Christine Schimek

Carotene derivatives in sexual communication of zygomycete fungi

Recognition between mating partners, early sexual morphogenesis and development are regulated by a family of beta-carotene derived signal compounds, the trisporoids, in zygomycete fungi. Mating type-specific precursors are released from the hyphae and exert their physiological effects upon compatible mating partners. In a cooperative synthesis pathway, later intermediates and finally trisporic acid are formed. All trisporoids occur in a number of derivatives. Trisporic acid and some precursors directly influence the transcription of genes involved in sexual development. This has been demonstrated for TSP3, encoding the carotene oxygenase involved in sexually induced cleavage of beta-carotene. Species specificity of mating despite a common and commonly recognized signaling system is maintained by several factors. Specific distribution and recognition patterns of the trisporoid derivatives and the proposed divergence in trisporoid synthesis pathways in diverse species play a role. The derivatives elicit vastly differing, partially mating type-specific responses during early sexual development. Another specificity factor is the realization of different regulation levels for the trisporoid synthesis enzymes in different species. Enzymes in the trisporoid synthesis pathway show remarkable variations in mating type-specific activity and the exact activation time during sexual development. This allows for the observed complex network of possible interactions, but at the same time forbids successful mating between dissimilar partners because the necessary transcripts or gene products are not available at the appropriate developmental stage.

Magnetoreception in microorganisms and fungi

The ability to respond to magnetic fields is ubiquitous among the five kingdoms of organisms. Apart from the mechanisms that are at work in bacterial magnetotaxis, none of the innumerable magnetobiological effects are as yet completely understood in terms of their underlying physical principles. Physical theories on magnetoreception, which draw on classical electrodynamics as well as on quantum electrodynamics, have greatly advanced during the past twenty years, and provide a basis for biological experimentation. This review places major emphasis on theories, and magnetobiological effects that occur in response to weak and moderate magnetic fields, and that are not related to magnetotaxis and magnetosomes. While knowledge relating to bacterial magnetotaxis has advanced considerably during the past 27 years, the biology of other magnetic effects has remained largely on a phenomenological level, a fact that is partly due to a lack of model organisms and model responses; and in great part also to the circumstance that the biological community at large takes little notice of the field, and in particular of the available physical theories. We review the known magnetobiological effects for bacteria, protists and fungi, and try to show how the variegated empirical material could be approached in the framework of the available physical models.

Production and derivate composition of trisporoids in extended fermentation of Blakeslea trispora

Trisporic acid, its precursors and derivatives are used within zygomycete fungi as communication signals and sexual regulators, and also influence the production rate of the parent compound, β-carotene. Cultivation parameters during growth and the trisporoid production phase of Blakeslea trispora were studied in two-step shake flask cultures and up-scaled fermentations. Comparison of various fermentation protocols allowed the definition of parameters governing trisporoid production. Highest yields were obtained when the initial growth phase allowed for both rapid growth and fast exhaustion of nitrogen and phosporous sources. Onset of trisporoid production is accompanied by a pH drop in the medium and triggered by nutrient limitation, nitrogen depletion being the most important factor. Supplementation of cultures with carbon at low concentration after onset of trisporoid production led to prolonged growth and higher final product accumulation. B. trispora produces trisporoids in two major series, B and C. During a first peak in trisporic acid accumulation, production of trisporic acid B exceeds that of trisporic acid C, which later accumulates at the expense of the trisporic acid B, indicating a variable regulation of the ratio between these metabolites. These data are valuable for tailoring production systems for enrichment of specific intermediates of this complex signal family.

11 – Genetic Regulation of Carotenoid Biosynthesis in Fungi

Fungal carotenoids are synthesized by the isoprenoid pathway with isopentenyl pyrophosphate as the general precursor. They are found in all divisions of the fungal realm, and several are at the edge of being exploited at an industrial scale for satisfying an increasing demand for carotenoid pigments, food and feed additives, and components of cosmetics and pharmaceuticals. Fungi as carotenoid source are highly appealing. At least prospectively, they should be easier amenable to genetic manipulation than plants, and thus will allow tailoring of specially designed substances. Genes for carotenoid synthesis were cloned from many different fungi. In order to stimulate further functional studies on genetic pathways for internal and environmental regulation of carotene synthesis, modification and degradation, an overview on the situation in the most thoroughly studied model organisms is presented. The role of carotenoids as antioxidants, light protective substances and as signalling compounds is discussed.

13 Evolution of Special Metabolism in Fungi: Concepts, Mechanisms, and Pathways

Metabolism is one of the basic features of life and, in several aspects, the evolution of metabolism certainly precedes the origin of cellular life forms. Focusing mainly on the evolution of exemplary special metabolite biosynthesis pathways in fungi, in this overview the biochemical and genetical mechanics and mechanisms underlying the existing ramifications are described and explained at the current level of understanding. Special attention is given to the evolution of proteins and metabolite function and the evolution of mechanisms to acquire, preserve, and maintain favourable traits within a given lineage. Within the latter field, such topics as gene coupling in functional linkage groups and the roles played by horizontal gene transfer and adaptive evolution are also addressed.