Comparative genomics of the aconidial Aspergillus niger strain LDM3 predicts genes associated with its high protein secretion capacity.

Aspergillus niger is widely used as a cell factory for homologous and heterologous protein production. As previous studies reported that reduced sporulation favors protein secretion in A. niger, in this study, we conducted a comparative genomic analysis of the non-sporulating industrially exploited A. niger strain LDM3 in China and the reference protein secretion strain CBS 513.88 to predict the key genes that might define the genetic basis of LDM3's high protein-producing potential in silico. After sequencing using a hybrid approach combining Illumina and PacBio sequencing platforms, a high-quality genome sequence of LDM3 was obtained which harbors 11,209 open reading frames (ORFs). LDM3 exhibits large chromosomal rearrangements in comparison to CBS 513.88. An alignment of the two genome sequences revealed that the majority of the 457 ORFs uniquely present in LDM3 possessed predicted functions in redox pathways, protein transport, and protein modification processes. In addition, bioinformatic analyses revealed the presence of 656 ORFs in LDM3 with non-synonymous mutations encoding for proteins related to protein translation, protein modification, protein secretion, metabolism, and energy production. We studied the impact of two of these on protein production in the established lab strain N402. Both tupA and prpA genes were selected because available literature suggested their involvement in asexual sporulation of A. niger. Our co-expression network analysis supportively predicted the role of tupA in protein secretion and the role of prpA in energy generation, respectively. By knockout experiments, we showed that the ΔtupA mutant displayed reduced sporulation (35%) accompanied by higher total protein secretion (65%) compared to its parental strain. Such an effect was, however, not observed in the ΔprpA mutant.