Abstract
BackgroundNitric oxide (NO) is a ubiquitous signaling mediator in various physiological processes. However, there are less reports concerning the effects of NO on fungal secondary metabolites. Hypocrellins are effective anticancer photodynamic therapy (PDT) agents from fungal perylenequinone pigments of Shiraia. NO donor sodium nitroprusside (SNP) was used as a chemical elicitor to promote hypocrellin biosynthesis in Shiraia mycelium cultures.ResultsSNP application at 0.01–0.20 mM was found to stimulate significantly fungal production of perylenequinones including hypocrellin A (HA) and elsinochrome A (EA). SNP application could not only enhance HA content by 178.96% in mycelia, but also stimulate its efflux to the medium. After 4 days of SNP application at 0.02 mM, the highest total production (110.34 mg/L) of HA was achieved without any growth suppression. SNP released NO in mycelia and acted as a pro-oxidant, thereby up-regulating the gene expression and activity of reactive oxygen species (ROS) generating NADPH oxidase (NOX) and antioxidant enzymes, leading to the increased levels of superoxide anion (O2−) and hydrogen peroxide (H2O2). Gene ontology (GO) analysis revealed that SNP treatment could up-regulate biosynthetic genes for hypocrellins and activate the transporter protein major facilitator superfamily (MFS) for the exudation. Moreover, SNP treatment increased the proportion of total unsaturated fatty acids in the hypha membranes and enhanced membrane permeability. Our results indicated both cellular biosynthesis of HA and its secretion could contribute to HA production induced by SNP.ConclusionsThe results of this study provide a valuable strategy for large-scale hypocrellin production and can facilitate further understanding and exploration of NO signaling in the biosynthesis of the important fungal metabolites.
Highlights
Nitric oxide (NO) is a ubiquitous signaling mediator in various physiological processes
sodium nitroprusside (SNP) application released NO and enhanced hypocrellin production After the application of SNP at 0.10 mM to 3-day-old cultures, we observed a rise of green fluorescence of NO indicator 4, 5-diaminofluorescein diacetate (DAF2-DA) in Shiraia mycelia, whereas the relative fluorescent ration was markedly decreased by NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline1-oxyl-3-oxide, indicating the release of NO in hyphae (Fig. 1a, b)
The influence of SNP on hypocrellins including hypocrellin A (HA) and HC, and elsinochrome (A, B and C) in the culture was detected by HPLC (Additional file 1: Figure S3)
Summary
Nitric oxide (NO) is a ubiquitous signaling mediator in various physiological processes. NO donor sodium nitroprusside (SNP) was used as a chemical elicitor to promote hypocrellin biosynthesis in Shiraia mycelium cultures. The endogenous NO generation was observed in S. bambusicola treated by fungal elicitors [8, 12] and Triton X-100 [13], the regulation roles of NO on fungal hypocrellin biosynthesis are still undetermined. As a follow-up to our efforts on enhancing hypocrellin production [9, 25] and elucidating the role of NO on secondary metabolite biosynthesis [13, 26], we examined the effects of SNP on Shiraia hypocrellin biosynthesis. This study presented a novel elicitor of hypocrellin production and shed light on the relational roles of NO on the biosynthesis of secondary metabolites
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