Chytridiomycosis of Marine Diatoms—The Role of Stress Physiology and Resistance in Parasite-Host Recognition and Accumulation of Defense Molecules

Abstract

Little is known about the role of chemotaxis in the location and attachment of chytrid zoospores to potential diatom hosts. Hypothesizing that environmental stress parameters affect parasite-host recognition, four chytrid-diatom tandem cultures (Chytridium sp./Navicula sp., Rhizophydium type I/Nitzschia sp., Rhizophydium type IIa/Rhizosolenia sp., Rhizophydium type IIb/Chaetoceros sp.) were used to test the chemotaxis of chytrid zoospores and the presence of potential defense molecules in a non-contact-co-culturing approach. As potential triggers in the chemotaxis experiments, standards of eight carbohydrates, six amino acids, five fatty acids, and three compounds known as compatible solutes were used in individual and mixed solutions, respectively. In all tested cases, the whole-cell extracts of the light-stressed (continuous light exposure combined with 6 h UV radiation) hosts attracted the highest numbers of zoospores (86%), followed by the combined carbohydrate standard solution (76%), while all other compounds acted as weak triggers only. The results of the phytochemical screening, using biomass and supernatant extracts of susceptible and resistant host-diatom cultures, indicated in most of the tested extracts the presence of polyunsaturated fatty acids, phenols, and aldehydes, whereas the bioactivity screenings showed that the zoospores of the chytrid parasites were only significantly affected by the ethanolic supernatant extract of the resistant hosts.

Integrating chytrid fungal parasites into plankton ecology: research gaps and needs

“…Experimental work with isolates is essential to study chytrid biology and that of their hosts in its numerous facets, such as the ecophysiology of chytrid infection, or its underlying mechanisms at the cellular level. For example, isolates can be used to undertake chemotactic assays based on live‐cell imaging coupled with microfluidics (Rusconi et al ., ; Scholz et al ., ) to determine zoospore swimming properties or chemotaxis in response to biotic or abiotic factors. Formulation of hypotheses about the interaction between chytrids and other trophic levels (e.g.…”

“…These compounds include amino acids, saccharides and other carbohydrates (Halsall, 1976;Orpin and Bountiff, 1978;Mitchell and Deacon, 1986;Muehlstein et al, 1988;Donaldson and Deacon, 1993;Moss et al, 2008). Whole-cell extracts and mixtures of carbohydrates (xylose, ribose, rhamnose, mannose, fucose, glucose and arabinose) attracted more zoospores as compared to single compounds alone (Scholz et al, 2017), suggesting that multiple attractants drive chemotaxis and that they act synergistically. Altogether, this suggests that taxis in zoosporic parasites might not be specific in terms of host selection and is consistent with observations that zoospore attachment to hosts can be reversible in some taxa (Doggett and Porter, 1995).…”

The oomycete Lagenisma coscinodisci hijacks host alkaloid synthesis during infection of a marine diatom

“…This step is paramount to the completion of the life cycle, allowing the parasite dissemination to new algal cells. Signaling cues are involved in the chemotaxis of the flagellated parasitic forms 17 , but the cellular effectors of oomycete infection of microalgae are unknown. The cultivation of the parasite and its host in an in vitro pathosystem can enable the investigation of infection mechanism, as demonstrated for the oomycete Eury-chasma dicksonii that broadly infects seaweeds 15,18,19 .…”

Progress in Microbial Ecology in Ice-Covered Seas

“…Historical culturing-based studies have resulted in the description of hundreds of marine fungal species (Johnson and Sparrow 1961;Kohlmeyer and Kohlmeyer 2013), whose global distribution remains largely unexplored. The more-recent application of molecular methods to studies of marine ecosystem ecology helps to circumvent challenges associated with visual classification and have identified an abundant and dynamic fungal community in subseafloor sediment (Orsi et al 2013), in association with pelagic marine snow (Bochdansky et al 2017), in coastal marine habitats (Ueda et al 2015;Picard 2017) as parasites of phytoplankton (Hanic et al 2009;Lepelletier et al 2014;Hassett and Gradinger 2016;Jephcott et al 2016;Scholz et al 2017a, b) and metazoans (Polglase 1980;Mclean and Porter 1982;Bower 1987;Shields 1990;Rahimian 1998). Relative to lower latitudes, knowledge of Arctic marine fungi is considerably less developed, in part due to the logistical constraints and inaccessibility of sampling sites.…”