A light–dark shift strategy derived from light-responded metabolic behaviors for polyketides production in marine fungus Halorosellinia sp

Influences of light on growth, reproduction and hypocrellin production by Shiraia sp. SUPER-H168

Light is a very important signal for fungi since it influences many different physiological responses. The effects of dark or light at different wavelengths on growth, reproduction and hypocrellins of Shiraia sp. SUPER-H168 were studied: dark, white, red, yellow, green, blue and purple. All incubations under different light conditions had significant stimulating effects on aerial hyphae and suppressing effects on hypocrellin biosynthesis compared with dark incubation. Under blue and purple light especially blue light, the colonies with profuse growth of aerial mycelium were formed. Hypocrellin production reached 13.73 mg per dish under dark condition, and decreased to 4.01 mg and 2.83 mg per dish under white and blue light, respectively. Light condition not only influenced hypocrellin production but also influenced the composition of hypocrellins. Four types of hyphae, namely surface, aerial, biofilm and penetrative hyphae, were observed by light microscopy and SEM. This study found that biofilm hyphae was so closely connected with production of secondary metabolites, and hypocrellins were only produced by biofilm hyphae. Light promoted sexual development and inhibited asexual reproduction, especially blue light strongly inhibited asexual development.

Improved hypocrellin A production in Shiraia bambusicola by light-dark shift

Hypocrellin A (HA) is a major bioactive perylenequinone from the fruiting body of Shiraia bambusicola used for the treatment of skin diseases and developed as a photodynamic therapy (PDT) agent against cancers and viruses. The mycelial culture of S. bambusicola under dark is a biotechnological alternative for HA production but with low yield. In this study, light and dark conditions were investigated to develop effective elicitation on HA production in the cultures. Our results showed the constant light at 200 lx stimulated HA production without any growth retardation of mycelia. A light/dark shift (24: 24 h) not only increased HA content in mycelia by 65%, but stimulated HA release into the medium with the highest total HA production 181.67 mg/L on day 8, about 73% increase over the dark control. Moreover, light/dark shifting induced the formation of smaller and more compact fungal pellets, suggesting a new effective strategy for large-scale production of HA in mycelium cultures. The light/dark shift up-regulated the expression levels of two reactive oxygen species (ROS) related genes including superoxide-generating NADPH oxidase (Nox) and cytochrome c peroxidase (CCP), and induced the generation of ROS. With the treatment of vitamin C, we found that ROS was involved in the up-regulated expression of key biosynthetical genes for hypocrellins and improved HA production. These results provide a basis for understanding the influence of light/dark shift on fungal metabolism and the application of a novel strategy for enhancing HA production in submerged Shiraia cultures.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.

Regulation of different polyketide biosynthesis by green light in an endophytic fungus of mangrove leaf

Light is an important environmental signal for many organisms. The light response reports of fungi usually focus on blue light and red light. Although the green light sensor has also been found in several fungi, the knowledge of the green light response in fungi is very limited. Halorosellinia sp. (No. 1403) is a light-sensitive endophytic fungus of mangrove leaf. In this study, we explored the specific effects of monochromatic blue light, red light, and green light on polyketides biosynthesis in Halorosellinia sp. (No. 1403), respectively. The major polyketides produced in Halorosellinia sp. (No. 1403) are octaketides (1403C and 1403R) and heptaketide (griseofulvin). All monochromatic light enhanced octaketide biosynthesis and inhibited heptaketide biosynthesis to some extent compared with the dark condition. Most prominently, the total production of octaketides was increased by 76%, and the production of heptaketide was decreased by 73% under green light in bioreactor. Therefore, green light can not only influence the secondary metabolism in fungi, but also it can influence different biosynthetic pathways in different ways. We speculate that the significant effect of green light on mangrove leaf endophytic fungus Halorosellinia sp. (No. 1403) may be a kind of environmental adaptation to plant photosynthesis.

Glucose-6-phosphate dehydrogenase as a target for highly efficient fatty acid biosynthesis in microalgae by enhancing NADPH supply

Oleaginous microalgae have great prospects in the fields of feed, nutrition, biofuel, etc. However, biomass and lipid productivity in microalgae remain a major economic and technological bottleneck. Here we present a novel regulatory target, glucose-6-phosphate dehydrogenase (G6PD) from the pentose phosphate pathway (PPP), in boosting microalgal lipid accumulation. G6PD, involved in the formation of NADPH demanded in fatty acid biosynthesis as reducing power, was characterized in oleaginous microalga Phaeodactylum tricornutum. In G6PD overexpressing microalgae, transcript abundance of G6PD increased by 4.4-fold, and G6PD enzyme activity increased by more than 3.1-fold with enhanced NADPH production. Consequently, the lipid content increased by 2.7-fold and reached up to 55.7% of dry weight, while cell growth was not apparently affected. The fatty acid composition exhibited significant changes, including a remarkable increase in monounsaturated fatty acids C16:1 and C18:1 concomitant with a decrease in polyunsaturated fatty acids C20:5 and C22:6. G6PD was localized to the chloroplast and its overexpression stimulated an increase in the number and size of oil bodies. Proteomic and metabolomic analyzes revealed that G6PD play a key role in regulating pentose phosphate pathway and subsequently upregulating NADPH consuming pathways such as fatty acid synthesis, thus eventually leading to lipid accumulation. Our findings show the critical role of G6PD in microalgal lipid accumulation by enhancing NADPH supply and demonstrate that G6PD is a promising target for metabolic engineering.