The demand for natural food colorants is growing as consumers question the use of artificial colorants more and more. The phycobiliprotein C-phycocyanin of Arthospira platensis is used as a natural blue colorant in certain food products. The thermoacidophilic red microalga Cyanidioschyzon merolae might provide an alternative source of phycocyanin. Cyanidioschyzon merolae belongs to the order Cyanidiophyceae of the phylum Rhodophyta. Its natural habitat are sulfuric hot springs and geysers found near volcanic areas in, e.g., Yellowstone National Park in the USA and in Java, Indonesia. It grows optimally at a pH between 0.5 and 3.0 and at temperatures up to 56 °C. The low pH at which C. merolae grows minimizes the risk of microbial contamination and could limit production loss. As C. merolae lacks a cell wall, phycocyanin with a high purity number of 9.9 could be extracted by an osmotic shock using a simple ultrapure water extraction followed by centrifugation. The denaturation midpoint at pH 5 was 83 °C, being considerably higher than the A. platensis phycocyanin (65 °C). The C. merolae phycocyanin was relatively stable at pH 4 and 5 up to 80 °C. The high thermostability at slightly acidic pH makes the C. merolae phycocyanin an interesting alternative to A. platensis phycocyanin as a natural blue food colorant.

Sporulation is an essential part of the life cycle of the industrially important filamentous fungus Aspergillus niger. The formation of conidiophores, spore-bearing structures, requires remodelling of the fungal cell wall, as demonstrated by the differences in carbohydrate composition of cell walls of vegetative mycelium and spores. Glycoside hydrolases that are involved in this process have so far remained unidentified. Using transcriptome analysis, we have identified genes encoding putative cell-wall-modifying proteins with enhanced expression in sporulating aerial mycelium compared to vegetative mycelium. Among the most strongly induced genes were those encoding a protein consisting of a putative chitin binding module (CBM14) and the chitinolytic enzymes NagA, CfcI and CtcB. Reporter studies showed that the N-acetyl-b-hexosaminidase gene nagA was expressed both in vegetative hyphae and in aerial structures (aerial hyphae, conidiophores and conidia) upon starvation. In contrast, promoter activities of the chitinase genes ctcB and cfcI were specifically localized in the conidiophores and conidia. CtcB is an endochitinase and CfcI releases monomers from chitin oligosaccharides: together these enzymes have the potential to degrade chitin of the fungal cell wall. Inactivation of both the cfcI and ctcB genes affected neither radial growth rate, nor formation and germination of spores. The amount of chitin in the spore walls of a DcfcIDctcB double deletion strain, however, was significantly increased compared with the wild-type, thus indicating that CfcI and CtcB indeed modify the A. niger cell walls during sporulation. These novel insights in the sporulation process in aspergilli are of strong scientific relevance, and also may aid industrial strain engineering.

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