f Microbial contamination is the main cause of loss of biomass yield in microalgal cultures, especially under outdoor environmental conditions. Little is known about the identities of microbial contaminants in outdoor mass algal cultures. In this study, a new genus and species of vampyrellid amoeba, Vernalophrys algivore, is described from cultures of Scenedesmus dimorphus in open raceway ponds and outdoor flat-panel photobioreactors. This vampyrellid amoeba was a significant grazer of Scenedesmus and was frequently associated with a very rapid decline in algal numbers. We report on the morphology, subcellular structure, feeding behavior, molecular phylogeny, and life cycle. The new amoeba resembles Leptophrys in the shape of trophozoites and pseudopodia and in the mechanism of feeding (mainly by engulfment). It possesses two distinctive regions in helix E10_1 (nucleotides 117 to 119, CAA) and E23_1 (nucleotides 522 and 523, AG) of the 18S rRNA gene. It did not form a monophyletic group with Leptophrys in molecular phylogenetic trees. We establish a new genus, Vernalophrys, with the type species Vernalophrys algivore. The occurrence, impact of the amoeba on mass culture of S. dimorphus, and means to reduce vampyrellid amoeba contamination in Scenedesmus cultures are addressed. The information obtained from this study will be useful for developing an early warning system and control measures for preventing or treating this contaminant in microalgal mass cultures.
Some green microalgae, species of Scenedesmus, are being explored for biomass production because they grow rapidly and synthesize large amounts of protein, starch, and lipid (1), as well as pigments (2, 3). The biomass can be used in wastewater bioremediation, carbon capture, animal feed, and biofuels (4). The use of Scenedesmus has been hampered by the difficulties in cultivating the alga on a commercial scale, caused in part by microbial contamination and losses due to microbial or zooplankton predators (5, 6).The identification of microbial contaminants is a critical first step in developing an effective early warning system and control measures that prevent or treat contamination (7). Information about contaminants in Scenedesmus cultures is rather limited. Microbial contaminants reported in outdoor cultures of Scenedesmus include Spirillum-like bacteria (8); fungi, such as Chytridium (9) and Amoeboaphelidium protococcarum (7, 10, 11); and an opisthokont intracellular parasitoid, Aphelidium sp. (12, 13). In our environments in Arizona, amoebae, ciliates, and rotifers were the main eukaryotic contaminants in Scenedesmus cultures. In particular, a vampyrellid amoeba was found to have the most damaging impact, with the contamination of cultures by the amoeba often leading to rapid and almost complete loss of Scenedesmus in a few days.Vampyrellids are a group of naked filose amoebae with distinctive morphologies, ultrastructure, and body forms that include amoeboid trophozoites, large plasmodia, and digestive cysts (14,15). Since the initial studies in t...
