Oceans cover 71 % of the planet’s surface and hold approximately 97 % of all Earth’s water. They mitigate weather extremes, generate oxygen, play a pivotal role in food security and store excess CO2. Over the last decades, they have been taking the brunt of climate change, resulting in less salinity, more acidity and increased warming. Climate change during the last few decades has led to important environmental modifications that may reduce nutrient availability for phytoplankton – microscopic organisms living at the surface of the ocean. This in turn, impacts on communities of species and the structure of ecological niches. Phytoplankton, autotrophic cells, play a pivotal role in the biological production of the oceans and are also responsible for roughly 40 % of the inorganic carbon fixation on Earth. The increase in the number of areas with low phytoplankton concentration in the future will drastically modify Earth’s carbon cycle.
A closer look at phytoplankton
The EU-funded MAPAPAIMA project, undertaken with the support of the Marie Skłodowska-Curie Actions (MSCA) programme, set out to investigate how phytoplankton can adapt to nutrient-limited conditions to survive. “This can help us understand the future of the phytoplankton community, the oceans and carbon fixation on Earth,” explains Mathias Girault, MSCA fellow. Girault adds: “Our research focused on a particular adaptation mechanism that is essential to the survival of numerous phytoplankton living in phosphate-limited environments. This mechanism involves an extracellular enzyme, alkaline phosphatase.” By using dissolved organic matter, this enzyme helps to diversify the phytoplankton’s sources of phosphorus ensuring better survival when this nutrient is in short supply.
New microfluidic platform
“The key achievement of the project was the development of an innovative and complete microfluidic platform and a lab-on-a-chip capable of successfully measuring alkaline phosphatase activity (APA) at the single cell level,” reports Girault. The platform consists of a series of image processing algorithms for the detection of target cells and sorting droplets as well as an autonomous image analysis system. It can help bring to light which species release alkaline phosphatase, to what extent and how future predictions on environmental conditions can be used to modify this enzymatic activity. Girault further highlights: “Through our analytical method, we were able to, for the first time, compare the APA of phytoplankton revivified from a sediment core to investigate the evolution and the adaptation in the APA expression as function of time.” The project discovered both inter-and intraspecific variabilities of APA, suggesting that in half a century, two different species of phytoplankton may have undergone similar adaptative evolution to face environmental changes and acquire ecological advantages.
Future research considerations
The project’s results represent initial steps in the detection of phytoplankton adaptation to nutrient limitation. When discussing what might come next, Girault notes that as a complete microfluidic system has been developed, a detailed view of the phytoplankton adaptation to nutrient limitation through time would be interesting to have. For example, by using some phytoplankton revivified from a deeper sediment layer. “Moreover, it would be interesting to revive more recent phytoplankton cells in order to detect the effects of human-induced nutrient discharges on the metabolic capability of phytoplankton cells,” concludes Girault.
MAPAPAIMA, phytoplankton, ocean, alkaline phosphatase, microfluidic platform, single cell level