Certain intensely bitter flavanone glycosides occur in citrus fruits together with isomeric glycosides that are tasteless. The bitter compounds all contain the disaccharide -neohesperidose (2-O-q-lrhamnosyl-/3-D-glucose). The tasteless compounds contain an isomeric disaccharide, j3-rutinose (6-0a-L-rhamnosvi-3-D-glucose). When alterations are made at selected sites in the flavanone neohesperido-sides the product may be bitter, bittersweet, sweet, or tasteless. Corresponding changes made in the flavanone rutinosides usually result in tasteless compounds unless the rhamnose is removed from the 6position of glucose. Of particular interest in this series are the neohesperidosyl dihydrochalcones, several of which are intensely sweet. This paper reviews recent findings in this field.

Aspergillus nidulans and Penicillium chrysogenum produce specific cellular siderophores in addition to the well-known siderophores of the culture medium. Since this was found previously in Neurospora crassa, it is probably generally true for filamentous ascomycetes. The cellular siderophore of A. nidulans is ferricrocin; that of P. chrysogenum is ferrichrome. A. nidulans also contains triacetylfusigen, a siderophore without apparent biological activity. Conidia of both species lose siderophores at high salt concentrations and become siderophore dependent. This has also been found in N. crassa, where lowering of the water activity has been shown to be the causal factor. We used an assay procedure based on this dependency to reexamine the extracellular siderophores of these species. During rapid mycelial growth, both A. nidulans and P. chrysogenum produced two highly active, unidentified siderophores which were later replaced by a less active or inactive product--coprogen in the case of P. chrysogenum and triacetylfusigen in the case of A. nidulans. N. crassa secreted coprogen only. Fungal siderophore metabolism is varied and complex.

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