Flavonoids are crucial in physiological and pharmaceutical processes, especially the treatment of cancer and the prevention of cardiovascular and cerebrovascular diseases. Flavonoid-producing plants and fungi have been extensively reported, but bacteria have been much less investigated as a source of flavonoid production. Deinococcus sp. 43, a spherical flavonoid-producing bacteria from the Ginkgo rhizosphere, was reported in this study. First, the whole genome of Deinococcus sp. 43 was sequenced and a series of flavonoid anabolic genes were annotated. Simultaneously, High Performance Liquid Chromatography (HPLC) results showed that Deinococcus sp. 43 was capable of producing flavonoids, with a maximum quercetin output of 2.9 mg/L. Moreover, the relative expression of key genes involved in flavonoid synthesis was determined to test the completeness of the flavonoid anabolic pathway. The results of LC-MS analysis demonstrated that the flavonoids produced by Deinococcus sp. 43 were significantly different between intracellular and extracellular environments. The concentration of multiple glycosylated flavonoids was substantially higher in extracellular than intracellular environments, while the majority of flavonoids obtained in intracellular environments were hydroxylated multiple times. Lastly, the flavonoid biosynthetic pathway of Deinococcus sp. 43 was constructed based on the genomic analysis and the detected flavonoids. In conclusion, this study represents the first comprehensive characterization of the flavonoid-producing pathway of Deinococcus. The findings demonstrate that the strain has excellent potential as a genetically engineered strain for the industrial production of flavonoids.

Aspergillus fijiensis is an industrially important filamentous fungus, whose genetic analysis has been limited by the absence of species-specific tools. This study establishes an optimized CRISPR–Cas9 genome editing platform for A. fijiensis, from protoplast preparation to DNA repair pathway engineering. Antibiotic screening first identified hygromycin B and 5-FOA (5-fluoroorotic acid) as effective positive and counter-selection markers. A high-efficiency protoplast regeneration protocol was developed depending on specific osmotic stabilization and mycelial competence. Evaluation of a plasmid-based CRISPR system revealed that while autonomous replication was feasible, gene editing was constrained by low efficiency and a predominant bias toward NHEJ (non-homologous end joining). We implemented a Cas9–sgRNA RNP (ribonucleoprotein) delivery approach, with RNP delivery alone producing frequent indels. However, targeted integration remained inefficient when using conventional MMEJ (Microhomology-mediated end joining) donors. By employing donors containing short (5 bp) microhomology arms between cleavage sites, we effectively engaged the MMEJ pathway, enabling precise insertions and large-fragment deletions in 92% of the analyzed transformants. Donor templates containing minimal 5 bp microhomology sequences could effectively shift the predominant repair pathway from NHEJ to MMEJ. These findings demonstrate that MMEJ is the superior pathway with a unique mechanism for genome engineering in A. fijiensis, providing a versatile toolkit for unlocking the biotechnological potential of this recalcitrant species and a successful paradigm for establishing genetic systems in other species.