Growth competition between Microcystis aeruginosa and Quadrigula chodatii under controlled conditions

Cyanobacteria are the dominant bloom-forming species in Lake Taihu. Understanding the competition among algae is important to control strategies for bloom formation and outbreaks in freshwater ecosystems. In this study, we demonstrate that the cyanobacterium Microcystis aeruginosa PCC7820 and the green alga Quadrigula chodatii FACHB-1080 exhibit a strong competitive inhibitory relationship under co-culture conditions, with the latter strain inhibiting the former. Several factors influence the competitive relationship between the two species, including nutrition, temperature, and organic/inorganic compounds. Q. chodatii strongly inhibited M. aeruginosa growth through the inhibition of nitrogen utilization during co-culture. Temperature was also an influential determinant of the competition capacity between the two species under eutrophic conditions: at lower temperatures (15 A degrees C), M. aeruginosa grew better than Q. chodatii, but the difference was not significant (p > 0.05), whereas at higher temperatures (25 A degrees C, 35 A degrees C), Q. chodatii grew significantly better than M. aeruginosa (p < 0.05). Furthermore, the Q. chodatii filtrate strongly inhibited the growth of M. aeruginosa. An analysis of the crude extracts of the algae culture filtrates from uni- and co-cultures using gas chromatography mass spectrometry (GC/MS) indicated that algal metabolites, such as dibutyl phthalate and beta-sitosterol, might play a key role in the competition between algae.