Morphology engineering of Aspergillus niger for improved enzyme production

Supplementation with silicate microparticles was used as novel approach to control the morphological development of Aspergillus niger, important as the major world source of citric acid and higher‐value enzymes, in submerged culture. With careful variation of size and concentration of the micromaterial added, a number of distinct morphological forms including pellets of different size, free dispersed mycelium, and short hyphae fragments could be reproducibly created. Aluminum oxide particles similarly affected morphology, showing that this effect is largely independent of the chemical particle composition. Image analysis of morphological development of A. niger during the cultivation process showed that the microparticles influence the morphology by collision‐induced disruption of conidia aggregates and probably also the hindrance of new spore–spore interactions in the very early stage of the process. Exemplified for different recombinant A. niger strains enzyme production could be strongly enhanced by the addition of microparticles. Linked to the formation of freely dispersed mycelium, titers for glucoamylase (GA) expressed as intracellular enzyme (88 U/mL) and fructofuranosidase secreted into the supernatant (77 U/mL), were up to fourfold higher in shake flasks. Moreover, accumulation of the undesired by‐product oxalate was suppressed by up to 90%. The microparticle strategy could be successfully transferred to fructofuranosidase production in bioreactor, where a final titer of 160 U/mL could be reached. Using co‐expression of GA with green fluorescent protein, enzyme production was localized in the cellular aggregates of A. niger. For pelleted growth, protein production was maximal only within a thin layer at the pellet surface and markedly decreased in the pellet interior, whereas the interaction with the microparticles created a highly active biocatalyst with the dominant fraction of cells contributing to production. Biotechnol. Bioeng. 2010;105: 1058–1068. © 2009 Wiley Periodicals, Inc.     

Determination of the maximum product yield from glucoamylase-producing Aspergillus niger grown in the recycling fermentor

Aspergillus niger has been grown in glucose- and maltose-limited recycling cultures to determine the maximum growth yield, the maximum product yield for glucoamylase production, and the maintenance requirements at very slow specific growth rates. Using the linear equation for substrate utilization, and using the experimental data from both recycling experiments, both the maximum growth yield, Y_xsm, and the maximum product yield, Y_psm, could be determined. The values estimated were 157 g biomass per mol maltose for Y_xsm and 100 g protein per mol maltose for Y_psm. Expressed on a C₁-basis these values are 0.52 and 0.36 C-mole per C-mol for respectively Y_xsm and Y_psm. The found value for Y_psm is half the value found for alkaline serine protease production in Bacillus lichoniformis, and it can be concluded that formation of extracellular protein is more energy consuming in filamentous fungi than in prokaryotic organisms. Maintenance requirements are no significant factor during growth of Aspergillus niger, and reported maintenance requirements are most probably due to differentiation.     

Bioenergetic consequences of glucoamylase production in carbon-limited chemostat cultures ofAspergillus niger

Aspergillus niger has been grown in glucose- and maltose-limited continuous cultures to determine the bioenergetic consequences of the production of the extracellular enzyme glucoamylase. Growth yields (g biomass per mol substrate) were high, indicating that growth was very efficient and protein production for biomass was not exceedingly energy consuming. It has been found that the energy costs for the production of this extracellular enzyme is very high. Depending on the efficiency of energy conservation the glucoamylase protein yield on ATP is between 1.3 and 2.6 g protein per mol ATP, which is equal or less than 10% of the theoretical maximum of 25.5. These high energy costs most probably have to be invested in the process of excretion. A comparison between an industrial over-producing strain and the wild typeAspergillus niger showed that this over-producing strain most probably is a regulatory mutant. Two regions of specific growth rates could be determined (one at specific growth rates lower and one at specific growth rates higher than 0.1 h^-1), which are characterized by differences in mycelium morphology and a significant deviation from linearity in the linear equation for substrate utilization. Analysis of the region of specific growth rates higher than 0.1 h^-1 yielded maintenance requirements of virtual zero. It has been concluded that for a good analysis of the growth behaviour of filamentour fungi the linear equation for substrate utilization is not suitable, since it contains no term for the process of differentiation.     

