Production of pectinesterase and polygalacturonase by Aspergillus niger in submerged and solid state systems

Proteomic analysis of extracellular proteins from Aspergillus oryzae grown under submerged and solid-state culture conditions

Filamentous fungi are widely used for the production of homologous and heterologous proteins. Recently, there has been increasing interest in Aspergillus oryzae because of its ability to produce heterologous proteins in solid-state culture. To provide an overview of protein secretion by A. oryzae in solid-state culture, we carried out a comparative proteome analysis of extracellular proteins in solid-state and submerged (liquid) cultures. Extracellular proteins prepared from both cultures sequentially from 0 to 40 h were subjected to two-dimensional electrophoresis, and protein spots at 40 h were identified by peptide mass fingerprinting using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. We also attempted to identify cell wall-bound proteins of the submerged culture. We analyzed 85 spots from the solid-state culture and 110 spots from the submerged culture. We identified a total of 29 proteins, which were classified into 4 groups. Group 1 consisted of extracellular proteins specifically produced in the solid-state growth condition, such as glucoamylase B and alanyl dipeptidyl peptidase. Group 2 consisted of extracellular proteins specifically produced in the submerged condition, such as glucoamylase A (GlaA) and xylanase G2 (XynG2). Group 3 consisted of proteins produced in both conditions, such as xylanase G1. Group 4 consisted of proteins that were secreted to the medium in the solid-state growth condition but trapped in the cell wall in the submerged condition, such as alpha-amylase (TAA) and beta-glucosidase (Bgl). A Northern analysis of seven genes from the four groups suggested that the secretion of TAA and Bgl was regulated by trapping these proteins in the cell wall in submerged culture and that secretion of GlaA and XynG2 was regulated at the posttranscriptional level in the solid-state culture.

Characteristics of alpha-glucosidase production from recombinant Aspergillus oryzae by membrane-surface liquid culture in comparison with various cultivation methods

alpha-Glucosidase was produced using recombinant Aspergillus oryzae by membrane-surface liquid culture (MSLC), a method previously developed by the authors and the results compared with other methods, including shaking flask culture (SFC), agar-plate culture (APC), culture on urethane sponge supports (USC), and liquid surface culture (LSC) to determine possible reasons for the advantageous features of MSLC. When yeast extract was used as a nitrogen source, the amount of enzyme produced by MSLC was 5 or more times higher than those for SFC and LSC, but similar to that using APC. Enzyme production in USC was slightly lower than in MSLC and APC. Cell growth was similar irrespective of the cultivation method used. When NaNO3, a typical inorganic nitrogen source was used, enzyme production in all the cultures was lower than that using yeast extract. However, even using NaNO3, the amount of the enzyme produced by MSLC was 8 to 20 times higher than those by SFC, APC, USC, and LSC. Although cell growth using NaNO3 was similar to that for yeast extract in MSLC, it was markedly decreased in SFC, APC, and LSC. The reason for the difference in enzyme productivity for various cultivation methods using yeast extract and NaNO3 as a nitrogen source is discussed, on the basis of the experimental findings. The role of the oxygen transfer effect and gene expression levels in enzyme production were also examined.

Solid-state fermentation systems-an overview

Starting with a brief history of solid-state fermentation (SSF), major aspects of SSF are reviewed, which include factors affecting SSF, biomass, fermentors, modeling, industrial microbial enzymes, organic acids, secondary metabolites, and bioremediation. Physico-chemical and environmental factors such as inoculum type, moisture and water activity, pH, temperature, substrate, particle size, aeration and agitation, nutritional factors, and oxygen and carbon dioxide affecting SSF are reviewed. The advantages of SSF over Submerged Fermentation (SmF) are indicated, and the different types of fermentors used in SSF described. The economic feasibilities of adopting SSF technology in the commercial production of industrial enzymes such as amylases, cellulases, xylanase, proteases, phytases, lipases, etc., organic acids such as citric acid and lactic acid, and secondary metabolites such as gibberellic acid, ergot alkaloids, and antibiotics such as penicillin, cyclosporin, cephamycin and tetracyclines are highlighted. The relevance of applying SSF technology in the production of mycotoxins, biofuels, and biocontrol agents is discussed, and the need for adopting SSF technology in bioremediation of toxic compounds, biological detoxication of agro-industrial residues, and biotransformation of agro-products and residues is emphasized.

