Sexual reproduction in pennate diatoms : physiology and chemistry of pheromones active in femtomolar concentration

Chemical communication is the oldest and most widespread form of communication between organisms ranging from unicellular microorganisms to mammals. It includes pheromone signaling for mate choice and is known even from diatoms, a highly diverse group of unicellular photosynthetic organisms. Studying their sexual reproduction and pheromone chemistry fosters our knowledge of the evolution of one of the most important primary producers in the oceans. In the following thesis the mate finding process and pheromone systems including pheromone structures are investigated of the two benthic living pennate diatoms Cylindrotheca closterium and Seminavis robusta. The pheromone mediated mating in C. closterium is described. The distinct partners of the opposite mating types (mt+ and mt−) needed for successful sexual reproduction are characterized by their function and the involvement of an attraction pheromone secreted by mt− cells is proven by a newly established bioassay. Two more pheromones are suggested to promote the sexual events but C. closterium seems to have a less complex pheromone system compared to S. robusta. Pheromone structures are investigated using LC-MS and GC-MS based metabolomics comparisons and bioassay-guided fractionation. Peptides involved in the sexual reproduction were identified. In S. robusta, sex-inducing pheromones (SIP) initiate and synchronize sexual events but their structure elucidation is challenging. Combining large-scale cultivation, labeling experiments and chemical derivatization with sophisticated tandem mass spectrometry and NMR analyses enabled the first structure elucidation of a SIP from a benthic diatom. SIP+ secreted by mt+ cells is composed of a cyclic heptapeptide with an extraordinary sulfated C-terminal β-hydroxy aspartic acid and acts in low femtomolar range to induce the release of the attraction pheromone diproline from mt− cells. The SIP− of mt− is also characterized and found to be of peptidic nature as well.