Ability of a perfluoropolymer membrane to tolerate by-products of ethanol fermentation broth from dilute acid-pretreated rice straw

A perfluoropolymer (PFP) membrane has been prepared for use in vapor permeation to separate aqueous ethanol mixtures produced from rice straw with xylose-assimilating recombinant Saccharomyces cerevisiae. PFP membranes commonly have been used for dehydration process and possess good selectivity and high permeances. The effects of by-products during dilute acid pretreatment, addition of yeast extract, and ethanol fermentation on PFP membrane performance were investigated. While feeding mixtures of ethanol (90 wt%) in water, to which individual by-products (0.1–2 g/L) were added, the PFP membrane demonstrated no clear change in permeation rate (439–507 g m⁻² h⁻¹) or separation factor (14.9–23.5) from 2 to 4 h of the process. The PFP membrane also showed no clear change in permeation rate (751–859 g m⁻² h⁻¹) or separation factor (12.5–13.8) while feeding the mixture (final ethanol conc.: 61 wt%) of ethanol and distillation of the fermentation broth using a suspended fraction of dilute acid-pretreated rice straw for 20 h. These results suggest that the PFP membrane can tolerate actual distillation liquids from ethanol fermentation broth obtained from lignocellulosic biomass pretreated with dilute acid.     

Isolation and identification of microorganisms and their aerobic biodegradation of fish-meal wastewater for liquid-fertilization

To reutilize the wastewater generated during the process of fish-meal production (FMW), seven thermophilic microorganisms were newly isolated and their characteristics of aerobic biodegradation of FMW were examined in a 5 l-bioreactor. It clearly showed that the amino-acid composition (12.54 g 100 g sample⁻¹) in the final broth of the biodegradation using 8-folds diluted FMW was almost twice that of non-biodegraded FMW. The levels of amino acids in the final broth were also comparable to those in a commercial fertilizer. When more (32-folds) diluted FMW was used as a substrate, phytotoxicity of biodegraded final broth was further reduced with disappearance of a strong unpleasant smell in the end. The final broth of biodegradation using 32-folds diluted FMW required only 2-folds dilution to meet the minimum GI criterion of a phytotoxin-free fertilizer. All the results suggest the promising potential of biodegraded FMW for the production of fertilizer, which is expected to yield high economic value.     

Production of an anti-MUC1 C595 dbFv antibody fragment in recombinant Escherichia coli

The production of C595 diabody fragment (dbFv) in Escherichia coli (E. coli) HB2151 clone has been explored. The comparison of fermentation processes mode demonstrated that a higher biomass inoculum operation enhanced C595 dbFv production. It was demonstrated that a concentration of 12.1 mg l⁻¹ broth of dbFv and a cell concentration of 23.6 g l⁻¹ broth were achieved at the end of 75 l fermentation.     

Survivability of indigenous microflora and a Salmonella typhimurium marker strain in poultry mash treated with buffered propionic acid

Buffered propionic acid (BPA) was evaluated as a potential treatment for the elimination of Salmonella spp. in poultry mash. A primary poultry isolate marker strain of Salmonella typhimurium was added as either a broth or in a dry chalk carrier form to poultry mash containing soybean meal as a protein supplement. The mash was supplemented with buffered propionic acid at 2, 4, 6, 8, 10, 20, 30, 50 and 100 g kg⁻¹ diet and samples were enumerated for indigenous aerobic bacteria, fungi and the S. typhimurium marker strain. Total indigenous aerobic bacteria and fungal populations were generally decreased by addition of more than 20 g BPA kg⁻¹, but an addition of 100 g BPA kg⁻¹ mash was usually required to achieve reductions of approximately 90% of indigenous aerobic bacteria and 99% of indigenous fungi. After 7 days of storage, 8 g BPA kg⁻¹ mash also reduced S. typhimurium populations by more than 90% in mash inoculated via chalk, while at least 50 g BPA kg⁻¹ mash was required to provide the same level of reduction in mash inoculated with a liquid culture of S. typhimurium. Although BPA does not appear to be an overly effective antimicrobial agent with respect to indigenous aerobic bacterial populations in animal feed, higher concentrations may have the potential for reducing fungal and Salmonella spp. contamination in poultry mash.     

