Abstract
The blastocladialean fungus Paraphysoderma sedebokerense parasitizes three microalgae species of economic interest: Haematococcus pluvialis, Chromochloris zofingiensis and Scenedesmus dimorphus. For the first time, we characterized the developmental stages of isolated fungal propagules in H. pluvialis co-culture, finding a generation time of 16 h. We established a patho-system to compare the infection in the three different host species for 48 h, with two different setups to quantify parameters of the infection and parameters of the parasite fitness. The prevalence of the parasite in H. pluvialis and C. zofingiensis cultures was 100%, but only 20% in S. dimorphus culture. The infection of S. dimorphus not only reached lower prevalence but was also qualitatively different; the infection developed preferentially on senescent cells and more resting cysts were produced, being consistent with a reservoir host. In addition, we carried out cross infection experiments and the inoculation of a mixed algal culture containing the three microalgae, to determine the susceptibility of the host species and to investigate the preference of P. sedebokerense for these microalgae. The three tested microalgae showed different susceptibility to P. sedebokerense, which correlates with blastoclad’s preference to the host in the following order: H. pluvialis > C. zofingiensis > S. dimorphus.
Highlights
We found prevalence values similar to the ones reported by Gutman et al [20], with inoculated H. pluvialis and C. zofingiensis cultures reaching 100% of prevalence, and a Scenedesmus species reaching prevalence of 20%
We investigated two parameters of the fitness starting with the same number of propagules inoculating 11:1 H. pluvialis, 1:1 C. zofingiensis and 4:1 S. dimorphus in different algal densities offering the same surface area, giving the same probability to the propagules to find a host (Figure 5)
C. zofingiensis? We suggest that it is related to cell size, since bigger host cells offer higher amounts of nutrients, as it was reported before that host cell size affects sporangium size and the number of spores produced [43]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The aquatic lower fungi belonging to Blastocladiomycota [1] and their close relatives, the better studied Chytridiomycota, have a high impact on phytoplankton dynamics [2,3], and commonly constitute a plague for microalgae in mass outdoor cultures [4,5,6]. Little is known about the life cycle, ecology and host range of many algal parasites [7]. The time needed to complete the life cycle of parasitic Chytridiomycota and Blastocladiomycota species, an essential parameter for understanding epidemics, has not been investigated and is only rarely reported from in situ studies [8,9,10,11,12]
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