Influence of the algal microbiome on biofouling during industrial cultivation of Nannochloropsis sp. in closed photobioreactors

Abstract Industrial cultivation of microalgae is becoming increasingly important, yet the process is still hampered by many factors, including contamination and biofouling of the algal reactors. We characterized a subset of microorganisms occurring in the broth and different biofilm stages of industrial scale photobioreactors applied for the cultivation of Nannochloropsis sp. A total of 69 bacterial strains were isolated, belonging to at least 24 different species. In addition, a green microalga was isolated and identified as Chlamydomonas hedleyi . The effect of C. hedleyi and 24 of the bacterial isolates on the productivity of Nannochloropsis was evaluated through growth and biofilm assays. C. hedleyi was shown to reduce growth and induce biofilm formation in Nannochloropsis . These effects were however indirect as they could be attributed to the bacteria associated to C. hedleyi and not C. hedleyi itself. Although most bacterial strains reported no effect, several were able to induce biofilm formation.