Critical assessment of protozoa contamination and control measures in mass culture of the diatom Phaeodactylum tricornutum.

The diatom Phaeodactylum tricornutum is considered a promising "cell factory" for high-value products fucoxanthin and EPA. But its potential has not been realized due largely to microbial contamination. In this study, seven protozoan strains were identified, of which a heterolobosean amoeba was identified as the most frequently occurring and destructive predator in P. tricornutum culture. The addition of 400 mg L NHHCO inhibited amoeba proliferation with little impact on algal growth. Halting culture mixing at night induced a hypoxia environment that further inhibited amoeba growth. Regardless of culture systems employed, a periodical supply of proper amounts of NHHCO alone or in combination with halting culture mixing at night may prevent or treat protozoa contamination in mass culture of P. tricornutum.