The PALMADS project argues that improved measurement of photosynthesis in low-density microalgae suspensions is crucial for science and society. Microalgae play a major role in the bioeconomy (producing high-value compounds), represent a vast photosynthetic biodiversity, and are key indicators of environmental change. Understanding their photosynthesis can improve agriculture, biotechnology, and ecosystem monitoring. In terrestrial plants, significant progress has been made through the combination of chlorophyll fluorescence and differential absorption spectrometry, enabling detailed studies of photosynthetic systems. However, these tools lack the sensitivity required for aquatic environments, where microalgae are often present at very low concentrations. This limitation prevents field measurements and restricts research to a small number of easily cultivated species, leaving a large portion of microalgae diversity unexplored.
To address this problem, the project proposes to develop a high-sensitivity absorption difference spectrometer capable of measuring photosynthesis in highly dilute samples. This concept builds upon previous work (ERC StG PhotoPHYTOMICS) that used electrochromic shift (ECS) – a signal reflecting the electric field generated across thylakoid membranes during photosynthesis – to probe photosynthetic activity. ECS signals vary among microalgal lineages, allowing researchers to distinguish and analyze different species, even within mixed samples. This approach has already shown promise: it has enabled the detection of species-specific photosynthetic signals in natural samples and highlighted allelopathic interactions between species. However, these experiments required sample concentration through filtration, which can damage sensitive organisms like dinoflagellates. The proposed innovation is an Integrating Sphere absorption difference Spectrometer (ISS), which increases the optical path length. The project aims at increasing sensitivity by up to 100 times compared to commercial instruments -which would be sufficient to work on high phytoplankton density, coastal, natural samples- 1000 times would allow working on low phytoplankton density, open ocean, samples. This would allow for ECS-based measurements in much more dilute samples, without harmful concentration steps.
The goal of PALMADs is to test the feasibility of such measurement on dilute samples and to determine whether there is potential for patenting or transfer from academia to industry. If so, further developments could provide a revolutionary tool for studying the diversity, mechanisms and ecological roles of microalgae photosynthesis in their natural environment.
