RESUMO
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.
Assuntos
Cercozoários/isolamento & purificação , Microalgas/parasitologia , Fotobiorreatores/parasitologia , Lagoas/parasitologia , Pseudópodes/fisiologia , Scenedesmus/parasitologia , Cercozoários/genética , Cercozoários/fisiologia , Cercozoários/ultraestrutura , DNA de Protozoário/genética , DNA Ribossômico/genética , Microalgas/crescimento & desenvolvimento , Microscopia Eletrônica de Transmissão , Filogenia , Pseudópodes/genética , Pseudópodes/ultraestrutura , Scenedesmus/crescimento & desenvolvimento , Alinhamento de Sequência , Análise de Sequência de DNA , Trofozoítos/ultraestruturaRESUMO
In order to reduce the flow resistance of the thin-film flat plat photobioreactor (FPPBR) and make it more suitable for mass microalgae cultivation, the channel diameter was modified to 0.06 m and the thin-film FPPBR consisted of 10 parallel shunt-wound channels. A thin-film FPPBR system with 100 modified FPPBRs was constructed and used for Chlorella sp. cultivation in desertification areas (Ordos, China) from July to September of 2018. The pressure drop of the modified FPPBR system decreased significantly and the microalgae showed much higher productivity. The pressure drop was about 11.8 kPa when the liquid velocity was 0.238 m s-1. The final biomass concentration and area productivity reached 2.01 g L-1 and 49.79 g m-2 day-1 respectively, and the yearly productivity of Chlorella sp. was estimated to be about 15.24 t ha-2 year-1. The results demonstrated that high productivity of Chlorella sp. could be achieved in the improved FPPBR system in desertification areas and the improved FPPBR system was feasible for mass cultivation of microalgae in the commercial application.