High efficiency production of astaxanthin by autotrophic cultivation of Haematococcus pluvialis in a bubble column photobioreactor

Haematococcus pluvialis was cultivated under photoautotrophic conditions in a bubble column with fed-batch addition of nutrients, especially nitrate, and a cell number above 5 × 10⁶ cells mL⁻¹ was attained after 300 h.The reduction of nutrient concentrations accompanied by dilution of the fermentation broth and an increase in the light intensity enhanced accumulation of astaxanthin. The final astaxanthin concentration of 390 mg L⁻¹ was several times higher than ever reported. This combination of fed-batch addition of nutrients and dilution of broth for nutrient deficiency is a promising method for attainment of high cell and astaxanthin concentrations in a bubble column photobioreactor.     

Development of a microtitre plate method for determination of phenol utilization,biofilm formation and respiratory activity by environmental bacterial isolates

Twenty-five aerobic phenol-degrading bacteria, isolated from different environmental samples on phenol agar after several subcultures in phenol broth, utilized phenol (0.2 g l⁻¹) within 24 h, but removal of phenol was more rapid when other carbon sources were also present. A microtitre plate method was developed to determine growth rate, biofilm formation and respiratory activity of the strains isolated. Pseudomonas putida strains C5 and D6 showed maximum growth (as O.D. at 600 nm), P. putida D6 and unidentified bacterial strain M1 were more stable at high concentrations of phenol (0.8 g l⁻¹), and P. putida C5 formed the greatest amount of biofilm in 0.5 g phenol l⁻¹ medium. Measurement of dehydrogenase activity as reduction of triphenyl tetrazolium chloride supported data on growth rate and biofilm formation. The microtitre plate method provided a selective method for detection of the best phenol degrading and biofilm-forming microorganisms, and was also a rapid, convenient means of studying the effect of phenol concentration on growth rate and biofilm formation.     

A new type of neuron-specific aminopeptidase NAP-2 in rat brain synaptosomes

A novel neutral aminopeptidase (NAP-2) was found exclusively in the rat central nervous system (CNS). It was separated from the ubiquitous puromycin-sensitive aminopeptidase (PSA) and the neuron-specific aminopeptidase (NAP) by an automated FPLC-aminopeptidase analyzer. The activity of the neuronal aminopeptidase enriched in the synaptosomes is different from NAP and PSA in distribution and during brain development. The enzyme was purified 2230-fold to apparent homogeneity from rat brain cytosol with 4% recovery by ammonium sulfate fractionation, followed by column chromatography successively on Phenyl-Sepharose, Q-Sepharose, Sephadex G-200, and Mono Q. The single-chain enzyme with a molecular mass of 110 kDa has an optimal pH of 7.0 and a pI of 5.6. It splits β-naphthylamides of amino acid with aliphatic, polar uncharged, positively charged, and aromatic side chain. Leucyl β-naphthylamide (Leu βNA) is the best substrate with the highest hydrolytic coefficiency followed by Met βNA = Arg βNA = Lys βNA > Ala βNA > Tyr βNA > Phe βNA. The cysteine-, metallo-, glyco-aminopeptidase releases the N-terminal Tyr from Leu-enkephalin with a K_m 82 μM and a k_cat of 1.08 s⁻¹, and Met-enkephalin with a K_m of 106 μM and a k_cat of 2.6 s⁻¹. The puromycin-sensitive enzyme is most susceptible to amastatin with an IC₅₀ of 0.05 μM. The data indicate that the enzyme is a new type of NAP found in rodent. Its possible function in neuron growth, neurodegeneration, and carcinomas is discussed.     

Improving the lactic acid production of Actinobacillus succinogenes by using a novel fermentation and separation integration system

This work describes the development of a novel integrated system for lactic acid production by Actinobacillus succinogenes. Fermentation and separation were integrated with the use of a microfiltration (MF) membrane, and lactic acid was recovered by resin adsorption following MF. The fermentation broth containing residual sugar and nutrients was then recycled back into the fermenter after lactic acid adsorption. This novel approach overcame the problem of product inhibition and extended the cell growth period from 41 h to 120 h. Production of lactic acid was improved by 23% to 183.4 g L⁻¹. The overall yield and productivity for glucose were 0.97 g g⁻¹ and 1.53 g L⁻¹ h⁻¹, respectively. These experimental results indicate that the integrated system could benefit continuous production of lactic acid at high levels.     