Influence of pectin and glucose on growth and polygalacturonase production by Aspergillus niger in solid-state cultivation

The solid-state production of endo- and exo-polygalacturonases (PG) by Aspergillus niger was studied in a media containing wheat bran, salts, and different citric pectin and/or glucose concentrations. Kinetic analysis of the process indicated that the formation of PG and the growth of A. niger are associated processes. By increasing citric pectin from 0 to 16% (w/w), the maximum A. niger concentration (X (m)) was raised from 94 to 121 mg/g dry medium suggesting that pectin can be used by A. niger as a growth substrate besides its role as an inducer. With 16% (w/w) pectin, 281 U exo-PG/gdm and 152 U endo-PG/gdm were obtained. Otherwise, pectin concentrations from 20 to 30% (w/w) hindered both production and growth. A. niger concentrations of 108-113 mg/gdm were achieved in runs with glucose from 5 to 12% (w/w), whereas at 16 and 20% (w/w) glucose, lower X (m) values (ca. 100 mg/gdm) were measured. The addition of glucose to the wheat bran medium, up to 10% (w/w) led to maximum endo-PG titers slightly lower than those found in the absence of glucose. Nevertheless, exo-PG formation in these media was strongly increased and activities over 370 U/gdm were achieved. The results suggest that in experiments with pectin concentrations until 16% (w/w), exo-PG production was repressed by pectin-degradation products although these same substances had favored biomass growth. When glucose concentrations over 10% (w/w) were added to the media, the maximum activities of both enzymes decreased drastically, suggesting that glucose at high concentrations also exerts a repressive effect on PG production.

Recent studies of protein secretion by filamentous fungi

Filamentous fungi have been widely exploited for the homologous and heterologous protein production, because of the high capacity of their protein secretion machinery. However, the production of heterologous proteins is often limited while the production of homologous proteins can be very high. Various researches have reported the methods for overcoming this problem and some techniques, such as the fusion gene system, improve the production of heterologous proteins. Recently, the molecular biological study of solid-state culture attracts the attention, because the long history of biological studies has shown that the productivity of protein in the solid-state culture frequently exceeds the productivity of protein in the submerged culture. The recent researches of solid-state culture have revealed the new aspects of protein production in filamentous fungi. Solid-state specific gene expression was observed in the glaB and pepA genes of Aspergillus oryzae. A GC-box and HSE element of the glaB promoter region affected solid-state specific gene expression of this gene. Solid-state culture-specific release of enzymes from the cell wall was also observed in the production of beta-glucosidases in Aspergillus kawachii. Extracellular soluble polysaccharide (ESP) from A. kawachii was concerned with the location of beta-glucosidases. Moreover, ESP and the cell wall fraction of A. kawachii were shown to be involved in the stability of beta-glucosidases. The knowledge of the molecular biology of solid-state culture should provide new approaches for the production of both homologous and heterologous proteins in both submerged culture and solid-state culture of filamentous fungi.

Expression profiling of pectinolytic genes from Aspergillus niger

The expression of 26 pectinolytic genes from Aspergillus niger was studied in a wild type strain and a CreA derepressed strain, under 16 different growth conditions, to obtain an expression profile for each gene. These expression profiles were then submitted to cluster analysis to identify subsets of genes with similar expression profiles. With the exception of the feruloyl esterase encoding genes, all genes were expressed in the presence of D-galacturonic acid, polygalacturonate, and/or sugar beet pectin. Despite this general observation five distinct groups of genes were identified. The major group consisted of 12 genes of which the corresponding enzymes act on the pectin backbone and for which the expression, in general, is higher after 8 and 24 h of incubation, than after 2 or 4 h. Two other groups of genes encoding pectin main chain acting enzymes were detected. Two additional groups contained genes encoding L-arabinose and D-galactose releasing enzymes, and ferulic acid releasing enzymes, respectively. The genes encoding beta-galactosidase and the L-arabinose releasing enzymes were not only expressed in the presence of D-galacturonic acid, but also in the presence of L-arabinose, suggesting that they are under the control of two regulatory systems. Similarly, the rhamnogalacturonan acetylesterase encoding gene was not only expressed in the presence of D-galacturonic acid, polygalacturonate and sugar beet pectin, but also in the presence of L-rhamnose. The data presented provides indications for a general pectinolytic regulatory system responding to D-galacturonic acid or a metabolite derived from it. In addition, subsets of pectinolytic genes are expressed in response to the presence of L-arabinose, L-rhamnose or ferulic acid.

Temperature control in a continuously mixed bioreactor for solid-state fermentation

A continuously mixed, aseptic paddle mixer was used successfully for solid-state fermentation (SSF) with Aspergillus oryzae on whole wheat kernels. Continuous mixing improved temperature control and prevented inhomogeneities in the bed. Respiration rates found in this system were comparable to those in small, isothermal, unmixed beds, which showed that continuous mixing did not cause serious damage to the fungus or the wheat kernels. Continuous mixing improves heat transport to the bioreactor wall, which reduces the need for evaporative cooling and thus may help to prevent the desiccation problems that hamper large-scale SSF. However, scale-up calculations for the paddle mixer indicated that wall cooling becomes insufficient at the 2-m(3) scale for a rapidly growing fungus like Aspergillus oryzae. Consequently, evaporative cooling will remain important in large-scale mixed systems. Experiments showed that water addition will be necessary when evaporative cooling is applied in order to maintain a sufficiently high water activity of the solid substrate. Mixing is necessary to ensure homogeneous water addition in SSF. Automated process control might be achieved using the enthalpy balance. The enthalpy balance for the case of evaporative cooling in the paddle mixer was validated. This work shows that continuous mixing provides promising possibilities for simultaneous control of temperature and moisture content in solid-state fermentation on a large scale.