Subpoblaciones quimiotípicas en cianobacterias planctónicas. Ecología y aplicación en herramientas avanzadas de monitorización

Tesis doctoral inédita, leída en Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología. Fecha de lectura: 08-11-201

Adaptation of a chytrid parasite to Its cyanobacterial host Is hampered by host intraspecific diversity

Experimental evolution can be used to test for and characterize parasite and pathogen adaptation. We undertook a serial-passage experiment in which a single parasite population of the obligate fungal (chytrid) parasite Rhizophydium megarrhizum was maintained over a period of 200 days under different mono- and multiclonal compositions of its phytoplankton host, the bloom-forming cyanobacterium Planktothrix. Despite initially inferior performance, parasite populations under sustained exposure to novel monoclonal hosts experienced rapid fitness increases evidenced by increased transmission rates. This demonstrates rapid adaptation of chytrids to novel hosts and highlights their high evolutionary potential. In contrast, increased fitness was not detected in parasites exposed to multiclonal host mixtures, indicating that cyanobacterial intraspecific diversity hampers parasites adaptation. Significant increases in intensity of infection were observed in monoclonal and multiclonal treatments, suggesting high evolvability of traits involved in parasite attachment onto hosts (i.e., encystment). A comparison of the performance of evolved and unevolved (control) parasite populations against their common ancestral host did not reveal parasite attenuation. Our results exemplify the ability of chytrid parasites to adapt rapidly to new hosts, while providing experimental evidence that genetic diversity in host populations grants increased resistance to disease by hindering parasite adaptation

Light intensity and spectral distribution affect chytrid infection of cyanobacteriaviamodulation of host fitness

Light gradients are an inherent feature in aquatic ecosystems and play a key role in shaping the biology of phytoplankton. Parasitism by chytrid fungi is gaining increasing attention as a major control agent of phytoplankton due to its previously overlooked ubiquity, and profound ecological and evolutionary consequences. Despite this interest, if and how light conditions modulate phytoplankton chytridiomycosis remains poorly studied. We investigated life-history traits of a chytrid parasite,Rhizophydium megarrhizum, under different light intensities and spectral compositions when infecting two closely related planktonic cyanobacteria with different light-harvesting strategies:Planktothrix rubescensandP. agardhii. In general, parasite transmission was highest under light conditions (both intensity and quality) that maximized growth rates for uninfected cyanobacteria. Chytrid encystment on hosts was significantly affected by light intensity and host strain identity. This likely resulted from higher irradiances stimulating the increased discharge of photosynthetic by-products, which drive parasite chemotaxis, and from strain-specific differences at the cell-surface. Comparisons of parasite transmission and host growth rates under different light conditions suggest the potential for epidemic development at higher irradiances, whereas host and parasite could coexist without epidemic outbreaks at lower light levels. These results illustrate the close relationship between parasite transmission and host fitness, which is ultimately modulated by the external environment

Adaptation of a chytrid parasite to Its cyanobacterial host Is hampered by host intraspecific diversity

Experimental evolution can be used to test for and characterize parasite and pathogen adaptation. We undertook a serial-passage experiment in which a single parasite population of the obligate fungal (chytrid) parasite Rhizophydium megarrhizum was maintained over a period of 200 days under different mono- and multiclonal compositions of its phytoplankton host, the bloom-forming cyanobacterium Planktothrix. Despite initially inferior performance, parasite populations under sustained exposure to novel monoclonal hosts experienced rapid fitness increases evidenced by increased transmission rates. This demonstrates rapid adaptation of chytrids to novel hosts and highlights their high evolutionary potential. In contrast, increased fitness was not detected in parasites exposed to multiclonal host mixtures, indicating that cyanobacterial intraspecific diversity hampers parasites adaptation. Significant increases in intensity of infection were observed in monoclonal and multiclonal treatments, suggesting high evolvability of traits involved in parasite attachment onto hosts (i.e., encystment). A comparison of the performance of evolved and unevolved (control) parasite populations against their common ancestral host did not reveal parasite attenuation. Our results exemplify the ability of chytrid parasites to adapt rapidly to new hosts, while providing experimental evidence that genetic diversity in host populations grants increased resistance to disease by hindering parasite adaptation

Chytrid parasitism facilitates trophic transfer between bloom-forming cyanobacteria and zooplankton (Daphnia)

