most survived better. This positive covariation between host survival and immunodepression suggests that gammarids exposed to the less immunodepressive parasites could suffer from damage imposed by a higher activity of the phenoloxidase.     

Host specificity and genealogy of the louse Polyplax serrata on field mice, Apodemus species: a case of parasite duplication or colonisation?

The genealogy, population structure and population dynamics of the sucking louse Polyplax serrata were analysed across four host species of the genus Apodemus. An analysis of 126 sequences of cytochrome c oxidase subunit I using phylogenetic approaches and haplotype networking revealed a clear structure of European samples, forming three distinct and genetically distant clades with different host specificities. Although a clear connection was detected between the host and parasite genealogies/phylogenies, a uniform pattern of co-speciation was not found. For example, a dramatic shift in the degree of host specificity was demonstrated for two related louse lineages living in sympatry and sharing one of their host species. While one of the louse lineages frequently parasitised two different host taxa (Apodemus sylvaticus and Apodemus flavicollis), the other louse lineage was strictly specific to A. flavicollis. The estimate of divergence time between the two louse lineages indicates that they may have arisen due to parasite duplication on A. flavicollis.     

Yellow fever and dengue—the interactions of virus,vector and host in the re-emergence of epidemic disease

The incidence of the mosquito-borne flavivirus diseases, yellow fever, dengue and dengue hemorrhagic fever has increased dramatically in recent years. Both diseases are characterized by the emergence of explosive epidemics. Yellow fever outbreaks appear to have a periodicity dependent upon fluctuations in sylvatic (enzootic) transmission cycles and the ecological factors that influence these cycles. Spread of the virus from the sylvatic cycle to human settlements, ultimately with interhuman transmission by domestic Aedes aegypti is a repeating event in Africa, and presents a renewed threat in the Americas, where effective Ae. aegypti control collapsed in the 1970s. The incidence of dengue has also increased dramatically in recent years, with up to 80 million persons living in tropical regions of the world now affected annually—an attack rate of 4%. The severe form, dengue hemorrhagic fever (DHF) has become a leading health problem throughout Asia in the last 20 years and is emerging as an epidemic disease in the Americas. Unlike yellow fever, sylvatic dengue transmission cycles are not responsible for disease emergence. The major factors underlying dengue epidemics are changes in human ecology, increasing contact with Ae. aegypti, the co-circulation of multiple dengue serotypes, and a rising prevalence of immunity and immunopathological events that underlie the pathogenesis of DHF. In this review, the complex interplay of virus, host, vector, environment and weather in the ecology of yellow fever and dengue are explored.