Isolation and Sequencing of a New Glucoamylase Gene from an Aspergillus niger Aggregate Strain (DSM 823) Molecularly Classified as Aspergillus tubingensis

Based on morphological characteristics the taxa included in the Aspergillus aggregate can hardly be differentiated. For that reason the phylogeny of this genus was revised several times as different criteria, from morphological to later molecular, were used. We found, comparing nucleotide sequences of the ITS-region, that the strain Aspergillus niger (DSM 823) which is claimed to be identical to the strains ATCC 10577, IMI 027809, NCTC 7193 and NRRL 2322 can be molecularly classified as Aspergillus tubingensis, exhibiting 100% identity with the A. tubingensis CBS strains 643.92 and 127.49. We amplified, cloned and sequenced a new glucoamylase gene (glaA) from this strain of A. tubingensis (A. niger DSM 823) using primers derived from A. niger glucoamylase G1. The amplified cDNA fragment of 2013 bp contained an open reading frame encoding 648 amino acid residues. The calculated molecular mass of the glucoamylase, deduced from the amino acid sequence, was 68 kDa. The nucleotide sequence of glaA showed 99% similarity with glucoamylases from Aspergillus kawachii and Aspergillus shirousami, whereas the similarity with the glucoamylase G1 from A. niger was 92% An erratum to this article is available at .     

Correlation between pellet morphology and glycopeptide antibiotic balhimycin production by Amycolatopsis balhimycina DSM 5908

Actinomycetes, a class of filamentous bacteria, are an important source of several industrially relevant secondary metabolites. Several environmental factors including the media composition affect both biomass growth and product formation. Likewise, several studies have shown that environmental factors cause changes in cellular morphology. However, the relationship between morphology and product formation is not well understood. In this study, we first characterized the effect of varying concentrations of phosphate and ammonia in defined media on pellet morphology for an actinomycete Amycolatopsis balhimycina DSM 5908, which produces balhimycin, a glycopeptide antibiotic. Our results show that higher balhimycin productivity is correlated with the following morphological features: (1) higher pellet fraction in the biomass, (2) small elongated pellets, and (3) shorter filaments in hyphal growth in the periphery of the pellets. The correlation between morphology and product formation was also observed in industrially relevant complex media. Although balhimycin production starts after 72 h with maximum production around 168 h, the morphological changes in pellets are observed as early as 24 h after commencing of the batch. Therefore, morphology may be used as an early predictor of the end-of-batch productivity. We argue that a similar strategy can be developed for other strains where morphological indicators may be used as a batch monitoring tool.     

新一代糖化酶高产菌株的选育及其工业应用

【目的】建立对糖化酶生产菌种黑曲霉随机突变文库进行筛选的方法,以获得糖化酶酶活提高的突变菌株。【方法】以一株可产糖化酶的黑曲霉菌株Aspergillus niger X1为出发菌株,经硫酸二乙酯诱变获得突变文库,采用葡萄糖的结构类似物——2-脱氧葡萄糖进行筛选,并在筛选过程中逐渐提高2-脱氧葡萄糖浓度,定向选育具有2-脱氧葡萄糖抗性、高产糖化酶的突变株。【结果】获得的高产突变菌株DG36摇瓶发酵糖化酶产量比出发菌株A.niger X1提高22.2%–33.8%,经工业水平50 m~3罐发酵测试,突变株DG36发酵128 h糖化酶活可达49094 U/m L,在相同发酵时间内,其酶活较出发菌株A.niger X1提高32.8%,发酵时间缩短16.9%。【结论】本研究开发了一种以2-脱氧葡萄糖为抗性标记选育高产糖化酶突变株的方法,所得突变株DG36遗传性状稳定,与出发菌相比具有菌丝粗壮、产酶期提前、糖化酶活高、发酵时间短、有利于发酵后处理的优点。     

Structured morphological modeling as a framework for rational strain design of Streptomyces species

Successful application of a computational model for rational design of industrial Streptomyces exploitation requires a better understanding of the relationship between morphology—dictated by microbial growth, branching, fragmentation and adhesion—and product formation. Here we review the state-of-the-art in modeling of growth and product formation by filamentous microorganisms and expand on existing models by combining a morphological and structural approach to realistically model and visualize a three-dimensional pellet. The objective is to provide a framework to study the effect of morphology and structure on natural product and enzyme formation and yield. Growth and development of the pellet occur via the processes of apical extension, branching and cross-wall formation. Oxygen is taken to be the limiting component, with the oxygen concentration at the tips regulating growth kinetics and the oxygen profile within the pellet affecting the probability of branching. Biological information regarding the processes of differentiation and branching in liquid cultures of the model organism Streptomyces coelicolor has been implemented. The model can be extended based on information gained in fermentation trials for different production strains, with the aim to provide a test drive for the fermentation process and to pre-assess the effect of different variables on productivity. This should aid in improving Streptomyces as a production platform in industrial biotechnology.     

