Contamination of microalgal cultures by rotifers is known to cause large losses in productivity. The factors that control population dynamics of rotifers in microalgal cultures were studied in controlled contamination experiments in laboratory cultures. These experiments revealed that rotifer growth rates increase with microalgae biomass at low rotifer population densities and declines with rotifer biomass as the rotifer population approaches a carrying capacity. Experimental results were used to construct a model that describes the impact of rotifer contamination on three types of large-scale microalgal cultures. The results of this model indicate that rotifer contamination causes a complete loss in productivity in open pond and closed photobioreactor cultivation systems. In contrast, losses in productivity are limited in thin layer cascade reactors because the rotifer population cannot achieve a sufficiently high population density to cause a crash of the culture. These results suggest that different cultivation systems respond differently to rotifer contamination.
Large-scale production of microalgae for biofuels is often hampered by contamination of cultures with predators that feed on microalgae. An important group of predators are ciliates. Some species of marine microalgae in natural ecosystems are known to produce chemicals that act as deterrents against predators. In this study, we tested whether these chemicals (trans,trans-2,4-decadienal, dimethyl sulfoniopropionate (DMSP), glycine betaine and proline) as well as a chemical analogue (methyl 3-(methylthio)propionate or MMP) can be used to control contamination of cultures of the microalga Chlamydomonas by the predatory ciliate Sterkiella. All chemicals were capable of rapidly eradicating the ciliates from a contaminated Chlamydomonas culture, but at a higher dose also had a negative effect on the microalga. For each chemical an optimal dose was determined at which ciliates were controlled and losses in microalgal biomass productivity were minimized (0.13 mM decadienal, 4.75 mM DMSP, 10 mM MMP, 250-300 mM proline and 250-2 300 mM glycine betaine). In the case of DMSP, MMP and proline, biomass productivity was even the same as that of a non-contaminated culture. The chemicals were also effective against other ciliates (Stylonychia notophora, Oxytricha sp. and 2 different Paramecium species). These chemicals therefore have potential to be used as natural pesticides to control contamination of microalgal cultures by ciliates. Of all chemicals tested, DMSP and MMP are the most promising because they are effective at a relatively low dose and have a limited negative effect on microalgal productivity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.