Prevention and control of parasitic contamination in industrial microalgae cultures

In the field of industrial microalgae production, the introduction of parasitic contaminants is an often-neglected topic, but one that represents a major risk with potentially significant financial implications. So far, no successful strategy exists to maintain a long-term stable cultivation environment in industrial photobioreactors. To create a strategy for preventing and controlling parasitic contamination, methods from synthetic ecology were used, replacing monocultures with mixed-biocoenoses. The goals were the identification of microbiotic ecosystems of potentially symbiotic bacteria and the utilization of synergistic effects between bacteria and algae to stabilize cultures. The final aim was to combine the findings with abiotic factors influencing the infections. As model organisms, the microalga Coelastrella vacuolata (formerly Scenedesmus vacuolatus) and the parasitic contaminant Amoeboaphelidium protococcarum were chosen. For this case, a correlation between infection rate and the chlorophyll a fluorescence in the culture was found. Algal co-cultures with specific bacteria were tested using the protecting effects of antiphytopathogenic, extracellular substances. This led to the bacterium Pseudomonas protegens and the naturally antipathogenic phenol 2,4-diacetylphloroglucinol (DAPG). Co-cultures with DAPG-producing P. protegens effectively inhibited the infection even though no quantifiable amounts of DAPG were found in the culture. Furthermore, abiotic influences on the infection process were identified, resulting in the implementation of a light–dark-cycle with induced anaerobic conditions in the dark phase. With these findings, conditions that inhibit the growth of parasitic contaminants could now be introduced preventively within standard cultivation procedures.