(648f) Invasion and Co-Existence of Phototrophic Microbes in a Synthetic Model System Mediated By Nitrogen Availability

Microalgae are widely regarded as a promising renewable and sustainable feedstock for the production of various valuable molecules, including biofuels. However, biological contamination has detrimentally affected biomass production and is therefore considered as a major obstacle for open-system microalgae cultivation¹. New methods are needed to greatly enhance microalgae resistance to biological invasion. One underexplored strategy is to leverage working principles established in ecology research, such as those governing invasion and species co-existence in complex natural biological systems².

In this work, we investigate how competition and resource availability affect the outcomes of mutual invasion in a synthetic phototrophic microbial system. The system consists of Chlorella vulgaris, a microalga studied extensively in biofuel research, and Synechocystis sp. PCC6803, a model cyanobacterium. In each experiment, a resident species is established in a semi-continuous culture and the other species is introduced at low cell density as a potential invader. It has been found that the availability of nitrate, the sole nitrogen source in this system, determines the composition of resulted new steady state. Specifically, with abundant nitrate, Synechocystis successfully establishes itself in C. vulgaris culture, becoming the numerically dominant species while driving the microalga into low cell density. When nitrate is provided at low concentrations, Synechocystis fails to invade C. vulgaris. Similarly, C. vulgaris can invade established Synechocystis culture when nitrate is limited. Interestingly, mutual invasion can occur and lead to stable co-existence of the two species under certain conditions. Together, these results provide insights on the driving forces and dynamics of phototrophic ecosystems, which could have important implications for the development of new biological control methods.

Keywords: Microalgae, cyanobacteria, nitrogen limitation, invasion, co-existence

References

1 Wang H, Zhang W, Chen L, Wang J, Liu T. The contamination and control of biological pollutants in mass cultivation of microalgae. Bioresour Technol, 2013, 128, 745-750.

2 Chesson P. Mechanisms of maintenance of species diversity. Annu. Rev. Ecol. Syst., 2000, 31, 343-366.

Acknowledgements

Chun Wan is grateful to Chinese Government Scholarship Council (CSC) for financial support with his study in the US.