Home • Paraphysoderma sedebokerense JEL821 v1.0
Images of Paraphysoderma strain JEL821:
a) Amoeboid spores.
b) Developing sporangium with filamentous rhizoids (arrow) in pure culture. 
c) Later stage of sporangial development.
d) Thick-walled (arrow) resting spore.
e) Early germination stage of resting spore. Note walls have curled back (arrows) and endosporangium is beginning to emerge (compare with Physoderma germination (Figs. 3, 4. Sparrow et al. 1961).
Photos by Joyce E. Longcore.
Images of Paraphysoderma strain JEL821: a) Amoeboid spores. b) Developing sporangium with filamentous rhizoids (arrow) in pure culture. c) Later stage of sporangial development. d) Thick-walled (arrow) resting spore. e) Early germination stage of resting spore. Note walls have curled back (arrows) and endosporangium is beginning to emerge (compare with Physoderma germination (Figs. 3, 4. Sparrow et al. 1961). Photos by Joyce E. Longcore.

Paraphysoderma strain JEL821 is a chytrid-like fungus from the phylum Blastocladiomycota. The genus and species P. sedebokerensis was described from cultures of the green alga Haematococcus pluvialis, which is commercially grown to produce the keto-carotenoid astaxanthin to be used as a natural food coloring agent or nutraceutical (Hoffman et al. 2008). The host has two life cycle stages, a motile green stage with a gelatinous wall and a non-motile red stage with a thicker wall, which is the stage used to extract the astaxanthin. Paraphysoderma grows only on the non-motile stage of H. pluvialis, and cross-infection studies with other green algal species show that H. pluvialis is among its preferred host species (Gutman et al. 2009). Another strain of P. sedebokerensis is parasitic on cultures of Scenedesmus dimorphus, a candidate for biofuel production (Letcher et al. 2016) and on Desmococcus olivaceus (based on GenBank acc. #: KX180161), tested for use in bioremediation.

Paraphysoderma sedebokerensis has two types of sporangia, thin-walled vegetative and thick-walled resting sporangia. Its asexual propagules are unusual for most zoosporic fungi, in that they typically lack a flagellum and use amoeboid motion to crawl on the outside of the host to find a location for penetration (Hoffman et al. 2008). Strittmatter et al. (2016) have recently documented the presence of a previously unnoticed flagellated stage. These posteriorly uniflagellated spores were observed specifically after meiosis in resting sporangia (Letcher et al. 2016). Paraphysoderma occupies a unique phylogenetic position on the earliest diverging branch of the Blastocladiomycota as the sister genus to Physoderma, a diverse genus of 50 species known only as obligate parasites of vascular plants. Isolate JEL821 was isolated from a H. pluvialis culture in the United States, far from the geographic source of the type collection (Israel). DNA sequence data, however, show that it is 99% similar at the ITS ribosomal RNA region to the FD61 isolate studied by Letcher et al. (2016) which was considered conspecific with P. sedebokerensis.

Sequencing the Paraphysoderma genome will facilitate studies to understand the interaction between green algae and their fungal parasites. Algal cultures have a great potential for the production of compounds such as astaxanthin as well as energy-rich compounds that can serve as biodiesel. In addition, sequencing a pure culture of a basal member of the Blastocladiomycota provides an opportunity to address the phylogenetic placement of this deeply diverging branch of the Fungal Tree of Life (James et al. 2014).

References:

Gutman, J., A. Zarka, and S. Boussiba. (2009). The host-range of Paraphysoderma sedebokerensis, a chytrid that infects Haematococcus pluvialis. Eur. J. Phycol. 44: 509-515.

Hoffman, Y., C. Aflalo, A. Zarka, J. Gutman, T. Y. James, and S. Boussiba. (2008). Isolation and characterization of a novel chytrid species (Phylum Blastocladiomycota), parasitic on the green alga Haematococcus. Mycol. Res. 112: 70-81.

James, T. Y., T. M. Porter, and W. W. Martin. (2014). Blastocladiomycota. In D. J. McLaughlin, and J. W. Spatafora [eds]. pp. 177-207. The Mycota VII. Springer Verlag, Berlin.

Letcher, P. M., P. A. Lee, S. Lopez, M. Burnett, R. C. McBride, and M. J. Powell. (2016). An ultrastructural study of Paraphysoderma sedebokerense (Blastocladiomycota), an epibiotic parasite of microalgae. Fungal Biol. 120:324-337.

Sparrow, FK, J.E. Griffin, and R.M. Johns. 1961. Observations on chytridiaceous parasites of phanerogams. XI. A Physoderma on Agropyron repens. American Journal of Botany 48: 850-858.

Strittmatter, M., T. Guerra, J. Silva, and C. M. M. Gachon. (2016). A new flagellated dispersion stage in Paraphysoderma sedebokerense, a pathogen of Haematococcus pluvialis. J. Appl. Phycol. 28:1553-1558.