Optimized endodextranase-epoxy CIM® disk reactor for the continuous production of molecular weight-controlled prebiotic isomalto-oligosaccharides

An epoxy-activated monolithic Convective Interaction Media (CIM^®) disk was used for the immobilization of endodextranase D8144 from Penicillium sp. (EC 3.2.1.11) in order to produce on-line isomalto-oligosaccharides (IMOs) from Dextran T40. Enzymatic parameters, molecular weight of IMOs and performance of the IMmobilized Enzymes Reactor (IMER) were investigated. The immobilization yield of enzymes was about 45.3% (w/w), and the real specific activity close to 3.26 U mg⁻¹. The K_m values did not significantly change between free (12.8 g L⁻¹) and immobilized enzymes (14.2 g L⁻¹), due to the absence of diffusional limitation. The IMER system presented more than 80% of its residual activity after 5000 column volumes, highlighting the high stability of the immobilized endodextranases. Response surface methodology was used to enhance the performance of the IMER. Depending on dextran concentrations and flow rates, specific patterns of IMOs distributions were observed during the enzymatic hydrolysis. Finally, prebiotic activity was also investigated on IMOs produced by medium conditions (flow rate 0.3 mL min⁻¹ and dextran concentrations 4% w/w) against Lactobacillus rhamnosus GG (ATCC 53103). Their scores were at least as good as two commercialized fructo-oligosaccharides (FOS), Fibrulose^® F97 and Orafti^® P95.     

Operation of a bioelectrochemical system as a polishing stage for the effluent from a two-stage biohydrogen and biomethane production process

Anaerobic bioenergy production processes including fermentative biohydrogen (BioH₂), anaerobic digestion (AD) and bioelectrochemical system have been investigated for converting municipal waste or various biomass feedstock to useful energy carriers. However, the performance of a microbial fuel cell (MFC) fed on the effluent from a two-stage biogas production process has not yet been investigated extensively in continuous reactor operation on complex substrates. In this study we have investigated the extent to which a microbial fuel cell (MFC) can reduce COD and recover further energy from the effluent of a two-stage biohydrogen and biomethane system. The performance of a four-module tubular MFC was determined at six different organic loadings (0.036–6.149 g sCOD L⁻¹ d⁻¹) in terms of power generation, COD removal efficiency, coulombic efficiency (CE) and energy conversion efficiency (ECE). A power density of 3.1 W m⁻³ was observed at the OLR = 0.572 g sCOD L⁻¹ d⁻¹, which resulted in the highest CE (60%) and ECE (0.8%), but the COD removal efficiency decreased at higher organic loading rates (35.1–4.4%). The energy recovery was 92.95 J L⁻¹ and the energy conversion efficiency, based on total influent COD was found to be 0.48–0.81% at 0.572 g sCOD L⁻¹ d⁻¹. However, the energy recovery by the MFC is only reported for a four-module reactor and improved performance can be expected with an extended module count, as chemical energy remained available for further electrogenesis.     

Estimation of the phosphorus requirement of weanling pigs fed supplemental phytase

Studies were conducted with crossbred weanling pigs to determine the level of phosphorus needed to be fed when a maize–soyabean meal–whey diet was supplemented with exogenous phytase (Natuphos™). In Trial 1, phytase was added at 1200 phytase units (PTU) kg⁻¹ as phosphorus decreased. The control diet in Phase I (0–14 days) contained 7.3 g kg⁻¹ phosphorus and in Phase II (14–28 days) contained 6.5 g kg⁻¹ phosphorus. Dietary phosphorus was calculated to decrease by 0.8, 1.6 or 2.4 g kg⁻¹ when phytase was supplemented. Chromic oxide was added for estimation of apparent absorption of phosphorus. Performance was optimum when 5.7 and 4.8 g kg⁻¹ phosphorus (analysed levels) were fed with 1200 PTU kg⁻¹ phytase in Phases I and II, respectively. The lowest dietary phosphorus levels did not reduce performance for the overall 28-day period. Apparent phosphorus digestibility was increased by phytase in Phase I when 5.7 g kg⁻¹ phosphorus was fed compared to the control diet and in Phase II when 6.0 g kg⁻¹ phosphorus was fed with phytase. Faecal phosphorus excretion decreased in both phases as dietary phosphorus decreased. Faecal phosphorus excretion was minimized at the lowest phosphorus level with no decrease in performance. The estimated requirement for dietary phosphorus, as determined by the NLIN procedure, is 5.0 g kg⁻¹ in Phase I and 4.3 g kg⁻¹ in Phase II when 1200 PTU kg⁻¹ is used. In Trial 2, phytase was supplemented at 500 PTU kg⁻¹ when phosphorus was decreased in the diet. The control diet contained 6.6 and 6.0 g kg⁻¹ phosphorus in Phases I and II, respectively, and phosphorus was calculated to decrease by 0.5, 1.0, 1.5, or 2.0 g kg⁻¹ when phytase was added. Daily gain decreased when 5.0 g kg⁻¹ phosphorus was fed in Phase I and when 4.6 or 4.2 g kg⁻¹ (analysed levels) phosphorus was fed in Phase II with 500 PTU kg⁻¹. Faecal phosphorus excretion decreased as dietary phosphorus decreased, but there were no treatment effects on apparent phosphorus digestibility. The dietary phosphorus requirement was estimated to be 5.7 and 5.0 g kg⁻¹ in Phases I and II, respectively, when phytase is fed at 500 PTU kg⁻¹. At the present recommendation of 500 PTU kg⁻¹ in starter feed, phosphorus can be decreased by 0.10 g kg⁻¹. However, higher levels of phytase are needed to actually increase apparent phosphorus digestibility.     

