Factors affecting the distribution and abundance of an unpigmented heterotrophic alga Prototheca richardsi

Abstract

SUMMARY 1. Numbers of the contramensal alga Prototheca richardsi were high in spring in two ponds used for breeding by anuran amphibians, but lower at other times of year and undetectable in two ponds not used by anurans. 2. Prototheca richardsi became abundant in the silt of eight experimental ponds which contained tadpoles, but remained undetectable in four otherwise identical ponds lacking tadpoles. 3. Prototheca richardsi numbers in laboratory microcosms remained stable for many days in sterile tap water, but declined with a half‐life of about 6 days in pond water at 20°C. 4. Further studies with microcosms using antibiotics and electron microscopy indicated that mortality of P. richardsi was caused primarily by pathogenic bacteria.

Prototheca richardsi, a pathogen of anuran larvae, is related to a clade of protistan parasites near the animal-fungal divergence

“…Mean cell size, utilization of carbon sources, and other growth parameters were consistent with classification of the anuran parasite in the genus Prototheca (Wong & Beebee, 1994). Furthermore, DNA-RNA hybridization studies (Beebee, 1991) showed stronger heterologous binding with nucleic acids from a green alga (genus Dunaliella) than with those from yeast or protozoa (genera (Wong & Beebee, 1994). Other protothecans can be cultured in uitro on Pvototheca isolation medium (PIM) (Pore, 1973), whereas P. richardsi shows only weak growth.…”

“…Algae of the genus Prototheca (Kruger, 1894) have spherical unpigmented cells 2-10 pm in diameter, distinctive cell walls, and refractive, inclusion-bearing vacuoles that restrict the cytoplasm to the edges of the cell (Pore, 1985(Pore, , 1986Beebee, 1991). Mean cell size, utilization of carbon sources, and other growth parameters were consistent with classification of the anuran parasite in the genus Prototheca (Wong & Beebee, 1994). Furthermore, DNA-RNA hybridization studies (Beebee, 1991) showed stronger heterologous binding with nucleic acids from a green alga (genus Dunaliella) than with those from yeast or protozoa (genera (Wong & Beebee, 1994).…”

“…Other protothecans can be cultured in uitro on Pvototheca isolation medium (PIM) (Pore, 1973), whereas P. richardsi shows only weak growth. Indeed, P. richardsi can be cultured successfully only in the guts of anuran larvae (Wong & Beebee, 1994), although it does replicate to a lesser extent in the guts of some other aquatic organisms such as the pond snail Limnaea stagnalis.…”

“…It mediates growth inhibition of tadpoles in the laboratory by means of interference competition (Beebee & Wong, 1992) and may play a role in determining the structure of natural anuran assemblages (Wong et aE., 1994; Bardsley & Beebee, 1998). Beebee & Wong (1993) showed that cells of P. richardsi are stimulated to replicate by passage through tadpole digestive systems, and that their occurrence in natural ponds is correlated with the presence of anuran larvae (Wong et al, 1994).…”

“…Prototheca richardsi (Wong & Beebee, 1994) is an enigmatic protist that has been implicated as a gut parasite of anuran larvae (e.g. Richards, 1962;Beebee, 1991).…”