Microtiter plate‐based cultivation to investigate the growth of filamentous fungi

Microscale bioprocessing techniques are rapidly emerging as a means to increase the speed of bioprocess design and to reduce material consumption. However, there is still a lack of suitable parallelized techniques to investigate the industrially important group of filamentous bacteria and fungi. Cultivation of filamentous organisms in shake flasks is still the favored technique for comparing and optimizing cultivation conditions of production strains at mL‐scale. In this paper, the application of a microtiter plate‐based cultivation system in combination with the filamentous fungus Aspergillus niger was investigated. A protocol for reproducible cultivation was developed and evaluated. Productivity of A. niger concerning the rose‐like aroma compound 2‐phenylethanol showed low standard deviations while regular and consistent morphologies appeared in the parallelized system. Furthermore, the effect of addition of microparticles on the morphology was investigated. The results can be used to accelerate the process development with A. niger and other filamentous organisms.     

The influence of proteases on the activity of glucoamylase from Aspergillus niger C

Summary Two proteases from Aspergillus niger C post-culture medium were isolated by fractionation on a DEAE-sepharose column and ultrafiltration. The four fractions of glucoamylase activity (GA1, GA2, GA3 and GA4) present in the medium showed different susceptibility to the influence of proteases. The effects of proteases on the different glucoamylase fractions during the growth of the fungus are demonstrated. The activity was found to decrease at the beginning of the culture, but by its end there was a stimulation of GA4 glucoamylase. After treating GA2 and GA3 with protease II, a new additional fraction of glucoamylase was detected.     

Purification,characterization, and substrate specificity of a glucoamylase with steroidal saponin-rhamnosidase activity from <Emphasis Type="Italic">Curvularia lunata</Emphasis>

It has been previously reported that a glucoamylase from Curvularia lunata is able to hydrolyze the terminal 1,2-linked rhamnosyl residues of sugar chains at C-3 position of steroidal saponins. In this work, the enzyme was isolated and identified after isolation and purification by column chromatography including gel filtration and ion-exchange chromatography. Analysis of protein fragments by MALDI-TOF/TOF™ proteomics Analyzer indicated the enzyme to be 1,4-alpha-D-glucan glucohydrolase EC 3.2.1.3, GA and had considerable homology with the glucoamylase from Aspergillus oryzae. We first found that the glucoamylase was produced from C. lunata and was able to hydrolyze the terminal rhamnosyl of steroidal saponins. The enzyme had the general character of glucoamylase, which hydrolyze starch. It had a molecular mass of 66 kDa and was optimally active at 50°C, pH 4, and specific activity of 12.34 U mg of total protein⁻¹ under the conditions, using diosgenin-3-O-α-L-rhamnopyranosyl(1→4)-[α-L-rhamnopyranosyl (1→2)]-β-D-glucopyranoside (compound II) as the substrate. Furthermore, four kinds of commercial glucoamylases from Aspergillus niger were investigated in this work, and they had the similar activity in hydrolyzing terminal rhamnosyl residues of steroidal saponin. This project was supported by the National Natural Science Foundation of China (NSFC; 30572333).     

Production of Fusarium solani f. sp. pisi cutinase in Fusarium venenatum A3/5

Fusarium venenatum A3/5 was transformed using the Aspergillus niger expression plasmid, pIGF, in which the coding sequence for the F. solani f. sp. pisi cutinase gene had been inserted in frame, with a KEX2 cleavage site, with the truncated A. niger glucoamylase gene under control of the A. niger glucoamylase promoter. The transformant produced up to 21 U cutinase l⁻¹ in minimal medium containing glucose or starch as the primary carbon source. Glucoamylase (165 U l⁻¹ or 8 mg l⁻¹) was also produced. Both the transformant and the parent strain produced cutinase in medium containing cutin.     

