Process development of oxalic acid production in submerged culture of Aspergillus niger F22 and its biocontrol efficacy against the root-knot nematode Meloidogyne incognita.

Abstract

Oxalic acid has potent nematicidal activity against the root-knot nematode Meloidogyne incognita. In this study, fermentation parameters for oxalic acid production in submerged culture of Aspergillus niger F22 at 23, 25, and 30°C were optimized in 5-L jar fermenters. The viscosity of the culture broth increased with increasing temperature. There was a negative correlation between oxalic acid production and the apparent viscosity; high volumetric productivity of oxalic acid was obtained at low apparent viscosity (less than 1000cP), with a productivity of more than 100mg/L h. When the apparent viscosity was over 2500cP, the volumetric productivity decreased below 50mg/L h. In addition, the volumetric mass transfer coefficient, K L a, positively correlated with volumetric productivity. When the K L a value increased from 0.0 to 0.017/s, the volumetric productivity proportionally increased up to 176mg/L h. When the temperature decreased, K L a increased due to the decrease in viscosity, leading to increased volumetric productivity. The highest productivity of 7453.3mg/L was obtained at the lowest temperature, i.e., 23°C. The nematicidal activity of culture filtrate was proportional to the content of oxalic acid. Based on a constant impeller tip speed, oxalic acid production was successfully scaled up to a 500-L pilot vessel, producing a final concentration comparable to that in the 5-L jar.