Effect of culture conditions and induction strategies on production of human interleukin-6 by a recombinant Aspergillus nidulans strain

Future insights in fungal metabolic engineering

Filamentous fungi exhibit versatile abilities, including organic acid fermentation, protein production, and secondary metabolism, amongst others, and thus have applications in the medical and food industries. Previous genomic analyses of several filamentous fungi revealed their further potential as host microorganisms for bioproduction. Recent advancements in molecular genetics, marker recycling, and genome editing could be used to alter transformation and metabolism, based on optimized design carbolated with computer science. In this review, we detail the current applications of filamentous fungi and describe modern molecular genetic tools that could be used to expand the role of these microorganisms in bioproduction. The present review shed light on the possibility of filamentous fungi as host microorganisms in the field of bioproduction in the future.

Biopharmaceuticals from microorganisms: from production to purification

The use of biopharmaceuticals dates from the 19th century and within 5–10 years, up to 50% of all drugs in development will be biopharmaceuticals. In the 1980s, the biopharmaceutical industry experienced a significant growth in the production and approval of recombinant proteins such as interferons (IFN α, β, and γ) and growth hormones. The production of biopharmaceuticals, known as bioprocess, involves a wide range of techniques. In this review, we discuss the technology involved in the bioprocess and describe the available strategies and main advances in microbial fermentation and purification process to obtain biopharmaceuticals.

Induction of hexanol dehydrogenase in Geotrichum spp. by the addition of hexanol

Excessive hexanol content distorts the flavor of foods and is harmful to human health. Previously, two strains of fungi were found capable of producing hexanol-degrading enzymes. The current study identified these strains as Galactomyces geotrichum according to the gene sequence of the 26 S rDNA D1/D2 region (strain S12) and genus Geotrichum according to the gene sequence of ITS region (strain S13). Parallel analysis of extracellular and intracellular enzyme activities showed that the enzymes mainly accumulated intracellularly. Native polyacrylamide gel electrophoresis with reactive dyes showed the enzymes were alcohol dehydrogenases induced by the addition of hexanol. Hexanol was catalyzed into hexanoic acid and hexanal by strain S12 and into hexanoic acid by strain S13. The optimum conditions for the induction of enzymes were determined to be 6-9 h in the presence of 0.7 g/l hexanol. The identification of two strains capable of enzymatically degrading hexanol and optimum conditions for their induction will facilitate their use in industrial applications.

Chymostatin can combine with pepstatin to eliminate extracellular protease activity in cultures of Aspergillus niger NRRL-3

Aspergillus strains are being considered as potential hosts for recombinant heterologous protein production because of their excellent extracellular enzyme production characteristics. However, Aspergillus proteases are problematic in that they modify and degrade the heterologous proteins in the extracellular medium. In previous studies we observed that media adjustments and maintenance of a filamentous morphology greatly reduced protease activity and that a low concentration of the aspartic protease inhibitor pepstatin inhibited the latter protease activity to the extent of approximately 90%. In this paper we report that when the serine protease inhibitor chymostatin is used in combination with pepstatin 99-100% of total protease activity in Aspergillus cultures is inhibited. In protease assays a concentration of 30 microM chymostatin combined with 0.075 microM pepstatin was required for maximum inhibition. Inhibitor concentrations of chymostatin and pepstatin of 120 and 0.3 microM, respectively, when added to Aspergillus cultures, has no significant effect on biomass production, glucose utilization or culture pH pattern. The potential of using these protease inhibitors in cultures of recombinant Aspergillus strains producing heterologous proteins will now be investigated to determine if the previously observed recombinant protein denaturing effects of Aspergillus proteases can be negated.

A novel immobilised design for the production of the heterologous protein lysozyme by a genetically engineered Aspergillus niger strain

A novel immobilisation design for increasing the final concentration of the heterologous protein lysozyme by a genetically engineered fungus, Aspergillus niger B1, was developed. A central composition design was used to investigate different immobilised polymer types (alginate and pectate), polymer concentration [24% and 4% (w/v)], inoculum support ratios (1:2 and 1:4) and gel-inducing agent concentration [CaCl(2), 2% and 3.5% (w/v)]. Studies of the kinetics of production showed that optimum lysozyme productivity occurred after 10 days. Lysozyme production was significantly affected by polymer type, polymer concentration, and inoculum support ratio. Overall, immobilisation in Ca-pectate resulted in higher lysozyme production compared to that in Ca-alginate. Similar effects were observed when the polymer concentration was reduced. Regardless of polymer type and concentration, increasing the fungal inoculum level increased lysozyme production. A significantly higher lysozyme yield was achieved with Ca-pectate in comparison to Ca-alginate (approximately 20-23 mg l(-1) and 0.5-2 mg l(-1), respectively). The maximum lysozyme yield achieved was about 23 mg l(-1) by immobilisation in Ca-pectate 2% (w/v) with 33% (v/v) mycelium and 3.5% (w/v) gel-inducing agent (CaCl(2)). Response surface methodology was used to investigate the effect of pH and water activity (a(w)). The best medium pH was 4.5-5.0, and bead a(w) for optimum lysozyme yield was 0.94, regardless of polymer type.

Filamentous fungi as cell factories for heterologous protein production

Filamentous fungi have been used as sources of metabolites and enzymes for centuries. For about two decades, molecular genetic tools have enabled us to use these organisms to express extra copies of both endogenous and exogenous genes. This review of current practice reveals that molecular tools have enabled several new developments. But it has been process development that has driven the final breakthrough to achieving commercially relevant quantities of protein. Recent research into gene expression in filamentous fungi has explored their wealth of genetic diversity with a view to exploiting them as expression hosts and as a source of new genes. Inevitably, the progress in the 'genomics' technology will further develop high-throughput technologies for these organisms.

The molecular biology of secreted enzyme production by fungi

Enzymes from filamentous fungi are already widely exploited, but new applications for known enzymes and new enzymic activities continue to be found. In addition, enzymes from less amenable non-fungal sources require heterologous production and fungi are being used as the production hosts. In each case there is a need to improve production and to ensure quality of product. While conventional, mutagenesis-based, strain improvement methods will continue to be applied to enzyme production from filamentous fungi the application of recombinant DNA techniques is beginning to reveal important information on the molecular basis of fungal enzyme production and this knowledge is now being applied both in the laboratory and commercially. We review the current state of knowledge on the molecular basis of enzyme production by filamentous fungi. We focus on transcriptional and post-transcriptional regulation of protein production, the transit of proteins through the secretory pathway and the structure of the proteins produced including glycosylation.