Single-Cell and Bulk Fluorescence Excitation Signatures of Seven Phytoplankton Species During Nitrogen Depletion and Resupply

Abstract

Phytoplankton play a vital role as primary producers in aquatic ecosystems. One common approach to classifying phytoplankton is fluorescence excitation spectroscopy, which leverages the variation in types and concentrations of pigments among different phytoplankton taxonomic groups. Here, we used a fluorescence imaging photometer to measure excitation ratios (''signatures'') of single cells and bulk cultures of seven differently pigmented phytoplankton species as they progressed from nitrogen N-replete to N-depleted conditions. Our objective was to determine whether N depletion alters the fluorescence excitation signature of each species and, if so, how quickly they recover when N (as nitrate) was resupplied, because these factors affect our ability to classify the species correctly. Of the seven species studied, only Proteomonas sulcata, a marine cryptophyte, showed measurable changes in single-cell fluorescence excitation ratios and bulk fluorescence excitation spectra. These changes were likely due to decreases in the cellular concentration of phycoerythrin, a N-rich pigment, as N became scarce. Within 3 h of resupply of N, fluorescence signatures began returning to pre-depletion values and were indistinguishable from N-replete cells by 80 h after resupply. These data suggest that our classification approach is robust for non-PE containing phytoplankton. PE-containing phytoplankton might exhibit systematic changes in their signatures depending on their level of N depletion, but this could be detected and the phytoplankton reclassified following a few hours of incubation in N replete conditions.

Diversification of light capture ability was accompanied by the evolution of phycobiliproteins in cryptophyte algae

“…Furthermore, because we used a broad light spectrum and PUR is scaled to the amount of light available at each wavelength, we can be confident that all of our strains had available to them the light that they could capture, and that PUR measurements were not phylogenetically biased. Because phenotypic plasticity of cellular concentrations of photopigments with respect to light and nutrients is known [62,63,77], future work on the relationship between pigment characteristics and light capture as resource acquisition would benefit from a reaction norm approach that considers more environments. Such a strategy potentially resolves the trade-off between environment-specific and common-garden phylogenetic comparisons.…”

Chlorophyll Fluorometer for Intelligent Water Sampling by a Small Uncrewed Aircraft System (sUAS)

“…The fluorescence of the chlorophyll-based reaction centers, photosystem I and photosystem II, has been the basis for detecting chlorophyll and, by extension, phytoplankton in water for many years 9 and our laboratories have previously used fluorescence for phytoplankton analysis. 10,11…”

“…The fluorescence of the chlorophyll-based reaction centers, photosystem I and photosystem II, has been the basis for detecting chlorophyll and, by extension, phytoplankton in water for many years 9 and our laboratories have previously used fluorescence for phytoplankton analysis. 10,11 Fluorescence is a useful tool for in situ analysis of phytoplankton in water, but in situ methods are not likely to soon replace laboratory analysis based on water sampling. This is because a laboratory can bring to bear many tools for analyzing the number density and speciation of phytoplankton and can also provide correlating information on the nutrient conditions and chemical composition of water, the presence of bacteria and viruses, and other factors that are difficult to measure using in situ methods.…”

Identification to species level of live single microalgal cells from plankton samples with matrix-free laser/desorption ionization mass spectrometry

“…The herein described method demands no phycological expert knowledge, once a single-cell profiling database is established, ideally as an open-source repository. Since only cultures in well-defined conditions have been investigated, future studies will implement various stress conditions, as those were shown to have a strong influence on the metabolic profile of a microalgal cell (Faulkner et al 2019;Driver et al 2015). The present approach that monitors the metabolome has the potential to generate data about the physiological state of the single cells and thus about the metabolic heterogeneity of a plankton population.…”