Nitrification of aspartate by Aspergillus flavus

Area of Science:

• Microbiology
• Biochemistry

Background:

• Microbial nitrification is crucial for nitrogen cycling.
• Fungi, like Aspergillus flavus, can heterotrophically convert amino acids to nitrogenous compounds.

Purpose of the Study:

• To investigate the heterotrophic nitrification of l-aspartic acid by Aspergillus flavus.
• To identify the optimal amino acid sources for nitrate production and explore metabolic pathways.

Main Methods:

• Utilized a replacement incubation system with Aspergillus flavus.
• Employed uniformly labeled (14)C-l-aspartate to trace metabolic fate.
• Analyzed culture filtrates and mycelial components for nitrification products and intermediates.

Main Results:

• l-Aspartic acid and glutamate were the most effective amino acid sources for nitrate production.
• Bicarbonate addition enhanced nitrification for most amino acids, but not aspartic acid.
• No direct correlation was found between nitrate formation and common nitrification intermediates.
• (14)C-l-aspartate was incorporated into fungal biomass, particularly glucosamine and acetylglucosamine, with label redistribution to other amino acids.

Conclusions:

• Aspergillus flavus efficiently converts l-aspartic acid to nitrate through a heterotrophic nitrification pathway.
• The metabolic fate of aspartate involves its incorporation into fungal cell wall components rather than direct conversion to extracellular nitrification products.
• Further research is needed to elucidate the obscure bicarbonate effect on nitrification.