Regulation of Autolysis in Aspergillus nidulans

Abstract

In terms of cell physiology, autolysis is the centerpiece of carbon-starving fungal cultures. In the filamentous fungus model organism Aspergillus nidulans, the last step of carbon-starvation-triggered autolysis was the degradation of the cell wall of empty hyphae, and this process was independent of concomitantly progressing cell death at the level of regulation. Autolysis-related proteinase and chitinase activities were induced via FluG signaling, which initiates sporulation and inhibits vegetative growth in surface cultures of A. nidulans. Extracellular hydrolase production was also subjected to carbon repression, which was only partly dependent on CreA, the main carbon catabolite repressor in this fungus. These data support the view that one of the main functions of autolysis is supplying nutrients for sporulation, when no other sources of nutrients are available. The divergent regulation of cell death and cell wall degradation provides the fungus with the option to keep dead hyphae intact to help surviving cells to absorb biomaterials from dead neighboring cells before these are released into the extracellular space. The industrial significance of these observations is also discussed in this paper.

MeaB-dependent nutrition sensing regulates autolysis in carbon starved Aspergillus nidulans cultures

“…1). Addition of 4 g/l yeast extract to the medium hindered both DCM declination and extracellular chitinase production (extracellular chitinase activity factored with DCM), which is a good marker of autolytic cell wall degradation [4], was also higher in minimal medium than those found in yeast-extract-supplemented nutrient-rich medium (Fig. 1).…”

“…In previous experiments, we studied the glucose-mediated repression of autolysis in A. nidulans. We found that glucose repressed the autolytic cell wall degradation via the carbon catabolite repressor CreA as well as independently of CreA, via repressing the conidiogenesis regulatory gene brlA and activating the heterotrimeric G protein FadA-dependent signalling [4, 8].Here, we studied the effect of yeast extract on the autolysis of A. nidulans. We demonstrated that the bZip-type transcription factor MeaB, an activator of nmrA expression and a co-repressor of areA expression [9], was involved in the yeast-extract-mediated repression of autolytic cell wall degradation.…”

“…Autolysis regulated process, which helps these microorganisms to survive in a continuously changing, hostile environment [2][3][4]. Emerging regulatory elements of autolysis provide us with promising tools to control and manipulate this process for several practical purposes in the fermentation industry [2,4]. Moreover, a deeper understanding of the underlying mechanism of fungal autolysis may also be exploited in future antifungal drug research [5][6][7].…”

“…In previous experiments, we studied the glucose-mediated repression of autolysis in A. nidulans. We found that glucose repressed the autolytic cell wall degradation via the carbon catabolite repressor CreA as well as independently of CreA, via repressing the conidiogenesis regulatory gene brlA and activating the heterotrimeric G protein FadA-dependent signalling [4, 8].…”

“…Aspergillus nidulans, the last step of carbon starvation triggered autolysis is the degradation of the cell wall of empty hyphae (autolytic cell wall degradation). The regulation of this process is independent of concomitantly progressing cell death [4]. In previous experiments, we studied the glucose-mediated repression of autolysis in A. nidulans.…”