Specific Consumption Rate Research Articles

Neural network modelling of continuous microbial cultivation accounting for the memory effects

Three approaches to the problem of Neural Network (NN) modelling of chemostat microbial culture accounting for the memory effects are considered and, based on the results they are compared. The first approach uses feedforward NNs with time delay feedback connections from and to the output neurons, for the entire process modelling. The second and third approach relay on Hybrid NN modelling. The second one applies feedforward NNs with time delayed inputs for the specific growth rate approximation within the framework of the classical unstructured model. In this case the specific consumption rate is assumed to be proportional to the specific growth rate. The yield factor is assumed to be constant or polynomial function of the substrate concentration. The third approach is also based on a classical unstructured model, but different feedforward NNs with delay elements for both specific growth rate and specific consumption rate approximation are adopted. On the example of the growth of a strain Saccharomyces cerevisiae on a glucose limited medium different NN topologies are studied and a suitable model is figured out.

Replacement of the glucose phosphotransferase transport system by galactose permease reduces acetate accumulation and improves process performance of Escherichia coli for recombinant protein production without impairment of growth rate

Acetate accumulation under aerobic conditions is a common problem in Escherichia coli cultures, as it causes a reduction in both growth rate and recombinant protein productivity. In this study, the effect of replacing the glucose phosphotransferase transport system (PTS) with an alternate glucose transport activity on growth kinetics, acetate accumulation and production of two model recombinant proteins, was determined. Strain VH32 is a W3110 derivative with an inactive PTS. The promoter region of the chromosomal galactose permease gene galP of VH32 was replaced by the strong trc promoter. The resulting strain, VH32GalP + acquired the capacity to utilize glucose as a carbon source. Strains W3110 and VH32GalP + were transformed for the production of recombinant TrpLE-proinsulin accumulated as inclusion bodies (W3110-PI and VH32GalP +-PI) and for production of soluble intracellular green fluorescent protein (W3110-pV21 and VH32GalP +-pV21). W3110-pV21 and VH32GalP +-pV21 were grown in batch cultures. Maximum recombinant protein concentration, as determined from fluorescence, was almost four-fold higher in VH32GalP +-pV21, relative to W3110-pV21. Maximum acetate concentration reached 2.8 g/L for W3110-pV21 cultures, whereas a maximum of 0.39 g/L accumulated in VH32GalP +-pV21. W3110-PI and VH32GalP +-PI were grown in batch and fed-batch cultures. Compared to W3110-PI, the engineered strain maintained similar production and growth rate capabilities while reducing acetate accumulation. Specific glucose consumption rate was lower and product yield on glucose was higher in VH32GalP +-PI fed-batch cultures. Altogether, strains with the engineered glucose uptake system showed improved process performance parameters for recombinant protein production over the wild-type strain.

Latent Pathway Activation and Increased Pathway Capacity Enable Escherichia coli Adaptation to Loss of Key Metabolic Enzymes

The ability of biological systems to adapt to genetic and environmental perturbations is a fundamental but poorly understood process at the molecular level. By quantifying metabolic fluxes and global mRNA abundance, we investigated the genetic and metabolic mechanisms that underlie adaptive evolution of four metabolic gene deletion mutants of Escherichia coli (delta pgi, delta ppc, delta pta, and delta tpi) in parallel evolution experiments of each mutant. The initial response to the gene deletions was flux rerouting through local bypass reactions or normally latent pathways. The principal effect of evolution was improved capacity of already active pathways, whereas new flux distributions were not observed. Combinatorial changes in capacity and pathway activation, however, led to different intracellular flux states that enabled evolution in three of the four parallel cases tested. The molecular bases of the evolved phenotypes were then elucidated by global mRNA transcript analyses. Activation of latent pathways and flux changes in the tricarboxylic acid cycle were found to correlate well with molecular changes at the transcriptional level. Flux alterations in other central metabolic pathways, in contrast, were apparently not connected to changes in the transcriptional network. These results give new insight into the dynamics of the evolutionary process by demonstrating the flexibility of the metabolic network of E. coli to compensate for genetic perturbations and the utility of combining multiple high throughput data sets to differentiate between causal and noncausal mechanistic changes.

