Effects of environmental parameters on chytrid infection prevalence of four marine diatoms: a laboratory case study

Abstract

Abstract:The influence of environmental factors on the infection susceptibility of four different marine diatom host species to chytrid infection was tested under laboratory conditions, using host and parasite isolates obtained from diverse coastal areas in north-west Iceland in 2015. Specifically, a total of 120 monoclonal marine diatom host cultures of Navicula, Nitzschia, Rhizosolenia and Chaeto ceros were exposed to their chytrid parasites Chytridium type I and Rhizophydium type I and II in Hellendahl glass staining jars which were subdivided in two compartments by nylon filters (mesh size 5 μm). ) and photoperiods (24 h dark, 8:16 h, 16:8 h light:dark and 24 h light) after 168 h exposure, using the one-factor-at-a-time method. In addition, growth rates and proline concentrations of the noninfected monoclonal host cultures were determined. In most cases, decreasing growth rates during the acclimatisation process to abiotic stressors were directly related to increases of proline in the host cells. Significant positive associations of infection densities to cell based proline concentrations were predominantly observed in the high-PFR assays and 24-h daylight treatments. At least for half of the tested host-parasite pairs, positive correlations of proline and parasite prevalence were found. In addition, chytrid abundance was also positively correlated with host densities of Navicula sp., Rhizosolenia sp. and Chaetoceros sp. Only in Nitzschia sp., was parasite density negatively associated with proline and showed no significant relationship to host densities, suggesting that other physiological/biochemical factors related to stress might have an impact on the susceptibility of this peculiar host diatom species.

Chytrid fungi distribution and co-occurrence with diatoms correlate with sea ice melt in the Arctic Ocean

“…In situ infection experiments of chytrid and diatom species under various stress conditions demonstrate a higher infection density under light-stress conditions and a positive infection prevalence for Chaetoceros at low temperature (5°C) 21,23 . In marine high-latitude environments, phytoplankton from north-west Iceland were prone to increased viral infection, predation and fungal parasitism under higher light and higher water temperatures 22 , this is consistent with sea ice melt conditions. In the Western Arctic, a link between chytrid occurrence and algal stress in relation to increased light availability was found, particularly for pennate diatoms like Pleurosigma and Navicula 16,41 .…”

“…Other abiotic parameters reported to influence chytrid distribution are light, temperature and/or nutrients 16,22 and indeed model flagellated fungi have been shown to possess a sophisticated set of chemotactic and photo-tactic responses allowing them to navigate in response to light and nutrient gradients (e.g., refs. 10,11 ).…”

“…[20][21][22][23] . In situ experiments, addressing the effect of abiotic and biotic factors on susceptibility of diatom to chytrid infections have shown an influence of light-stress and host densities 22,23 , factors which can potentially be driven by ice melt but this relationship has not been demonstrated from wider environmental sampling in ice melt conditions. In the Arctic Ocean, many of the diatom genera (e.g., Nitzschia, Pseudo-nitzschia, Chaetoceros) shown to be susceptible to chytrid infections include major contributors to phytoplankton biomass 24 .…”

Fitness and eco-physiological response of a chytrid fungal parasite infecting planktonic cyanobacteria to thermal and host genotype variation

“…Chytrids infecting phytoplankton have been reported in the past (Braun, 1856;Canter, 1947;Canter & Lund, 1948;Canter & Lund, 1951), but they are attracting renewed interest as accumulating evidence demonstrates their unexpected diversity and widespread distribution in pelagic marine, brackish and freshwater habitats worldwide (Grossart et al, 2016;Hassett & Gradinger, 2016;Lefèvre et al, 2008;Lepère et al, 2008). The lifecycle of chytrids is characterized by a free-swimming stage in the form of flagellated zoospores that are assumed to find suitable hosts in the water column by chemotaxis (Muehlstein et al, 1988;Scholz et al, 2017). Once encysted on their host, chytrids develop a rhizoid system that penetrates the host cell wall to extract nutrients from it.…”

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

“…Indications that zoospores locate their hosts through chemotaxis, with photosynthetic by-products (i.e. common carbohydrates) driving their attraction, further support this notion Hickman, 1967a, 1967b;Scholz et al, 2017). Indeed, chytrid infection has been shown to be hampered in the presence of pollutants that inhibit algal photosynthesis (Van den Wyngaert et al, 2013).…”