Hydrogen sulphide removal from air by biotrickling filter using open-pore polyurethane foam as a carrier

A study was conducted on H₂S removal in a biotrickling filter packed with open-pore polyurethane foam. Thiobacillus denitrificans was used as inoculum and a mixed culture population was developed during the process. The inhibitory effect of sulphate concentration (1.8–16.8 g L⁻¹), pH (6.9–8.6), trickling liquid velocity (TLV, 9.1–22.8 m h⁻¹), H₂S inlet concentration (20–157 ppmv) and the empty bed residence time (EBRT, 9–57 s) on the H₂S removal efficiency (RE) were thoroughly investigated. An increase in pH from 6.9 to 8.5 led to a corresponding increase in H₂S removal. In addition, an inhibitory effect of sulphate concentration was observed from 16.8 g L⁻¹ and the maximum elimination capacity was found to be 22 gS m⁻³ h⁻¹ (RE 98%). The RE was constant (98.8 ± 0.30%) for EBRT ≥ 16 s, but a decrease in the EBRT from 16 to 9 s led to a corresponding decrease in RE from 98.2 to 89.6% for a TLV of 9.1 m h⁻¹ and from 97.9 to 94.9% for a TLV of 22.8 m h⁻¹ (inlet load of 11.0 ± 0.2 gS m⁻³ h⁻¹). The sulphur oxidation capacity in the biotrickling filter was not diminished by the presence of other bacteria.     

A high pressure liquid chromatography-based assay for glutathione-S-transferase class distinction assay

In order to expedite the process of classification of the members of the family of glutathione-S-transferases (GSTs) high performance liquid chromatography with photodiode array detection (HPLC-PDA) was used as a means for measuring enzymatic activity. The GST chosen for the development of the HPLC-PDA technique was from equine liver (E-GST). The characterizing substrates, ethacrynic acid (EA) and bromosulfophthalein (BSP), along with previously gathered characterization data allowed for the distinction of α, μ or π-class enzymes. In an initial characterization of the previously unclassified E-GST it was determined that the enzyme was of the π-class with specific activities of 0.062, ± 0.0015 μmol min^− 1 mg^− 1 and 0.0019, ± 0.00064 μmol min^− 1 mg^− 1 for EA and BSP, respectively. Finally, the activity of the E-GST with the EA and BSP substrates, was measured by HPLC-PDA, and was found to be 0.027, ± 0.003 μmol min^− 1 mg^− 1 and 0.002, ± 0.0005 μmol min^− 1 mg^− 1, respectively. While the HPLC-PDA data do not mirror the spectrophotometric results quantitatively the overall response by the E-GST was the same. In general, the E-GSTs were shown to belong to the π-class when characterized by HPLC-PDA due to an EA specific activity greater than 0.01 μmol min^− 1 mg^− 1 and a negligible BSP activity (≤ 0.002 μmol min^− 1 mg^− 1).     