Effects of Hydrodynamics on Aggregates Formation, Growth and Metabolism of HEK 293 Cells in Suspension Culture

By using the size distribution of cell aggregates, viable cell density, cell viability, specific consumption rate of glucose q glc), specific production rate of lactate ( q lac), and yield of lactate from glucose ( Y lac/glc) as the evaluation indexes, the effects of hydrodynamics on aggregates formation, growth and metabolism of HEK 293 cells in suspension culture were examined in 250 mL spinner flasks by setting the agitation rates at 25, 50, 75, and 100 r/min, respectively. It was found that agitation plays an important role in HEK 293 cell aggregates formation and cell aggregates size distribution. After 7 days of cultivation in spinner flasks operated at 50 r/min and 75 r/min, the average diameter of HEK 293 cell aggregates was 201 μm and 175 μm, respectively, with the fraction of aggregates larger than or equivalent to 225 μm less than 10 %. The cell viability was kept above 90 % with the metabolic indexes, including q glc, q lac, and Y lac/glc kept constant. These results demonstrated that hydrodynamics derived from the proper agitation of the impeller play a decisive role in controlling the formation and size distribution of HEK 293 cell aggregates, and provided sufficient mass transfer to support the normal growth and metabolism of HEK 293 cells in suspended aggregates.

TESTS OF BIOACCUMULATION MODELS FOR POLYCHLORINATED BIPHENYL COMPOUNDS: A STUDY OF YOUNG-OF-THE-YEAR BLUEFISH IN THE HUDSON RIVER ESTUARY, USA

A field-based study regarding uptake of polychlorinated biphenyl compounds (PCBs) by young-of-the-year (YOY) bluefish (Pomatomus saltatrix) was initiated to test a steady-state model of bioaccumulation and trophic transfer in a rapidly growing fish. Determination of prey composition as well as size-dependent growth and specific consumption rates for YOY bluefish from separate field and laboratory studies enabled the input of these species-specific parameters into the model. Furthermore, the time and duration of the exposure of YOY bluefish to dissolved PCBs from a well-characterized system (Hudson River, USA) was well known. Patterns of accumulation of individual PCB congeners differed relative to the accumulation of total PCBs, with the greatest net accumulation occurring for the higher-molecular-weight congeners. Comparison of lipid-normalized bioaccumulation factors (BAFs) with the octanol-water partition coefficients of individual PCB congeners revealed bluefish to be above the BAFs predicted by lipid-based equilibrium partitioning, suggesting that uptake from food is an important source of PCBs in YOY bluefish. Comparison of measured BAFs with values predicted by a steady-state, food-chain model showed good first-order agreement.

The effect of temperature and carbon source on denitrification using volatile fatty acids

This study explored the effect of temperature and carbon source on the denitrification process. Batch experiments were conducted within the 10–30 °C range, using either acetic acid, propionic acid or an 1:1 mixture (by weight) of the same acids as an external carbon source. A 5 M NaNO 3 solution was added to yield nitrate-nitrogen concentrations of 50, 100 and 200 mg/L, and carbon to nitrogen (C:N) ratios of 2:1 and 4:1, respectively. It was observed that denitrification was feasible under all conditions investigated, provided that the initial reactor pH was adjusted to approximately 6.5. Overall, a temperature change from 10 to 20 °C exerted a greater effect on both the specific denitrification and carbon consumption rates than a further temperature increase from 20 to 30 °C, which was also evident in the corresponding temperature coefficient values. At a given temperature, the specific denitrification rate appeared to depend on the initial nitrogen concentration, while the specific carbon consumption rate was a function of the initial carbon content. Furthermore, a C:N ratio of 2:1 was sufficient for complete denitrification at all temperatures and types of carbon investigated. During the mixed VFA experiments, acetic acid was utilized faster than propionic acid, indicating a preferential utilization pattern. Finally, substantial alkalinity recovery was also observed in all runs, in accordance with the theoretically calculated values.

Enhanced growth in NS0 cells expressing aminoglycoside phosphotransferase is associated with changes in metabolism, productivity, and apoptosis

