Early detection of protozoan grazers in algal biofuel cultures

Future micro-algal biofuels will most likely be derived from open-pond production systems. These are by definition open to “invasion” by grazers, which could devastate micro-algal mass-cultures. There is an urgent requirement for methodologies capable of early detection and control of grazers in dense algal cultures. In this study a model system employing the marine alga Nannochloropsis oculata was challenged by grazers including ciliates, amoebae and a heterotrophic dinoflagellate. A FlowCAM flow-cytometer was used to detect all grazers investigated (size range <20–>80 μm in length) in the presence of algae. Detection limits were <10 cells ml−1 for both “large” and “small” model grazers, Euplotes vannus (80 × 45 μm) and an unidentified holotrichous ciliate (∼18 × 8 μm) respectively. Furthermore, the system can distinguish the presence of ciliates in N. oculata cultures with biotechnologically relevant cell densities; i.e. >1.4 × 108 cells ml−1 (>0.5 g l−1 dry wt.).