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Prototheca

Prototheca species are achlorophyllous algae with phylogenetic affinities to the genus Chlorella. To date only P. wickerhamii and P. zopfii have been involved in human or animal infections (Lass-Florl and Mayr 2007).

RG-1 organisms.

Morphological Description: 
Colonies are smooth, moist, white to cream and yeast-like. Cultures are sensitive to cycloheximide (actidione) and optimal growth occurs at 25-30C. Mycelium and conidia are absent. Vegetative cells are globose to ovoid, hyaline, varying in size from approximately 3-30 µm, and have a relatively thick and highly refractile wall. No budding cells are present; reproduction is by the development of large sporangia (theca) which contain from 2-20 or more small sporangiospores (endospores or autospores) which are asexually produced by nuclear division and cleavage of the cytoplasm.

Molecular Identification: 
ITS and D1/D2 sequencing is recommended (Wang et al. 2014).

Key Features: 
Achlorophyllous algae reproducing by sporangia (theca) and sporangiospores (autospores). Prototheca species which can be differentiated by assimilation tests and morphological criteria as outlined below. The API 20C yeast identification strip may be used for species identification.

References: 
Kaplan (1977), McGinnis (1980), Rippon (1988), Pore (1985), Ueno et al. (2005), Lass-Florl and Mayr (2007), Wang et al. (2014).

P. wickerhamii P. zopfii P. stagnora
Colony morphology Hemispheric, with
smooth margin
Flat, rough
corrugated margin
Flat, with smooth
margin
Cell diameter µm 3-10 7-10 7-14
Growth at 37C + + -
Glucose + + +
Trehalose + - -
L-propanol - + +/-
Acetate (pH 5) - + +/-
Galactose + - +
Capsule - - +

Antifungal Susceptibility: Prototheca wickerhamii (Australian National data); MIC µg/mL.
No <0.03 0.06 0.125 0.25 0.5 1 2 4 8 16 32 >64
AmB 9 3 3 2 1
VORI 7 2 4 1
POSA 7 1 2 4
ITRA 9 2 5 2

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