Prior work has reported that cotransfecting a gene of interest with the selectable marker neo can seriously perturb a number of cellular processes. In this study the influence of the neo gene on the growth, death, and metabolism of a murine myeloma NS0 cell line, expressing a chimeric antibody, was investigated. A pool of neo transfectants, 6A1-NEO, was selected with 500 microg/mL G418. Quantitative PCR analysis revealed that 6A1-NEO contained, on average, three copies of the neo gene per cell. Batch cultivation of 6A1-NEO showed that there was a 36% increase in maximum viable cell concentration, a 20% increase in the maximum apparent growth rate, and a 134% increase in cumulative cell hours as compared with the parent, 6A1-(100)3. Batch cultivation of five randomly selected clones illustrated that 6A1-NEO's advantage over the parent was not due to clonal variation. Neither the use of G418 during the selection process nor the cultivation of cells in the presence of G418 were responsible. This implied that the neo gene product, APH(3')-II, was causing the changes in proliferative capacity. Analysis of the cell cycle revealed that there were no differences in the distribution of cells in the G(1), S, and G(2) phases. When cell growth was synchronized, there were no observed differences in cell-cycle duration. 6A1-NEO resisted the onset of apoptosis during the growth phase. Consequently, there was a larger viable population of 6A1-NEO cells available for proliferation as compared with the parent. However, 6A1-NEO died at the same rate as the parent when resuspended in spent media or after treatment with staurosporin. Expression of the anti-apoptotic protein Bcl-2 was upregulated in 6A1-NEO, indicating that APH(3')-II could be acting by modulating endogenous gene expression. Analysis of key metabolites showed that 6A1-NEO's specific glucose consumption rate was 133% higher, whilst its specific glutamate consumption rate was 45% lower than the parent. 6A1-NEO's efficient utilization of glutamate and shift towards glucose metabolism may have contributed to the rise in proliferative capacity. However, this was accompanied by a 70% drop in the specific antibody production rate. These results show that the increase in growth rate and proliferative capacity caused by the expression of recombinant APH(3')-II was associated with changes in metabolism, apoptosis, and endogenous gene expression.

Participation of the Entner–Doudoroff pathway inEscherichia colistrains with an inactive phosphotransferase system (PTS–Glc+) in gluconate and glucose batch cultures

The activity of the enzymes of the central metabolic pathways has been the subject of intensive analysis; however, the Entner-Doudoroff (ED) pathway has only recently begun to attract attention. The metabolic response to edd gene knockout in Escherichia coli JM101 and PTS- Glc+ was investigated in gluconate and glucose batch cultures and compared with other pyruvate kinase and PTS mutants previously constructed. Even though the specific growth rates between the strain carrying the edd gene knockout and its parent JM101 and PTS- Glc+ edd and its parent PTS- Glc+ were very similar, reproducible changes in the specific consumption rates and biomass yields were obtained when grown on glucose. These results support the participation of the ED pathway not only on gluconate metabolism but on other metabolic and biochemical processes in E. coli. Despite that gluconate is a non-PTS carbohydrate, the PTS- Glc+ and derived strains showed important reductions in the specific growth and gluconate consumption rates. Moreover, the overall activity of the ED pathway on gluconate resulted in important increments in PTS- Glc+ and PTS- Glc+ pykF mutants. Additional results obtained with the pykA pykF mutant indicate the important contribution of the pyruvate kinase enzymes to pyruvate synthesis and energy production in both carbon sources.

Development of a fed-batch culture process for enhanced production of recombinant human antithrombin by Chinese hamster ovary cells

Antithrombin is a serine protease inhibitor that inactivates several coagulation proteases, primarily thrombin and factor Xa. The Chinese hamster ovary (CHO) cell line transfected with a vector expressing recombinant human antithrombin (rAT) and a selectable marker, glutamine synthetase (GS), was cultivated in a 2-l fed-batch culture process using serum-free, glutamine-free medium. To maximize the rAT yield, effects of culture pH, balanced amino acid feeding, and an increased glutamate concentration on cell metabolism and rAT production were investigated. When cells were grown at pH values of 6.6, 6.8, 7.0, and 7.2, the maximum cell density and maximum lactate concentration decreased with decreasing pH. The highest production level of rAT was obtained at culture pH 6.8 due to the extended culture lifetime. Compared to the imbalanced amino acid feeding at culture pH 6.8, the balanced amino acid feeding increased the amount of rAT activity by 30% as a result of an increased viable cell number. A decrease in the specific glucose consumption rate (q(Glc)) with increasing culture time was observed in all the above-mentioned experiments, while the glucose concentration was maintained above 0.7 g l(-1). In addition, a decrease in the specific rAT production rate (q(rAT)) was observed after the depletion of lactate in the late cultivation stage. Taken together, these results suggest that the reduced availability of cellular energy caused by the decrease in q(Glc) and depletion of lactate led to the decrease in q(rAT). This decrease in q(rAT) was partially prevented by increasing the residual glutamate concentration from 1 mM to 7 mM, thus resulting in an additional 30% increase in the amount of rAT activity. The optimized fed-batch culture process yielded 1.0 g l(-1) rAT at 287 h of cultivation.

