Polyol synthesis inAspergillus niger: Influence of oxygen availability, carbon and nitrogen sources on the metabolism

Abstract

Polyol production has been studied in Aspergillus niger under different conditions. Fermentations have been run using high concentration of glucose or xylose as carbon source and ammonium or nitrate as nitrogen source. The growth of biomass, as freely dispersed hyphae, led to an increase of medium viscosity and hereby a decrease in mass transfer, especially oxygen transfer. The consequence was a decrease in DOT and the occurrence of a switch between fully aerobic conditions and oxygen-limited conditions. Metabolite quantification showed that polyols were the main metabolic products formed and represented up to 22% of the carbon consumed in oxygen-limited conditions. The polyol concentration and the polyol pattern depended strongly on the environmental conditions. This is due to a complex regulation of polyol production and to the fact that each polyol can fulfill different functions. In this study, erythritol, xylitol, and arabitol were produced as carbon storage compounds when the flux through the PP pathway exceeded the need in ribulose-5-phosphate for the biomass synthesis. Glycerol, erythritol, and xylitol seem to be involved in osmoregulation. Mannitol was produced when the catabolic reduction of charge was high. Its production involves the enzyme NAD-dependent mannitol-1-phosphate dehydrogenase and seems to be the main cytosolic route for the NADH reoxidation during oxygen limitation.

Osmotic adaptation of the halophilic fungus Hortaea werneckii: role of osmolytes and melanization

“…All four polyols have been detected in some Aspergillus species (Beever & Laracy, 1986;Nesci et al, 2004) and in C. sake (Abadias et al, 2000). In addition to their use as compatible solutes, polyols can also serve as carbon storage compounds, they may help in balancing the cellular redox potential (Diano et al, 2006), and they can act as scavengers of reactive oxygen species (Voegele et al, 2005). At optimal growth salinity, H. werneckii accumulated a mix of polyols with different lengths of carbon backbone (from three to six atoms) in various ratios.…”

Effect of controlled oxygen limitation on Candida shehatae physiology for ethanol production from xylose and glucose

“…According to previous studies [8], polyols are involved in carbohydrate storage, in microbial response to osmotic pressure, translocatory compounds and redox sink.…”

Optimization of biomass production with enhanced glucan and dietary fibres content by Pleurotus ostreatus ATHUM 4438 under submerged culture

“…Polyols may play a role in balancing the cellular redox potential as the synthesis and catabolism of polyols generally involve the cofactors NADH and NADPH. In the particular case of mannitol, the enzymes present could allow the interconversion of fructose-6-phosphate and mannitol [33,34]. This interconversion, known as the mannitol cycle would lead to generation of NADPH using NADH and ATP.…”