Mycelial pellet formation by edible ascomycete filamentous fungi, Neurospora intermedia

Abstract

Pellet formation of filamentous fungi in submerged culture is an imperative topic of fermentation research. In this study, we report for the first time the growth of filamentous ascomycete fungus, Neurospora intermedia in its mycelial pellet form. In submerged culture, the growth morphology of the fungus was successfully manipulated into growing as pellets by modifying various cultivation conditions. Factors such as pH (2.0–10.0), agitation rate (100–150 rpm), carbon source (glucose, arabinose, sucrose, and galactose), the presence of additive agents (glycerol and calcium chloride) and trace metals were investigated for their effect on the pellet formation. Of the various factors screened, uniform pellets were formed only at pH range 3.0–4.0, signifying it as the most influential factor for N. intermedia pellet formation. The average pellet size ranged from 2.38 ± 0.12 to 2.86 ± 0.38 mm. The pellet formation remained unaffected by the inoculum type used and its size showed an inverse correlation with the agitation rate of the culture. Efficient glucose utilization was observed with fungal pellets, as opposed to the freely suspended mycelium, proving its viability for fast-fermentation processes. Scale up of the pelletization process was also carried out in bench-scale airlift and bubble column reactors (4.5 L).

Does the second messenger cAMP have a more complex role in controlling filamentous fungal morphology and metabolite production?

“…() suggested that carbon sources such as glucose repression might be largely dependent on the cAMP signaling pathway, which in turn represses the production of secondary metabolites in Monascus . Mapari, Meyer, and Thrane () valuated morphology and yellow pigment production in Epicoccum nigrum and demonstrated that the growth‐type in form of pellet favored the production of yellow pigments, an observation that coincides with our research findings regarding ethanol production and pigmentation in N. intermedia (Méndez, Pérez, Montañéz, Martínez, & Aguilar, ; Nair et al., ). However, the influence of the levels of cAMP on fungal morphology such as mycelial pellets is yet to be investigated in detail and little is known about the amalgamated link between fungal morphological responses and the metabolite production, in relation to the factors affecting the cAMP levels in filamentous fungi.…”

“…Exploring its ability to grow rapidly on various types of industrial waste streams, N. intermedia could become a core biocatalyst in any biorefinery approach with its potential to produce an array of products (Gmoser, Ferreira, Lennartsson, & Taherzadeh, ). For the first time, our group has recently manipulated N. intermedia to grow as mycelial pellets (Nair, Lennartsson, & Taherzadeh, ), thereby enabling it to adopt diverse morphologies when cultivated in submerged cultures, such as the uniform and long filaments or entangled filaments in pellets or clumps. Filamentous fungal morphology has been reported to greatly influence the secretion of several metabolites and products (Choudhari, Ananthanarayan, & Singhal, ; Torres et al., ).…”

The filamentous fungal pellet—relationship between morphology and productivity

“…Filamentous growth was observed at higher pH (8–9). The growth of ascomycete fungus Neurospora intermedia in uniform pellet form can be achieved using a pH range of 3.0–4.0 (Nair et al 2016 ).…”

Novel self‐immobilized biomass mixture based on mycelium pellets for wastewater treatment: A review

“…The growth and morphology of the pellets depend on four main factors, namely the genetic materials, the inoculum concentration, medium components, and the physical conditions such as temperature, pH, mechanical forces, and the conditions of the culture. The pH range of 3.0–5.0, together with saccharose and glucose, and ammonium chloride as carbon and nitrogen sources, respectively, is beneficial to the growth of the pellets along with the inoculum concentration of 10 4 spores/ml, the temperature range of 25–37°C, and the agitation rate of 100–150 rpm (Nair, Lennartsson, & Taherzadeh, ). Further, the pellet production in several strains of filamentous fungi would be restrained with the growth of the pellets.…”

“…The following four mechanisms have been identified for the removal of pollutants in water by pellets: (a) Porous structure—The porous structure of pellets provides an increased adsorption capacity for heavy metals and other macromolecules such as dye molecules (Baldrian, ; Espinosa‐Ortiz, Rene, et al., ; Nair et al., ), (b) EPS—Fungi can produce EPS with functional groups, which offer binding sites for adsorbing other substances and pollutants, (c) Self‐growth—Since active fungi can grow and reproduce, it can reduce the cost and time to produce the biomass. Additionally, the by‐products are eco‐friendly compared to other materials (Bosso et al., ; Zhang et al., ), (d) Organic degradation capacity and self‐immobilization—Some mycelial fungi can degrade organic pollutants using the cell enzymes or extracellular polymeric substances.…”