Kinetics of Enhanced Substrate Consumption and Endo-β-xylanase Production by a Mutant Derivative of Humicola lanuginosa in Solid-state Fermentation

Industrial byproducts namely canola meal, rice bran, sunflower meal, and wheat straw were used as substrates for endo-xylanase production by Humicola lanuginosemutant TH1 through solid substrate fermentation. The enzyme was secreted extracellularly by both wild and mutant cultures. Rice bran supported the maximum production of endo-xylanase followed by wheat straw, canola meal and sunflower meal. The highest activity was achieved after 72 h of culture and the highest yields from the above substrates were 842, 840, 610 and 608 IU per g substrate consumed respectively. The highest productivity (281 IU flask−1 h−1 corresponding to 5620 l−1 h-1) of endo-xylanase by the mutant of H. lanuginosa was 1.6-fold more than that produced by the parental organism in solid-state fermentation of rice bran at 45 °C. Maximum specific activity (180 IU mg−1 protein) and substrate consumption rates were significantly more than those reported by previous researchers on Humicola sp. The mutant possessed markedly low accompanying cellulase activity. Thermodynamic studies revealed that the mutant required significantly lower activation energy for enzyme production and higher for thermal inactivation which signified that the endogenous metabolic machinery of mutant cells exerted more protection against thermal inactivation during product formation than that needed by its parental cultures.

Simulation of oxygen regime of tree substrates

The oxygen regime of urban tree-growing sites may be sub-optimal for tree growth and the related ornamental value of trees. Problems may especially occur in situations where the substrate is covered by pavement and/or where the water table is very shallow. The stability (oxygen consumption rate) of the organic components of the substrate (peat, green waste compost, etc.) and the design of the growing site also play an important role. The oxygen regime of a number of designs (wide strip of substrate; narrow strip; wide strip with multiple aeration pipes; narrow strip with one aeration pipe) was simulated for a range of substrates with the computer program “Matlab, pde toolbox”. The program computed equilibrium distributions of oxygen in the substrates from gas diffusion coefficients of the different parts of the growing site constructions and from the specific oxygen consumption rate of the substrate. The simulation results were compared with measurements on an experimental substrate strip. The simulation results clearly showed the importance of organic matter stability and growing site design. On wide strips the presence of aeration pipes may be very advantageous, or even necessary.

Monitoring Chinese hamster ovary cell culture by the analysis of glucose and lactate metabolism

Monitoring cell growth is crucial to the success of an animal cell culture process that can be accomplished by a variety of direct or indirect methodologies. Glucose is a major carbon and energy source for cultured mammalian cells in most cases, but glycolytic metabolism often results in the accumulation of lactate. Glucose and lactate levels are therefore routinely measured to determine metabolic activities of a culture. Typically, neither glucose consumption rate nor lactate accumulation rate has a direct correlation with cell density due to the changes in culture environment and cell physiology. We discovered that although the metabolic rate of glucose or lactate varies depending on the stages of a culture, the cumulative consumption of glucose and lactate combined ( Q GL) exhibits a linear relationship relative to the integral of viable cells (IVC), with the slope indicating the specific consumption rate of glucose and lactate combined ( q GL). Additional studies also showed that the q GL remains relatively constant under different culture conditions. The insensitivity of the q GL to process variations allows a potentially easy and accurate determination of viable cell density by the measurement of glucose and lactate. In addition, the more predictable nature of a linear relationship will aid the design of better forward control strategies to improve cell culture processes.

Effect of ldhA gene deletion on the metabolism of Escherichia coli based on gene expression, enzyme activities, intracellular metabolite concentrations, and metabolic flux distribution

To investigate how the central metabolism of Escherichia coli changes with the deletion of ldhA (lactate dehydrogenase gene), an integrated study was made by combining the information of cultivation characteristics, gene expressions, enzyme activities, intracellular metabolite concentrations, and metabolic flux distribution. The deletion of ldhA gene reduced the specific growth rate and the specific glucose consumption rate. The production rates of acetate, ethanol, and formate were all higher for the ldhA mutant as compared with those of the parent strain. The anaplerotic enzyme phosphoenol pyruvate carboxylase (Ppc), which is also known to be contributed to catabolic succinate formation under anaerobic condition, was downregulated in the ldhA mutant compared to the parent strain. On the other hand, phosphoenol pyruvate carboxykinase (Pck) that catalyzes the opposite reaction to Ppc was upregulated significantly in the mutant. This was mainly due to the shortage of phosphoenol pyruvate (PEP) in the ldhA mutant as was evidenced by the measurement of intracellular PEP concentration. Interestingly, two other catabolic enzymes, NAD +- and NADP +-specific malic enzymes, were both shown to be present in the parent E. coli but regulated differently in ldhA mutant. The activity of NADP +-specific malic enzyme encoded by maeB remained unchanged, whereas NAD +-specific malic enzyme encoded by sfcA was found to be upregulated significantly in the ldhA mutant compared to those in the parent strain implying that the inactivation of ldhA gene leads to the production of malate from pyruvate. Moreover, it was found that ldhA gene deletion induced a stress response as was evidenced by the significant upregulation of the genes dnaJ, grpE, groS, and fkpA involved in the heat shock response.

