. The ?rst step in conidiophore development is the activation of the transcriptional regulator BrlA, which induces the expression of a number of conidiation speci?c genes. BrlA expression table 5 is autoregulated, resulting in a strong accumulation of its mRNA during asexual development. Although most conidiation studies are performed at a substrate air interface, conidiation can also be induced in submerged cultures by nutrient limita tion such as severe carbon limitation. Under these conditions, carbon from endogenous resources becomes mobilized to fuel maintenance and self propagation. Con sequently, the fungal mycelium becomes highly hetero geneous, bearing empty compartments and those that are committed to conidiation.

While this strategy is bene?cial for self propagation and the exploitation of new substrate sources during saprophytic growth, it may result in a decrease of the active biomass fraction during carbon limited industrial production processes. Only a few studies have been conducted to investigate di?erent aspects of aging carbon limited fungal cultures. As discussed in the review by White et al. most of them focus on physiological and morphological aspects. The generic term autolysis has been frequently used to summarize the involved processes. Hallmarks of autol ysis are biomass decline, hyphal fragmentation, release of ammonia and increased extracellular hydrolase activ ity. For di?erent fungal species, the involvement of hydrolases, especially chitinases and glucanases but also proteases has been investigated in great detail.

An early and strong transcriptional induction in response to carbon starvation was shown in A. nidualns for the two hydrolases ChiB and NagA, which have been intensively studied because of their role in the degradation of the cell wall component chitin. In addition to physiolog ical and biochemical hallmarks of aging fungal cultures, several approaches have been developed to quantify the decreasing fraction of active hyphal compartments in aging mycelium by automated image analysis. An increasing number of publications highlights the importance of programmed cell death in aging fun gal cultures. PCD is generally classi?ed into three types, which are referred to as apoptosis, autophagy and necrosis. Their physiological roles are very complex and their relation ships are not completely understood.

While apoptosis and necrosis are explicitly associated with cell death, autophagy is also a normal physiological process impor tant for cellular homeostasis by lysosomal degradation and recycling. The cellular Brefeldin_A functions of autophagy have been proposed to exert roles that are both selleck chemicals Tipifarnib causative of and protective against cell death. Improving our understanding of processes induced by carbon starvation and their dynamic interactions is important to further optimize industrial production pro cesses. The aim of this study is to provide a system wide description of the carbon starvation response of the ?lamentous fungus A. niger. S