Effect of mycelial morphology on ergothioneine production during liquid fermentation of Lentinula edodes

The morphological type of a microorganism generally influences its metabolite production. In the present study, we investigated the effects of the mycelial morphology of shiitake (Lentinula edodes) on the production of 2-mercaptohistidine trimethylbetaine (ergothioneine, ESH) during liquid fermentation. Analyses of the distribution of ESH in mycelial cells of different morphological types revealed that the ESH content of pellets obtained from the liquid fermentation media was much greater than the content in the free mycelia and clumps. The concentration of ESH in pellets on day 15 of liquid fermentation reached 0.79 mg/g dry weight (DW), which is approximately three times the concentration found in mycelia clumps (0.28 mg/g DW) and free mycelia (0.31 mg/g DW). Macroscopic image analysis of the development and morphological changes of the pellets during a liquid fermentation period of up to 25 days indicated that pellet growth showed a highly positive correlation with the increase in ESH concentration (r ² = 0.9851). A reduced agitation rate of 50 rpm for the culture medium was suitable for pellet formation and size enlargement. The results obtained in this work would be helpful in guiding the intentional manipulation of the distribution and enrichment of ESH in L. edodes through changes in liquid fermentation conditions.     

Studies on carbohydrate moieties ofAspergillus niger glucoamylase II: Isolation,purification and characterization of glycopeptides

Six glycopeptide fractions namely GP-C₁, GP-C₂. GP-C_3a.GP-C_3b.GP-D, and GP-D₂ were isolated after exhaustive digestion of glucoamylase II (Glucozyme) fromAspergillus niger with pronase. They were purified using gel-filtration. high-voltage paper electrophoresis and ion-exchange chromatography on Dowex-50 and Dowex-1. They appeared homogeneous on electrophoresis under different conditions of pHs. The molecular weights ranged from 1600 and 4000 for these glycopeptides. Ally of them contained serine at the N-terminal end. Serine and threonine were the major amino acids with glycine, alanine, proline and tryosine present as minor constituents. Carbohydrate analysis revealed the presence of different sugars. Based on this, the glycopeptides were grouped into three types: (1) GP-C₁ and GP-C₂ containing mannose, glucose and galactose; (2) GP-C_3a, and GP-C_3b,containing mannose glucose and glucosamine; and (3) GP-D₁ and GP-D₂, containing mannose. glucose, galactose and xylose. Most sugar constituents in each glycopeptide occured in non-integral ratios implying a microheterogeneity of the carbohydrate moiety inAspergillus niger glucoamylase.     

RNase-sensitive DNA polymerase activity in cell fractions and mutants of Neurospora crassa

RNase-sensitive DNA polymerase activity (RSDP) was tested in different cell fractions of Neurospora crassa cell types and its morphological mutants. This RSDP was found localized in the microsomal pellet fraction and absent in the purified nuclear pellets isolated from different N. crassa cell types: conidia, germinated conidia, and mycelia. This enzyme is capable of synthesizing a DNA product only in the presence of all four deoxyribonucleoside-5-triphosphates and Mg²⁺. Removal of RNA from the pellet fraction by RNase strongly inhibited the DNA synthesis. The endogenous synthesis of DNA in the microsomal pellet fraction was associated with the formation of an RNA:DNA hybrid as analyzed by Cs₂SO₄ equilibrium density gradient centrifugation. The DNA product after alkali hydrolysis hybridizes with the RNA isolated from the same pellet fraction, as analyzed by elution from hydroxylapatite column at 60 C. This DNA product did not hybridize with poly(A). A few mutants tested showed this RNase-sensitive DNA polymerase activity.This work was supported in part by a contract with the U.S. Department of Energy and a grant from the U.S. Naval Research.     

Studies of a pelleted growth form of Rhizopus nigricans as a biocatalyst for progesterone 11α-hydroxylation

The noncoagulative type of pellet formation can be induced in submerged cultivation of the filamentous fungus Rhizopus nigricans. The size and constitution of the hyphal agglomerates obtained varied with changes in inoculum size and agitation speed for given media composition and cultivation conditions. The physiological state of mycelium, used for a further process of biotransformation, was estimated by following the growth kinetics, pH value and substrate utilization during submerged cultivation. Namely, differences in pellet morphology and physiology affect the ability of R. nigricans to hydroxylate progesterone at the 11α position. A repeated batch procedure revealed the best maintenance of biotransformation capacity for pellets, obtained from the growth phase of cultivation at high agitation speed and with low inoculum size.     