Performance evaluation and effects of hydraulic retention time and mass loading rate on treatment of woodwaste leachate in surface-flow constructed wetlands

Four surface-flow mesocosm wetlands were operated at different hydraulic retention times during two periods to treat diluted woodwaste leachate that was acidic, of very high oxygen demand, and toxic. Temperature, dissolved oxygen, and redox potential decreased with increasing water depth. However, there was no significant vertical variation in microbial biomass. No significant development in biomass of planktonic microorganisms was found over 6 weeks of initial operation. It took <1–6 weeks for maturation of the biofilm on submerged plant surfaces and the sedimentary microbial community. Mass reduction efficiencies of chemical oxygen demand, and tannin and lignin increased significantly with hydraulic retention time when 10% leachate was fed with tap water. When a more recalcitrant influent was fed, there was a slight increase of reduction efficiency with increasing hydraulic retention time. Reduction rates increased linearly with mass loading rates up to 0.4 kg m⁻³ d⁻¹ chemical oxygen demand and 0.13 kg m⁻³ d⁻¹ tannin and lignin. Precipitation and evapotranspiration had profound impacts on the overall performance and its variability. Mass balance-based operating data of wetlands with a mature microbial community are required for proper performance assessment.     

Non-phytin phosphorus requirements of commercial broilers and White Leghorn layers

Experiments were conducted to determine the optimum requirements of non-phytin phosphorus (NPP) in commercial broilers and White Leghorn layers. Five levels of NPP (2.5, 3.0, 3.5, 4.0 and 4.5 g kg⁻¹ diet) were tested to assess the NPP requirement of commercial broilers (3–30 days of age) fed maize–soya diets containing 10 g Ca kg⁻¹. Each level of NPP was fed to quadruplicate groups of ten chicks each. Inclusion of graded levels of NPP significantly (P < 0.01) influenced body weight gain, feed intake, tibia ash content, phosphorus content in serum, tibia ash and phosphorus retention. The predicted NPP requirements for body weight gain, P content in serum and tibia ash were 4.4, 4.48 and 4.1 g kg⁻¹ diet, respectively. The NPP requirement for tibia ash was the highest (7.4 g kg⁻¹ diet). Similarly, four levels of NPP (2.0, 2.5, 3.0 and 3.5 g kg⁻¹ diet) were tested with maize–soya diets containing 35 g Ca kg⁻¹ for White Leghorn layers (266–350 days of age). Each diet was tested on four groups of 12 hens in each. Egg production was not influenced by the variation in dietary NPP levels. The predicted NPP requirements for better egg weight and shell thickness were 2.6 and 2.4 g kg⁻¹ diet, respectively, while for the serum inorganic P level the value was 3.42 g kg⁻¹ diet. Therefore, it can be concluded that commercial broilers need about 4.4 g NPP kg⁻¹ diet for better performance, whereas, White Leghorn layers need not more than 2.0 g NPP kg⁻¹ diet for better egg production. However, layers require 2.6 g NPP kg⁻¹ diet to produce eggs with better egg size and shell quality.     

Bench-scale fermentation of Trichoderma viride on wastewater sludge: Rheology,lytic enzymes and biocontrol activity

Conidiation and lytic enzyme production by Trichoderma viride at different solids concentration of pre-treated municipal wastewater sludge was examined in a 15-L fermenter. The maximum conidia concentration (5.94 × 10⁷ CFU mL⁻¹ at 96 h) was obtained at 30 g L⁻¹ suspended solids. The maximum lytic enzyme activities were achieved around 12–30 h of fermentation. Bioassay against a fungal phytopathogen, Fusarium sp. showed maximum activity in the sample drawn around 96 h of fermentation at 30 g L⁻¹ suspended solids concentration. Entomotoxicity against spruce budworm larvae showed maximum value ≈17290 SBU μL⁻¹ at 30 g L⁻¹ suspended solids concentration at the end of fermentation (96 h). Plant bioassay showed dual action of T. viride, i.e., disease prevention and growth promotion. The rheological analyses of fermentation sludges showed the pseudoplastic behaviour. In order to maintain required dissolved oxygen concentration ≥30%, the agitation and aeration requirements significantly increased at 35 g L⁻¹ compared to 30 and 25 g L⁻¹. The oxygen uptake rate and volumetric oxygen mass transfer coefficient, k_La at 35 g L⁻¹ did not increase in comparison to 30 g L⁻¹ due to rheological complexity of the broth during fermentation. Thus, the successful fermentation operation of the biocontrol fungus T. viride is a rational indication of its potential for mass-scale production for agriculture and forest sector as a biocontrol agent.     

