Effects of light and nutrients on the growth of algal cells revealed by a microfluidic platform*

Photosynthetic micro-organisms play important roles in shaping and balancing aquatic ecosystems. One emerging environmental problem caused by these organisms is Harmful Algal Bloom (HAB), where the sudden growth of cyanobacterium or microalga disrupts lake or coastal ecosystems.  In order to elucidate the effects of complex environmental conditions (physical, chemical, and biological) under which HABs occur, we developed a micro-scale light gradient generator, which, together with a microfluidics chemical gradient generator, enabled the quantitative study of algal growth under various environmental cues. In this presentation, we systematically studied the growth kinetics of Chlamydomonas reinhardtii, under a light intensity gradient, a nitrogen (N) concentration gradient, and combined light and N gradients. The combinatory effect of light and N on algal growth shed light on the investigation into the interplay between photosynthesis and nitrogen metabolism. Our work revealed that the growth rate of the microalgae was significantly regulated by the light intensity and nitrogen concentration, and demonstrated the enabling ability of the platform in fast screening of environmental factors for algal growth.