Parasites are rarely included in food web studies, although they can strongly alter trophic interactions. In aquatic ecosystems, poorly grazed cyanobacteria often dominate phytoplankton communities, leading to the decoupling of primary and secondary production. Here, we addressed the interface between predator-prey and host-parasite interactions by conducting a life-table experiment, in which four Daphnia galeata genotypes were maintained on quantitatively comparable diets consisting of healthy cyanobacteria or cyanobacteria infected by a fungal (chytrid) parasite. In four out of five fitness parameters, at least one Daphnia genotype performed better on parasitised cyanobacteria than in the absence of infection. Further treatments consisting of purified chytrid zoospores and heterotrophic bacteria suspensions established the causes of improved fitness. First, Daphnia feed on chytrid zoospores which trophically upgrade cyanobacterial carbon. Second, an increase in heterotrophic bacterial biomass, promoted by cyanobacterial decay, provides an additional food source for Daphnia. In addition, chytrid infection induces fragmentation of cyanobacterial filaments, which could render cyanobacteria more edible. Our results demonstrate that chytrid parasitism can sustain zooplankton under cyanobacterial bloom conditions, and exemplify the potential of parasites to alter interactions between trophic levels

Nanoplastics modulate the outcome of a zooplankton–microparasite interaction

1. The accumulation and degradation of plastic waste in freshwater bodies poses a threat to aquatic biota. Microplastics (<5 mm) can transfer upwards in food chains and have been shown to induce deleterious effects on important players of freshwater ecosystems, including zooplankton. 2. A smaller category of microplastic particles, the so‐called nanoplastics (≤100 nm) raise special concern due to their ability to act at sub‐cellular and molecular levels. Despite growing knowledge of their effects on physiological traits of individual species, the way they affect interactions between species remains largely unexplored. 3. We studied the effects of nanoplastics on host–parasite interactions by exposing the zooplankton host Daphnia galeata × longispina to the parasitic yeast Metschnikowia bicuspidata without plastic and at two different concentrations of polystyrene nanoplastic beads (100 nm): 5 and 20 mg/L. 4. Both concentrations of nanoplastics increased the proportion of infected hosts; at the higher concentration, however, elevated rates of host mortality and impaired spore production cancelled out the parasite's advantage. Consequently, parasite success was greatest at the lower level of nanoplastic exposure. 5. Infection by Metschnikowia greatly reduced host lifespan and total offspring production (regardless of nanoplastic exposure), but only decreased the proportion of successfully reproducing hosts when Daphnia were additionally exposed to nanoplastics. Nanoplastics alone did not cause such a reduction in host fitness parameters: instead, the lower concentration increased lifetime offspring production by about 50%, suggesting hormesis. 6. Given that parasitism is a ubiquitous lifestyle in nature and that parasites can play important roles in the shaping and functioning of ecosystems, these results highlight the importance of including interactions between host and parasite species as alternative ecotoxicological endpoints to better assess the ecological consequences of plastic pollution

Ecotoxicity assessment of microcystins from freshwater samples using a bioluminescent cyanobacterial bioassay

The hepatotoxic cyanotoxins microcystins (MCs) are emerging contaminants naturally produced by cyanobacteria. Yet their ecological role remains unsolved, previous research suggests that MCs have allelopathic effects on competing photosynthetic microorganisms, even eliciting toxic effects on other freshwater cyanobacteria. In this context, the bioluminescent recombinant cyanobacterium Anabaena sp. PCC7120 CPB4337 (hereinafter Anabaena) was exposed to extracts of MCs. These were obtained from eight natural samples from freshwater reservoirs that contained MCs with a concentration range of 0.04–11.9 μg MCs L−1. MCs extracts included the three most common MCs variants (MC-LR, MC-RR, MC-YR) in different proportions (MC-LR: 100–0%; MC-RR: 100–0%; MC-YR: 14.2–0%). The Anabaena bioassay based on bioluminescence inhibition has been successfully used to test the toxicity of many emerging contaminants (e.g., pharmaceuticals) but never for cyanotoxins prior to this study. Exposure of Anabaena to MCs extracts induced a decrease in its bioluminescence with effective concentration decreasing bioluminescence by 50% ranging from 0.4 to 50.5 μg MC L−1 in the different samples. Bioluminescence responses suggested an interaction between MCs variants which was analyzed via the Additive Index method (AI), indicating an antagonistic effect (AI < 0) of MC-LR and MC-RR present in the samples. Additionally, MC extracts exposure triggered an increase of intracellular free Ca2+ in Anabaena. In short, this study supports the use of the Anabaena bioassay as a sensitive tool to assess the presence of MCs at environmentally relevant concentrations and opens interesting avenues regarding the interactions between MCs variants and the possible implication of Ca2+ in the mode of action of MCs towards cyanobacteri