Comparison of two matrices for selective recovery of C595 diabody fragment (dbFv) from Escherichia coli lysates

A comparative study of the performance of two types of adsorbent (Streamline Quartz Base and Upfront Matrices), derivatized with the same affinity ligand (RPAP) to recover C595 diabody fragment (dbFv) from Escherichia coli lysates has been undertaken. Both streamline and Upfront Matrices are characterized by a particle size range of 100–300 μm. Streamline has a density of 1.20 g cm⁻³ and ligand concentration of 0.85 μmol ml⁻¹. Upfront has a density of 1.35 g cm⁻³ and ligand concentration of 0.83 μmol ml⁻¹. The release of C595 dbFv from E. coli cells was achieved by a chemical lysis method. The recovery performance of both adsorbents was evaluated in terms of operational productivity and elution yield of C595 dbFv in packed bed (clarified feedstock) and expanded bed (unclarified and clarified feedstock) chromatography systems. Streamline and Upfront adsorbents exhibited diabody operational productivities of 131 and 202 mg l⁻¹, respectively, with an elution yield of 92 and 94%, respectively, in packed bed operation. Streamline and Upfront adsorbents exhibited diabody operational productivities of 54.5 and 123.7 mg l⁻¹, respectively, with an elution yield of 89 and 92%, respectively, in expanded bed operation.     

Patch dynamics of the Mediterranean seagrass Posidonia oceanica: Implications for recolonisation process

Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year⁻¹). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m⁻², and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m⁻² year⁻¹) exceeded mean patch loss (0.001 ± 0.001 patches m⁻² year⁻¹), yielding positive net patch recruitment (0.004 ± 0.003 patches m⁻² year⁻¹) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m⁻²). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m⁻², August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m⁻² year⁻¹) and loss (0.24 patches m⁻² year⁻¹) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m⁻²). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year⁻¹) increased linearly with patch size (R² = 0.64, p < 4 × 10⁻⁵, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year⁻¹), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.     

High cell density fed-batch fermentation for the production of a microbial lipase

Extracellular lipase of the yeast Candida rugosa was produced via high cell density fed-batch fermentations using palm oil as the sole source of carbon and energy. Feeding strategies consisted of a pH-stat operation, foaming-dependent control and specific growth rate control in different experiments. Compared to foaming-dependent feeding and the pH-stat operation, the specific growth rate control of feeding proved to be the most successful. At the specific growth rate control set at 0.05 h⁻¹, the final lipase activity in the culture broth was the highest at ∼700 U L⁻¹. This was 2.6-fold higher than the final enzyme activity obtained at a specific growth rate control set at 0.15 h⁻¹. The peak enzyme concentration achieved using the best foaming-dependent control of feeding was around 28% of the peak activity attained using the specific growth rate control of feeding at 0.05 h⁻¹. Similarly, the peak enzyme concentration attained using the pH-stat feeding operation was a mere 9% of the peak activity attained by specific growth rate control of feeding at a set-point of 0.05 h⁻¹. Fed-batch fermentations were performed in a 2 L stirred-tank bioreactor (30 °C, pH 7) with the dissolved oxygen level controlled at 30% of air saturation.     

Over-production of human interferon-γ by HCDC of recombinant Escherichia coli

A simple fed-batch process was developed using a modified variable specific growth rate feeding strategy for high cell density cultivation of Escherichia coli BL21 (DE3) expressing human interferon-gamma (hIFN-γ). The feeding rate was adjusted to achieve the maximum attainable specific growth rate during fed-batch cultivation. In this method, specific growth rate was changed from a maximum value of 0.55 h⁻¹ at the beginning of feeding and then it was reduced to 0.4 h⁻¹ at induction time.The final concentration of biomass and IFN-γ was reached to ∼115 g l⁻¹ (DCW) and 42.5 g(hIFN-γ) l⁻¹ after 16.5 h, also the final specific yield and overall productivity of recombinant hIFN-γ (rhIFN-γ) were obtained 0.37 g(hIFN-γ) g⁻¹ DCW and 2.57 g(hIFN-γ) l⁻¹ h⁻¹, respectively. According to available data this is the highest specific yield and productivity that has been reported for recombinant proteins production yet.