Hyperspectral reflectance imaging to establish non-invasive phenotyping markers in microalgae

Abstract Hyperspectral imaging is an information-rich, reflectance-based spectroscopic method for non-intrusive investigation of physiological and biochemical properties of various organisms from cellular to ecological levels. Although several recent works have used hyperspectral imaging combined with predictive models to estimate algal biomass and valuable pigments, utilizing the advantages of hyperspectral sensing to reveal key physiological spectral indices remains far less definitive in microalgae. Here we establish a procedure in which robust hyperspectral indices can be obtained based on differential spectral signatures in microalgae in a wide range of chlorophyll content of single species. Furthermore, in algal mixtures the most representative spectral bands are sensitive to the volumetric mixing ratio. We also identified the spectral differences that are associated with the loss of pigments (phycocyanin in Synechocystis sp.) or accumulation of valuable carotenoids (astaxanthin in Haematococcus sp.) under stress conditions. We extended the spectral analysis for separately measured single cultures of microalgae with a diverse pigment composition (e.g. Nannochloropsis sp., the coral endosymbiont algae Symbiodiniaceae) to identify distinctive pigment profiles. Based on our results, marked spectral regions of the difference spectra of various microalgae are proposed for the construction of non-invasive hyperspectral-based pigment indices, which can be applied as expedite markers in algal phenotyping.