Lanthanum elicitation on hypocrellin A production in mycelium cultures of Shiraia bambusicola is mediated by ROS generation

Rare earth elements(REEs)have been widely applied as efficient elicitors to improve production of biologically important secondary metabolites in plants.However,their effects on microbial secondary metabolites were seldom reported.In this study,lanthanum(LaCl3)was used as an elicitor in mycelium cultures of Shiraia bambusicola to stimulate the production of hypocrellin A(HA),a promising photosensitizer for anticancer photodynamic therapy.La^3+at 1.0 g/L not only increases HA content by 2.50-fold in mycelia,but stimulates HA exudation to the medium with the highest production(225.05 mg/L)on day 6.Further analysis shows that La^3+can induce the intracellular ROS(reactive oxygen species)accumulation with 2.33-fold higher contents of H2O2 in mycelium.HA production induced by La^3+treatment can be suppressed by ROS scavengers.Further analysis reveals that the elicitation of La^3+on HA accumulation is mediated by ROS generation to enhance expression of HA biosynthetical genes.The expression of ATP-binding cassette transporter gene(SbABC)for HA exudation is also regulated partially via ROS generated by NADPH oxidase.These results indicate that the enhanced HA production by La^3+might be mediated by ROS signaling pathway.Our results provide a basis for understanding REE elicitation on fungal metabolites and a practical biotechnological process for enhanced production of HA.

Lanthanum:A novel inducer for enhancement of fungal laccase production by Shiraia bambusicola

Fungal laccases are industrially important inducible enzymes extensively used in the delignification of lignocellulosics,detoxification of environmental wastes and decolorization of textile dyes.The discovery of new inducers is crucial for laccase productivity by filamentous fungi.In this study,a novel laccase-producing strain S8 from a bambusicolous fungus Shiraia bambusicola was identified by using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate)as laccase secretion indicator and native polyacrylamide gel electrophoresis.The corresponding full-length cDNA of laccase was cloned and characterized.The effect of lanthanum(LaCl_(3))on extracellular laccase activity was tested at the concentration from 0.2 to 2.0 g/L and at different addition time(day 1-4)in the mycelium culture.In the presence of 1.0 g/L La^(3+) at the beginning of the mycelium cultures,the highest laccase activity(2.7×10^(4) U/L)is reached after 10 days of cultivation,about tenfold higher compared with non-induced cultures.La^(3+) is shown to be a very strong inducer for fungal laccase activity with no inhibitory effect on fungal growth at the optimized concentration.In vivo,La^(3+) added to the mycelium culture not only promotes a continuous and high expression of laccase gene(lcc1),but also induces a rapid generation of signaling molecules including reactive oxygen species(ROS)and nitric oxygen(NO).Both the NO donor sodium nitroprusside(SNP)and exogenous hydrogen peroxide(H_(2)O_(2))potentiate La^(3+)-induced laccase activity and increase membrane permeability of hyphal cells.Moreover,the scavengers such as 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(cPTIO)for NO and vitamin C for ROS suppress the induction.These results suggest that these signals can mediate La^(3+)-induced laccase biosynthesis and its secretion.Our study provides a basis for understanding the induction mechanism of La^(3+) on laccase and a practical strategy for enhanced fungal laccase production.