Disordered ultrastructure in lignin-peroxidase-secreting hyphae of the white-rot fungus Phanerochaete chrysosporium

Abstract

The practice of exposing liquid cultures of the white-rot fungus Phanerochaete chrysosporium to a pure oxygen atmosphere under conditions of nutrient starvation has been widely adopted to induce lignin peroxidase (LiP) synthesis. Transmission electron microscopy was used to examine hyphal cells of carbonlimited cultures that had been exposed to an atmosphere of pure oxygen, and revealed evidence of a major loss in organization of cellular ultrastructure, which may be attributed to oxygen toxicity. Under some conditions (continuous agitation in air with cellulose as the carbon source) cultures will produce LiP without needing to be exposed to a pure oxygen atmosphere. A similar major loss of cellular ultrastructure was found in hyphal cells from such cultures upon examination. Investigation of the levels of H 2 O 2 , catalase and carbonyl content of intracellular proteins suggests that the latter cultures developed a hyperoxidant state because the rate of supply of carbon from cellulose hydrolysis was insufficient for oxygen homeostasis. The association of LiP with these cultures and with those exposed to an atmosphere of pure oxygen infers that LiP may be triggered in response to oxidant stress.

In situ localization of manganese peroxidase production in mycelial pellets of Phanerochaete chrysosporium

“…Fragmentation of idiophasic fungal hyphae is under metabolic and environmental control (Gow, 1994) and may result in differentiated cell structures having particular metabolic properties: for example yeast-like cells synthesizing the antibiotic cephalosporin in Acremonium chrysogenum (Bartoshevich et al, 1990;Sandor et al, 1998). In the case of P. chrysosporium it has been reported that a hyperoxidant state of growth, caused by limiting respirable carbon, induces a disorganization in the intracellular architecture of LiP-secreting hyphae in mycelial pellets, which in turn may promote enzyme production (Zacchi et al, 2000). Production of metabolically active chlamydospore-like cells by P. chrysosporium might therefore result from a particular physiological context in the MnP-producing pellet medium.…”

Understanding LiP Promoters from Phanerochaete chrysosporium: A Bioinformatic Analysis

“…Under LiP producing conditions, hyphal cells undergo a major loss of cellular ultrastructure, similar to that observed under oxidative stress (Zacchi et al, 2000). Therefore LiPs may be enzymes that are induced under conditions of oxidative stress (Rabinovich et al, 2004) and degrade lignin in order to access further carbon sources (Zacchi et al, 2000). Taken together, many of the genes shown to contain any of these motifs have in common that they regulate genes of relevance associated to the biological processes that occur during lignin biodegradation.…”

“…Networks of spherical and tubular vacuoles have been found in a range of filamentous fungi, including the wood rotting plant pathogen Phanerochaete velutina (Richards et al, 2010). Under LiP producing conditions, hyphal cells undergo a major loss of cellular ultrastructure, similar to that observed under oxidative stress (Zacchi et al, 2000). Therefore LiPs may be enzymes that are induced under conditions of oxidative stress (Rabinovich et al, 2004) and degrade lignin in order to access further carbon sources (Zacchi et al, 2000).…”

“…During secretion of enzymes involved in the ligninolytic process, such as LiPs and MnPs, oxidative stress is a natural condition of P. chrysosporium and resistance to oxidative stress is probably an important function (Zacchi et al, 2000;Belinky et al, 2003;Jiang et al, 2005). To date there is no clear evidence in the literature on the mechanisms used by P. chrysosporium to tolerate the highly oxidative environment produced during lignin degradation.…”

“…wood (Weber, 2002). Fungal cells within a single mycelium are known to autolyse to provide nutrients to ensure growth (Zacchi et al, 2000), involving processes related to the remodeling of the mycelium. In fungi, vacuoles are very versatile organelles involved in protein turnover, cellular homeostasis, membrane trafficking, signaling and nutrition (Veses et al, 2008), as well as progression through cell cycle checkpoints (Richards et al, 2010).…”