Remarkable enhancement of flavonoid production in a co-cultivation system of Isatis tinctoria L. hairy root cultures and immobilized Aspergillus niger

The dried roots of Isatis tinctoria L. are highly traded in the pharmaceutical industry due to their notable anti-influenza efficacy. For the first time, I. tinctoria hairy root cultures (ITHRCs) were co-cultured with two immobilized live GRAS (Generally Recognized as Safe) fungi, i.e. Aspergillus niger and Aspergillus niger, for the elevated production of pharmacologically active flavonoids. Immobilized A. niger (IAN) was exhibited as the superior elicitor in the plant-fungus co-cultivation system. The highest flavonoid production (3018.31 ± 48.66 μg/g DW) were achieved in IAN-treated ITHRCs under the optimal conditions of IAN spore concentration ca.10(4) spores/mL, temperature 30 °C, initial pH value of media 7.0 and time 72 h, which remarkably increased 6.83-fold relative to non-treated control (441.91 ± 7.35 μg/g DW). Also, this study revealed that IAN elicitation could trigger the sequentially transient accumulation of signal molecules and intensify the oxidative stress in ITHRCs, which both contributed to the up-regulated expression of associated genes involved in flavonoid biosynthetic pathway. Moreover, IAN could be reused at least five cycles with satisfactory performance. Overall, the coupled culture of IAN and ITHRCs is a promising and effective approach for the enhanced production of flavonoids, which allows for the improved applicability of these valuable compounds in pharmaceutical fields.