Polyols in the green algal class Trebouxiophyceae (Chlorophyta) - biochemical profiling and molecular characterization of biosynthetic mechanisms for a phylogenetic-(chemo)taxonomical classification

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Although most algae typically inhabit aquatic environments, some members of the green algal class Trebouxiophyceae colonize terrestrial habitats. The class can be subdivided by molecular approaches into the Chlorella-, Oocystis- and Trebouxia- lineages, the latter one consisting of mostly aeroterrestrial species. Compared to their aquatic relatives, these algae are generally exposed to much harsher environmental conditions. The capability to synthesize polyols such as ribitol is regarded as biochemical adaptation towards their challenging habitat as these substances generally contribute to desiccation and other stress tolerances. However, the Trebouxiophyceae are rarely studied concerning such stress metabolites, and their molecular phylogeny is still debated among experts. Knowledge about polyol distribution within this class is actually restricted to aeroterrestrial taxa. Therefore: I. A systematic biochemical profiling for polyol expression will clarify the question whether these compounds represent a phylogenetic-(chemo)taxonomical trait or evolved independently permitting algal water-to-land transitions in certain lineages. II. The enzymes and coding genes for polyol biosynthesis in the Trebouxiophyceae will be investigated for the first time. The Trebouxiophycean species Coccomyxa will be chosen as model organism to identify the genes for ribitol biosynthesis since its complete genome sequence has just been published. III. After identification of the key enzymes and genes for ribitol biosynthesis, its value as new molecular-taxonomical marker will be evaluated. The results will contribute to the ongoing discussion on species concepts for microalgae.