Evolutionary engineering of Fusarium fujikuroi for enhanced production of gibberellic acid

Abstract

Fusarium fujikuroi is the microorganism that used for industrial production of gibberellic acids (GAs), a commercially very important plant hormone. A stable, high-yielding F. fujikuroi strain is essential for efficient bio-production. Although, there is a quick development in molecular tools and metabolic engineering research for this microbe in the past decade, the current industrially applying strains are mostly obtained from numerous rounds of mutagenesis and screening, while the industry is still dedicating in strain improvement work based mostly on this method. However, after over half a century’s effort, the yield is still maintained at a low level today. We designed an efficient strategy for strain improvement by amphotericin B resistance prescreening and evolutionary engineering. A superior strain was obtained with over 25% increased yield after testing merely 640 isolates. The superior strain was later confirmed to be genetically very stable for GA production. Minimum inhibitory concentration (MIC) assay verified its increased resistance to amphotericin B, whose target ergosterol shares a same precursor with GAs. Decreased ergosterol accumulation indicated the increased GA3 synthesis accompanied with attenuation of metabolic branch flux. In the end, we found the increased GA3 titer of the superior strain also accompanied with faster growing biomass.