Morphological mutants of Gibberella fujikuroi for enhanced production of gibberellic acid

Understanding the Fermentation Potentiality For Gibberellic Acid (GA3) Production Using Fungi

Gibberellins represent an important group of potent phytohormones, growth-promoting, closely related diterpenoid acids biologically derived from tetracyclic diterpenoid hydrocarbon. Among these, gibberellic acid (GA3) has received the greatest attention. GA3 is a highly valued plant growth regulator which has various applications in agriculture. It is extensively used for beneficial effects including stem elongation, elimination of dormancy, sex expression, seed germination, flowering, and fruit senescence. Along with plants, many microbes are also producing GA3 as their secondary metabolite, and among these, fungi are reported to produce a higher amount of GA3. Fermentation technology based on submerged fermentation and solid-state fermentation for the production of GA3 has been used with its merits and demerits using Fusarium moniliforme fungus in the industry. Several mathematical models and optimization tools were also designed for enhancing the fermentative yield by researchers. The detailed analysis is essential to understand all the fermentation aspects, various unit parameters, process operation approaches, reduction in cost, and assessment of the possible uses of these models in the production of GA3 for higher yield. Recently, exclusive research is executed to lower down the production cost of GA3 approaching various strategies.

Endophytic Fusarium oxysporum GW controlling weed and an effective biostimulant for wheat growth

Wheat crop has to compete with several weeds including Avena fatua, a noxious weed that alone is responsible for 30-70% losses in the yield annually. Because of the environmental concerns associated with conventional methods, researchers are on a continuous hunt to find clean alternatives in order to manage weeds. Fungi have shown promising weedicide potential in lab studies. The current study aimed to isolate endophytic fungi from wheat plants which can promote wheat growth and inhibit the growth of common weed, A. fatua. Of several isolates, GW (grayish white) was selected for its promising features, and the strain was identified as Fusarium oxisporum through ITS sequencing technique. This fungus released a number of compounds including Isovitexin, Calycosin, quercetagetin, and dihydroxy-dimethoxyisoflavone that inhibited the growth of A. fatua but did not influence the growth of wheat seedlings. Biomass of this fungus in the soil also reduced growth parameters of the weed and promoted the growth of wheat. For instance, the vigor index of A. fatua seedlings was reduced to only 6% of the control by this endophyte. In contrast, endophyte-associated wheat seedlings showed a higher vigor index than the control. Behind this differential response of the two plants were their contrasting physiological and biochemical status. Lower growth phenotypes of A. fatua seedlings had reduced levels of IAA, GAs, and SA and higher the levels of JA and ABA. Besides, their ROS scavenging ability was also compromised as evident from relatively lower activities of catalase, peroxidase, and ascorbic acid oxidase, as well as higher accumulation of ROS in their leaves. Wheat seedlings response to GW was opposite to the A. fatua. It may be concluded that F. oxysporum GW has the ability to differentially modulate physiology and biochemistry of the two hosts leading to contrasting phenotypic responses.

Microbial production of plant hormones: Opportunities and challenges

Plant hormones are a class of organic substances which are synthesized during the plant metabolism. They have obvious physiological effect on plant growth at very low concentrations. Generally, plant hormones are mainly divided into 5 categories: auxins, cytokinins, ethylene, gibberellins (GAs) and abscisic acid (ABA). With the deepening of research, some novel plant hormones such as brassinosteroid and salicylates have been found and identified. The plant hormone products are mainly obtained through plant extraction, chemical synthesis as well as microbial fermentation. However, the extremely low yield in plants and relatively complex chemical structure limit the development of the former 2 approaches. Therefore, more attention has been paid into the microbial fermentative production. In this commentary, the developments and technological achievements of the 2 important plant hormones (GAs and ABA) have been discussed. The discovery, producing strains, fermentation technologies, and their accumulation mechanisms are first introduced. Furthermore, progresses in the industrial mass scale production are discussed. Finally, guidelines for future studies for GAs and ABA production are proposed in light of the current progress, challenges and trends in the field. With the widespread use of plant hormones in agriculture, we believe that the microbial production of plant hormones will have a bright future.

Production of bikaverin by a Fusarium fujikuroi mutant in submerged cultures

A variety of mutants having different colony characteristics, morphology and soluble pigmentation were generated from Fusarium fujikuroi by exposure to UV radiation. Mutants were selected that formed dry, compact, small colonies with reddish-violet pigment on regeneration agar plates. The production of bikaverin by Mut-4 was examined in shake flasks in media with different nitrogen and carbon sources. The optimal C: N ratio for the maximal bikaverin production by Mut-4 was 150:1. It produced still higher bikaverin (6.3 g l(-1)) in a medium containing defatted cottonseed meal as nitrogen source, in combination with glucose. Bikaverin produced was extracted, purified and characterized by UV-visible and NMR spectroscopy. Bikaverin production in the present investigation was substantially higher than that reported by earlier investigators in submerged and solid-state fermentations.

Enhanced production of gibberellin A4 (GA4) by a mutant of Gibberella fujikuroi in wheat gluten medium

Mutants of Gibberella fujikuroi with different colony characteristics, morphology and pigmentation were generated by exposure to UV radiation. A mutant, Mor-189, was selected based on its short filament length, relatively high gibberellin A(4) (GA(4)) and gibberellin A(3) (GA(3)) production, as well as its lack of pigmentation. Production of GA(4) by Mor-189 was studied using different inorganic and organic nitrogen sources, carbon sources and by maintaining the pH of the fermentation medium using calcium carbonate. Analysis of GA(4) and GA(3) was done by reversed-phase high-performance liquid chromatography and LC-MS. The mutants of G. fujikuroi produced more GA(4) when the pH of the medium was maintained above 5. During shake flask studies, the mutant Mor-189 produced 210 mg l(-1) GA(4) in media containing wheat gluten as the nitrogen source and glucose as the carbon source. Fed-batch fermentation in a 14 l agitated fermenter was performed to evaluate the applicability of the mutant Mor-189 for the production of GA(4). In 7-day fed-batch fermentation, 600 mg l(-1) GA(4) were obtained in the culture filtrate. The concentration of GA(4) and GA(3) combined was 713 mg l(-1), of which GA(4) accounted for 84% of the total gibberellin. These values are substantially higher than those published previously. The present study indicated that, along with maintenance of pH and controlled glucose feeding, the use of wheat gluten as the sole nitrogen source considerably enhances GA(4) production by the mutant Mor-189.