Speaker
Description
Bulk spectroscopic measurements of photosynthetic light-harvesting complexes report ensemble-averaged properties that often obscure the heterogeneity and dynamic behaviour present at the level of individual complexes. Single-molecule fluorescence spectroscopy provides access to this hidden complexity through measurements of fluorescence intensity and lifetime; however, interpreting raw intensity–lifetime distributions can be challenging because broad, overlapping populations frequently appear visually as only one or two states. Fucoxanthin chlorophyll protein (FCP) is the major light-harvesting complex of diatoms and contains Lhcx subunits that are implicated in photoprotection under high-light conditions. We investigated the fluorescence dynamics of FCP complexes under different environmental conditions using single-molecule intensity and lifetime measurements, performing a comparative, pH-dependent study of two FCP types to examine how Lhcx modulates the photoprotective behaviour. To objectively extract the underlying emissive states, Gaussian mixture model (GMM) clustering was applied to the intensity–lifetime distributions. The optimal number of clusters was objectively determined using information criteria (AIC, BIC, ICL) and cluster-quality metrics to ensure statistical robustness. This approach revealed multiple emissive states beyond the simple two-state (quenched/unquenched) interpretation suggested by visual inspection, enabling direct comparison across datasets and highlighting how environmental conditions and Lhcx content influence the accessibility and stability of the various photophysical states within FCP.
