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The fungal strain Humicola lutea 103 was used as a model organism to examine the relationship between copper toxicity and oxidative stress in low eukaryotes such as filamentous fungi. Spores or submerged cultures were treated with different copper concentrations and the oxidative stress-inducing agent paraquat (PQ). Oxidative stress biomarkers such as reactive oxygen species (ROS), cyanide-resistant respiration, protein carbonyls, reserve carbohydrates, and antioxidant defence were identified in cells treated or not treated with either copper ions or PQ. Copper inhibited the growth and conidiospore formation of H. lutea 103 in a concentration-dependent manner. This treatment also resulted in increased superoxide anion radical formation. Copper stress was furthermore accompanied by transient accumulation of trehalose and glycogen, as well as increased protein carbonyl content. Compared to control cultures, copper-treated mycelia demonstrated a marked increase in the activity of protective enzymes (superoxide dismutase, catalase, and glucose-6-phosphate dehydrogenase). These increased antioxidant enzyme activities were blocked by inhibitors of protein synthesis, suggesting that de novo enzyme formation was involved. Biomarker response to the heavy metal was similar to treatment with known ROS generators such as PQ. The observed hyper-oxidative status and increased oxidative damage suggest a relationship between acute metal treatment and oxidative stress in fungal cells.

Conidia of Aspergillus niger 26 spores were immobilised in 3% Ca-alginate beads and some intrinsic kinetic characteristics including growth, polymethylgalacturonase (PMG) production and specific oxygen uptake rates determined. A negative correlation between the specific growth rate and specific PMG production indicated a non-growth-associated enzyme formation. Immobilisation did not change the model of PMG synthesis even in repeated replacement cultures and leads under certain conditions to an enhanced PMG production. The immobilised mycelium was concentrated at the surface layer of the alginate beads and the fungal hyphae could not be found in the central part of the gel. The dense growth of the mycelia on the outer bead surface allowed the formation of a fur-like mycelium coat, which had a large surface for oxygen uptake. This growth behaviour is a reason why the effectiveness factor increased during incubation from 0.54 to 0.93.

Humicola lutea 120-5 spores were immobilized in a mixed photo-crosslinked polyvinyl alcohol and calcium-alginate gel. Maximum enzyme synthesis was established with 1:8 (v:v) gel beads: growth medium inoculum and 48 h duration of one cycle. The free cells were very unstable in replacement fermentations. The operational stability of the immobilized system indicated the possibility of the application of Humicola lutea 120-5 in a semi-continuous process for the production of acid proteinase.

Spores of Aspergillus niger 26 were immobilised in calcium alginate and the immobilised growing mycelium reused in batch mode for the production of polymethylgalacturonase (PMG). The influence of alginate concentration, initial inoculum gel volume, spore concentration, and duration of the fermentation cycle on enzyme activity and mycelium growth are reported. The best yield of PMG was reached with 5 ml initial gel volume 3% alginate concentration, 109 spores/ml gel and a cycle time of 72 h. The optimisation of these factors, which affect the stability and productivity of the immobilised system, resulted in an increase in enxyme activity and the possibility of semicontinuous cultivation.