O-024. The Gα1 Protein Regulates Aspergillus niger Growth and Development and the Citric Acid Production in Response to Nitrogen Sources
In this study we examined the regulation of G protein alpha (Gα1, Gα2, Gα3) and gamma (Gγ) subunits on the vegetative growth and morphological formation and the citric acid production of Aspergillus niger (ATCC11414) under different culture conditions via gene deletion. The RNA gel-blotting analysis showed that the transcription of all four genes was much higher during the filamentous growth than the pelleted growth. The Gα1 deletion severely suppressed A. niger growth in complete medium, while the deletion of Gα2, Gα3 and Gγ did not affect its growth in the same medium. The growth of the Gα1 deletion mutants was also affected in minimum medium, but less significant than that in the CM medium. Furthermore, we measured the 15NH4 uptake and utilization of the Gα1 mutants in citric acid production (CAP) medium, where ammonium nitrate was substituted with alanine or aspartic acid, and found that the Gα1 deletion mutant had higher rate of 15NH4 uptake and utilization than the parent strain. Grown in the CAP medium with different selected amino acid as nitrogen source, the Gα1 mutant growth was pH-dependent. The Gα1 deletion mutants grown on CAP medium plate exhibited some filamentous growth, while other deletion mutants and the parent strain maintained the pelleted growth. Similarly, the Gα1 deletion mutants had much lower citric acid production and biomass accumulation in the CAP culture medium, while other deletion mutants had similar levels to the parent strain. These results suggest that the Gα1 may function in regulating the vegetative growth, morphological formation and the citric acid production of A. niger as a response to changes in nitrogen sources.