An X-ray microtomography-based method for detailed analysis of the three-dimensional morphology of fungal pellets

Filamentous fungi are widely used in the production of biotechnological compounds. Since their morphology is strongly linked to productivity, it is a key parameter in industrial biotechnology. However, identifying the morphological properties of filamentous fungi is challenging. Owing to a lack of appropriate methods, the detailed three-dimensional morphology of filamentous pellets remains unexplored. In the present study, we used state-of-the-art X-ray microtomography (µCT) to develop a new method for detailed characterization of fungal pellets. µCT measurements were performed using freeze-dried pellets obtained from submerged cultivations. Three-dimensional images were generated and analyzed to locate and quantify hyphal material, tips, and branches. As a result, morphological properties including hyphal length, tip number, branch number, hyphal growth unit, porosity, and hyphal average diameter were ascertained. To validate the potential of the new method, two fungal pellets were studied—one from Aspergillus niger and the other from Penicillium chrysogenum. We show here that µCT analysis is a promising tool to study the three-dimensional structure of pellet-forming filamentous microorganisms in utmost detail. The knowledge gained can be used to understand and thus optimize pellet structures by means of appropriate process or genetic control in biotechnological applications.     

Expression and secretion of barley α-amylase and A.niger glucoamylase in Saccharomyces cerevisiae

cDNAs of barley α-amylase andA. niger glucoamylase were cloned in oneE. coli-yeast shuttle plasmid resulting in the construction of expression secretion vector pMAG15. pMAG15 was transformed intoS. cerevisiae GRF18 by protoplast transformation. The barley α-amylase andA. niger glucoamylase were efficiently expressed under the control of promoter and terminator of yeast PGK gene and their own signal sequence. Over 99% of the enzyme activity expressed was secreted to the medium. The recombinant yeast strain, S.cerevisiae GRF18 (pMAG15), hydrolyzes 99% of the starch in YPS medium containing 15% starch in 47 h. The glucose produced can be used for the production of ethanol. Project supported by the Guangdong Natural Science Foundation.     

Effect of agitation intensities on fungal morphology of submerged fermentation

Both parallel fermentations with Aspergillus awamori (CBS 115.52) and a literature study on several fungi have been carried out to determine a relation between fungal morphology and agitation intensity. The studied parameters include hyphal length, pellet size, surface structure or so-called hairy length of pellets, and dry mass per-wet-pellet volume at different specific energy dissipation rates. The literature data from different strains, different fermenters, and different cultivation conditions can be summarized to say that the main mean hyphal length is proportional to the specific energy dissipation rate according to a power function with an exponent of -0.25 +/- 0.08. Fermentations with identical inocula showed that pellet size was also a function of the specific energy dissipation rate and proportional to the specific energy dissipation rate to an exponent of -0.16 +/- 0.03. Based on the experimental observations, we propose the following mechanism of pellet damage during submerged cultivation in stirred fermenters. Interaction between mechanical forces and pellets results in the hyphal chip-off from the pellet outer zone instead of the breakup of pellets. By this mechanism, the extension of the hyphae or hair from pellets is restricted so that the size of pellets is related to the specific energy dissipation rate. Hyphae chipped off from pellets contribute free filamentous mycelia and reseed their growth. So the fraction of filamentous mycelial mass in the total biomass is related to the specific energy dissipation rate as well.To describe the surface morphology of pellets, the hyphal length in the outer zone of pellets or the so-called hairy length was measured in this study. A theoretical relation of the hairy length with the specific energy dissipation rate was derived. This relation matched the measured data well. It was found that the porosity of pellets showed an inverse relationship with the specific energy dissipation rate and that the dry biomass per-wet-pellet volume increased with the specific energy dissipation rates. This means that the tensile strength of pellets increased with the increase of specific energy dissipation rate. The assumption of a constant tensile strength, which is often used in literature, is then not valid for the derivation of the relation between pellet size and specific energy dissipation rate. The fraction of free filamentous mycelia in the total biomass appeared to be a function of the specific energy dissipation in stirred bioreactors. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 715-726, 1997.     

Multiple forms of a glucoamylase inhibitory factor fromAspergillus niger and its elution after adsorption onto raw wheat starch

An inhibitory factor (IF) fromAspergillus niger, that inhibited the action of glucoamylase on raw starch, was adsorbed tightly onto raw starch but was almost completely desorbed by 0.02m sodium borate. The IF was a glycoprotein and was partially purified by ion exchange chromatography into three active fractions.