Small‐Scale Extrusion of Corn Masa By‐Products

ABSTRACTCorn masa by‐product streams are high in fiber and are amenable for utilization in livestock feed rations. This approach is a potentially viable alternative to landfilling, the traditional disposal method for these processing residues. Suspended solids were separated from a masa processing waste stream, blended with soybean meal at four levels (0, 10, 20, and 30% wb), and extruded in a laboratory‐scale extruder at speeds of 50 rpm (5.24 rad/sec) and 100 rpm (10.47 rad/sec) with temperature profiles of 80‐90‐100°C and 100‐110‐120°C. Processing conditions, including dough and die temperatures, drive torque, specific mechanical energy consumption, product and feed material throughput rates, dough apparent viscosity, and dough density, were monitored during extrusion. The resulting products were subjected to physical and nutritional characterization to determine the effects of processing conditions for these blends. Extrudate analysis included moisture content, water activity, crude protein, in vitro protein digestibility, crude fat, ash, product diameter, expansion ratios, unit and true density, color, water absorption and solubility, and durability. All blends were suitable for extrusion at the processing conditions used. Blend ratio had little effect on either processing parameters or extrudate properties; extrusion temperature and screw speed, on the other hand, significantly affected both processing and product properties.

Reliability of methods for the determination of specific substrate consumption rates in batch culture

Four methods for the calculation of specific substrate consumption rates in batch cultivation were compared. Calculations based on a simple mathematical model resulted in the most reliable rate predictions. The application and accuracy of a novel, Logarithmic Method for rate estimations directly from experimental data were also demonstrated.

Growth and metabolism of marine fish Chinook salmon embryo cells: response to lack of glucose and glutamine

A peculiar phenomenon, differing from the response of mammalian cells, occurred when Chinook salmon embryo (CHSE) cells were passaged in the medium lacking of both glucose and glutamine. To elucidate metabolic mechanism of CHSE cells, the metabolism parameters, key metabolic enzymes, and ATP levels were measured at different glucose and glutamine concentrations. In the glutamine-free culture, hexokinase activity kept constant, and lactate dehydrogenase (LDH) activity decreased. This indicated that lack of glutamine did not expedite glucose consumption but made it shift to lower lactate production and more efficient energy metabolism. The results coincided with the experimental results of unaltered specific glucose consumption rate and decreased yield coefficients of lactate to glucose. In the glucose-free culture, simultaneous increase of glutaminase activity and of specific ammonia production rate suggested an increased flux into the glutaminolysis pathway, and increases of both glutamate dehydrogenase activity and yield coefficient of ammonia to glutamine showed an increased flux into deamination pathway. However, when glucose and glutamine were both lacking, the specific consumption rates of most of amino acids increased markedly, together with decrease of LDH activity, indicating that pyruvate derived from amino acids, away from lactate production, remedied energy deficiency. When both glucose and glutamine were absent, intracellular ATP contents and the energy charge remained virtually unaltered.

Physiological response of central metabolism inEscherichia colito deletion of pyruvate oxidase and introduction of heterologous pyruvate carboxylase

We studied the physiological response of Escherichia coli central metabolism to the expression of heterologous pyruvate carboxylase (PYC) in the presence and absence of pyruvate oxidase (POX). These studies were complemented with expression analysis of central and intermediary metabolic genes and conventional in vitro enzyme assays to evaluate glucose metabolism at steady-state growth conditions (chemostats). The absence of POX activity reduced nongrowth-related energy metabolism (maintenance coefficient) and increased the maximum specific rate of oxygen consumption. The presence of PYC activity (i.e., with POX activity) increased the biomass yield coefficient and reduced the maximum specific oxygen consumption rate compared to the wildtype. The presence of PYC in a poxB mutant resulted in a 42% lower maintenance coefficient and a 42% greater biomass yield compared to the wildtype. Providing E. coli with PYC or removing POX increased the threshold specific growth rate at which acetate accumulation began, with an 80% reduction in acetate accumulation observed at a specific growth rate of 0.4 h-1 in the poxB-pyc+ strain. Gene expression analysis suggests utilization of energetically less favorable glucose metabolism via glucokinase and the Entner-Doudoroff pathway in the absence of functional POX, while the upregulation of the phosphotransferase glucose uptake system and several amino acid biosynthetic pathways occurs in the presence of PYC. The physiological and expression changes resulting from these genetic perturbations demonstrate the importance of the pyruvate node in respiration and its impact on acetate overflow during aerobic growth.