Seasonality of parasitic and saprotrophic zoosporic fungi: linking sequence data to ecological traits

Zoosporic fungi of the phylum Chytridiomycota (chytrids) regularly dominate pelagic fungal communities in freshwater and marine environments. Their lifestyles range from obligate parasites to saprophytes. Yet, linking the scarce available sequence data to specific ecological traits or their host ranges constitutes currently a major challenge. We combined 28 S rRNA gene amplicon sequencing with targeted isolation and sequencing approaches, along with cross-infection assays and analysis of chytrid infection prevalence to obtain new insights into chytrid diversity, ecology, and seasonal dynamics in a temperate lake. Parasitic phytoplankton-chytrid and saprotrophic pollen-chytrid interactions made up the majority of zoosporic fungal reads. We explicitly demonstrate the recurrent dominance of parasitic chytrids during frequent diatom blooms and saprotrophic chytrids during pollen rains. Distinct temporal dynamics of diatom-specific parasitic clades suggest mechanisms of coexistence based on niche differentiation and competitive strategies. The molecular and ecological information on chytrids generated in this study will aid further exploration of their spatial and temporal distribution patterns worldwide. To fully exploit the power of environmental sequencing for studies on chytrid ecology and evolution, we emphasize the need to intensify current isolation efforts of chytrids and integrate taxonomic and autecological data into long-term studies and experiments.Alliance of German Science Organizations///AlemaniaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Seasonality of parasitic and saprotrophic zoosporic fungi: linking sequence data to ecological traits

Zoosporic fungi of the phylum Chytridiomycota (chytrids) regularly dominate pelagic fungal communities in freshwater and marine environments. Their lifestyles range from obligate parasites to saprophytes. Yet, linking the scarce available sequence data to specific ecological traits or their host ranges constitutes currently a major challenge. We combined 28 S rRNA gene amplicon sequencing with targeted isolation and sequencing approaches, along with cross-infection assays and analysis of chytrid infection prevalence to obtain new insights into chytrid diversity, ecology, and seasonal dynamics in a temperate lake. Parasitic phytoplankton-chytrid and saprotrophic pollen-chytrid interactions made up the majority of zoosporic fungal reads. We explicitly demonstrate the recurrent dominance of parasitic chytrids during frequent diatom blooms and saprotrophic chytrids during pollen rains. Distinct temporal dynamics of diatom-specific parasitic clades suggest mechanisms of coexistence based on niche differentiation and competitive strategies. The molecular and ecological information on chytrids generated in this study will aid further exploration of their spatial and temporal distribution patterns worldwide. To fully exploit the power of environmental sequencing for studies on chytrid ecology and evolution, we emphasize the need to intensify current isolation efforts of chytrids and integrate taxonomic and autecological data into long-term studies and experiments.</p

Limited Stability of Microcystins in Oligopeptide Compositions of Microcystis aeruginosa (Cyanobacteria): Implications in the Definition of Chemotypes

The occurrence of diverse oligopeptides in cyanobacteria, including the cyanotoxins microcystins, has been recently used to classify individual clones into sub-specific oligopeptide chemotypes, whose composition and dynamics modulate microcystin concentrations in cyanobacterial blooms. Cyanobacterial chemotyping allows the study of the ecology of chemotypical subpopulations, which have been shown to possess dissimilar ecological traits. However, the stability of chemotypes under changing abiotic conditions is usually assumed and has not been assessed in detail. We monitored oligopeptide patterns of three strains of Microcystis aeruginosa under different nutrient and light conditions. MALDI-TOF MS revealed alterations in the microcystins signatures under N and P poor conditions and high light intensities (150 and 400 μmol photons m−2s−1). Variations in the general oligopeptide composition were caused by a gradual disappearance of microcystins with low relative intensity signals from the fingerprint. The extent of such variations seems to be closely related to physiological stress caused by treatments. Under identical clonal compositions, alterations in the oligopeptide fingerprint may be misinterpreted as apparent shifts in chemotype succession. We discuss the nature of such variations, as well as the consequent implications in the use of cyanobacterial chemotyping in studies at the subpopulation level and propose new guidance for the definition of chemotypes as a consistent subpopulation marker