Is cell composition related to the phylogenesis of microalgae? An investigation using Hierarchical Cluster Analysis of Fourier Transform Infrared spectra of whole cells

Fourier Transform Infra-Red (FTIR) spectroscopy was used to investigate whether algae belonging to the green evolutionary lineage and algae belonging to the red evolutionary lineage consistently differ for their biomass composition and for the way their composition responds to changes in NO3− availability. For this purpose, the FTIR spectra of eleven algal species cultured in media containing different amount of NO3− were subjected to Hierarchical Cluster Analysis (HCA). The same analysis was conducted on the differential FTIR spectra of cells grown at different NO3− concentrations. Although the organic composition of cells was affected by the availability of NO3−, the analysis of its change did not elicit a clear relationship with the phylogenetic position of the species used. However, when the two evolutionary lineages, and not the individual species, are compared, some differences emerge: the species belonging to the green lineage reorganize their biomass composition similarly in response to variations in N availability, whereas the species of the red lineage modulate their allocation patterns more heterogeneously. This difference may contribute to the ecological fitness of microalgae and may have had an influence on the evolutionary trajectories of phytoplankton groups.

► Fourier Transform Infra-Red (FTIR) can be used to obtain a snapshot of cell composition. This technique is a potentially powerful tool for the investigation of species composition and of the ecological and evolutionary history of organisms.
► Algae of the red evolutionary lineage are rather heterogeneous with respect to changes of their C allocation patterns in response to changes in NO3− availability. However, the level of reduction of their biomass is modified similarly in different species. For species of the green lineages, the responses to nutritional changes are more homogeneous, both in terms of composition and level of reduction.
► The different strategies for C allocation may have had an impact on the radiation and ecological success of the various phytoplankton groups.