Isolation of dipicolinic acid as an insecticidal toxin from Paecilomyces fumosoroseus

Several entomopathogenic fungi produce toxins that could be used as bioinsecticides in integrated pest management programs. Paecilomyces fumosoroseus is currently used for the biological control of the whiteflies Bemisia tabaci and B. argentifolii. Supernatants from submerged batch culture, where the fungus produced abundant dispersed mycelium, conidia and blastospores, were toxic to the whitefly nymphs. The most abundant metabolite was purified by HPLC and identified by mass spectrometry and NMR as dipicolinic acid. Both the dipicolinic acid produced by the fungus and the chemically synthesized compound had insecticidal activity against third-instar nymphs of the insect. Dipicolinic acid was toxic to the whitefly nymphs in bioassays involving topical applications. In submerged culture, the specific growth rate of P. fumosoroseus was 0.054 h-1, the specific glucose consumption rate was 0.1195 g g-1 h-1 and the specific dipicolinic acid production rate was 0.00012 g g-1 h-1. Dipicolinic acid was detected after 24 h when the fungus started growing; and dipicolinic acid production was directly correlated with fungal growth. Nevertheless, the yield was low and the maximal concentration was only 0.041 g l-1. The maximal concentrations of conidia and blastospores (per milliliter) were 1.4x10(8) and 7x10(7), respectively.

Metabolic engineering of a xylose-isomerase-expressing strain for rapid anaerobic xylose fermentation

After an extensive selection procedure, Saccharomyces cerevisiae strains that express the xylose isomerase gene from the fungus Piromyces sp. E2 can grow anaerobically on xylose with a mu(max) of 0.03 h(-1). In order to investigate whether reactions downstream of the isomerase control the rate of xylose consumption, we overexpressed structural genes for all enzymes involved in the conversion of xylulose to glycolytic intermediates, in a xylose-isomerase-expressing S. cerevisiae strain. The overexpressed enzymes were xylulokinase (EC 2.7.1.17), ribulose 5-phosphate isomerase (EC 5.3.1.6), ribulose 5-phosphate epimerase (EC 5.3.1.1), transketolase (EC 2.2.1.1) and transaldolase (EC 2.2.1.2). In addition, the GRE3 gene encoding aldose reductase was deleted to further minimise xylitol production. Surprisingly the resulting strain grew anaerobically on xylose in synthetic media with a mu(max) as high as 0.09 h(-1) without any non-defined mutagenesis or selection. During growth on xylose, xylulose formation was absent and xylitol production was negligible. The specific xylose consumption rate in anaerobic xylose cultures was 1.1 g xylose (g biomass)(-1) h(-1). Mixtures of glucose and xylose were sequentially but completely consumed by anaerobic batch cultures, with glucose as the preferred substrate.

6-pentyl-α-pyrone production byTrichoderma harzianum: The influence of energy dissipation rate and its implications on fungal physiology

The influence of the agitation conditions on biomass growth, morphology, carbon metabolism, viability, and 6-pentyl-alpha-pyrone (6PP) production by Trichoderma harzianum were studied in an extractive fermentation system. Batch spore-inoculated cultures developed at dissolved oxygen concentrations above 35% of air saturation were carried out in a 14 L bioreactor. The effect of energy dissipation rate over culture performance was assessed using two sets of three Rushton turbines (having different diameters) operated at different agitation speeds. Higher mechanical stress enhanced cellular differentiation (i.e., sporulation), while yielding lower specific growth rates and increased specific CO(2) production rates (CPRs) at relatively constant specific glucose consumption rates. In addition, fungal viability and clump mean diameter decreased gradually at higher energy dissipation rates. 6PP biosynthesis was growth associated and its specific productivity showed a bell-shaped relationship with the energy dissipation rate. T. harzianum physiology was, therefore, strongly influenced by the prevailing hydrodynamic conditions as it triggered cellular metabolism and differentiation shifts.