Optimization of protoplast based DNA isolation and genome analysis in a gamma-irradiated Aspergillus niger mutant strain.

Aspergillus niger is an important industrial fungus widely used for citric acid production and a range of biotechnological applications. In this study, a protoplast-based DNA isolation protocol was optimized for a gamma-irradiated A. niger AN-L103_M1 mutant strain, followed by whole-genome sequencing and functional genome analysis. Protoplast yield was strongly influenced by enzyme concentration and the molarity of the osmotic stabilizer. The highest yield was achieved at an enzyme concentration of 50 mg/mL (2.487 ± 0.04 × 10⁸ cells/mL) and 0.8 M KCl (2.550 ± 0.06 × 10⁸ cells/mL), with both factors showing significant effects (p < 0.0001) in GraphPad Prism 11.0.0. Whole-genome sequencing performed using an Illumina NovaSeq 6000 platform yielded a 37.06 Mb draft genome assembled into 537 contigs, with an N50 of 363,084 bp and a GC content of 48.2%. BUSCO 14 analysis showed high completeness (97.95% complete BUSCOs). Functional annotation and KEGG pathway mapping identified genes involved in glycolysis, the tricarboxylic acid cycle, and citrate biosynthesis, while biosynthetic gene cluster analysis revealed diverse potential for secondary metabolite production. These findings provide an optimized workflow for protoplast-based DNA isolation and genome-scale functional analysis in A. niger, proposing a basis for future comparative genomics, transformation studies, and experimentally validated metabolic engineering.