Detection of metabolic activity in dormant conidia of Aspergillus niger and use of growth inhibitors to study transient developmental changes.. Aspergillus niger

The early stages of development of Aspergillus niger conidia during outgrowth were explored by combining genome-wide gene expression analysis (RNAseq), proteomics, Warburg manometry and uptake studies. Resting conidia were shown to be metabolically active as low levels of oxygen uptake and the generation of carbon dioxide were detected, suggesting that low-level respiratory metabolism occurs in conidia for maintenance. Upon triggering of spore germination, generation of CO2 started immediately. For a short period, which coincided with mobilisation of the intracellular polyol, trehalose, there was no increase in uptake of O2 indicating that trehalose was metabolised by fermentation. Data from genome-wide mRNA profiling showed the presence of transcripts associated with fermentative and respiratory metabolism in resting conidia. Following triggering of conidial outgrowth, there was a clear switch to respiration after 25 min, confirmed by cyanide inhibition. No effect of SHAM on respiration suggests electron flow via cytochrome c oxidase. Glucose entry into spores was not detectable before 1 h after triggering germination. Sub-inhibitory levels of sorbic acid delayed both the turnover of trehalose and the uptake of glucose. Oxygen uptake was also then inhibited, delaying the onset of respiration and extending the period of fermentation. Overall design: Duplicate samples from each time point: dormant conidia MN_T0 (MN_T0A + MN_T0B), conidia germinated for one hour MN_T1 (T1 MN_T1A + MN_T1B) and conidia germinated for one hour in the presence of 1mM of sorbic acid MN_T1SA (MN_T1SA_A + MN_T1SA_B)