Oocyst shedding by cats fed isolated bradyzoites and comparison of infectivity of bradyzoites of the VEG strain Toxoplasma gondii to cats and mice

Infectivity of bradyzoites of the VEG strain of Toxoplasma gondii was compared in cats and mice. For this, tissue cysts were separated from brains of infected mice using a Percoll gradient, and bradyzoites were released by incubation in acidic pepsin solution. After filtration through a 3-microm filter, bradyzoites were counted and diluted 10-fold in RPMI tissue culture medium. Dilutions estimated to have 1, 10, 100, and 1,000 bradyzoites were fed to cats and inoculated into mice, orally or subcutaneously (s.c.). Three experiments were performed. In experiment 1, 2 of 2 cats fed 1,000 bradyzoites, 1 of 2 cats fed 100 bradyzoites, 1 of 4 cats fed 10 bradyzoites, and 1 of 4 cats fed 1 bradyzoite shed millions of oocysts; 1,000 bradyzoites were infective to all 4 inoculated mice s.c. but not to 4 mice inoculated orally, and 100 bradyzoites were infective to 2 of 4 mice injected s.c. but not to 4 mice inoculated orally. All 16 mice (8 oral, 8 s.c.) injected with 1 or 10 bradyzoites were negative for T. gondii. In experiment 2, 1 of 4 cats fed 10 counted bradyzoites shed oocysts; the same inocula were not infective to 4 mice injected s.c. In experiment 3, 3 of 4 cats fed 1,000 bradyzoites shed oocysts and the inocula were infective to 10 of 10 mice s.c. and 4 of 10 mice orally; 4 of 4 cats fed 100 bradyzoites shed oocysts and the inocula were infective to 6 of 10 mice s.c. and 0 of 10 mice orally; 10 bradyzoites were not infective to cats and mice. Results indicate that bradyzoites are more infective to cats than to mice, and cats can shed millions of oocysts after ingesting just a few bradyzoites.     

Effect of iron concentration on hydrogen fermentation

The effect of the iron concentration in the external environment on hydrogen production was studied using sucrose solution and the mixed microorganisms from a soybean-meal silo. The iron concentration ranged from 0 to 4000 mgFeCl₂ l⁻¹. The temperature was maintained at 37°C. The maximum specific hydrogen production rate was found to be 24.0 mlg⁻¹ VSSh⁻¹ at 4000 mgFeCl₂ l⁻¹. The specific production rate of butyrate increased with increasing iron concentration from 0 to 20 mgFeCl₂ l⁻¹, and decreased with increasing iron concentration from 20 to 4000 mgFeCl₂ l⁻¹. The maximum specific production rates of ethanol (682 mgg⁻¹ VSSh⁻¹) and butanol (47.0 mgg⁻¹ VSSh⁻¹) were obtained at iron concentrations of 5 and 3 mgFeCl₂ l⁻¹, respectively. The maximum hydrogen production yield of 131.9 mlg⁻¹ sucrose was obtained at the iron concentration of 800 mgFeCl₂ l⁻¹. The maximum yields of acetate (389.3 mgg⁻¹ sucrose), propionate (37.8 mgg⁻¹ sucrose), and butyrate (196.5 mg g⁻¹ sucros) were obtained at iron concentrations of 3, 200 and 200 mgFeCl₂ l⁻¹, respectively. The sucrose degradation efficiencies were close to 1.0 when iron concentrations were between 200 and 800 mgFeCl₂ l⁻¹. The maximum biomass production yield was 0.283 gVSSg⁻¹ sucrose at an iron concentration of 3000 mgFeCl₂ l⁻¹.     

Cost of selective feeding by the blue mussel (Mytilus trossulus) as measured by respiration and ammonia excretion rates

The metabolic cost as measured by respiration and ammonia excretion rates associated with a selective as compared to a non-selective feeding behaviour was determined for the blue mussel, Mytilus trossulus. Mussels were challenged with four environmentally relevant seston matrices of different quality and quantity, which were known to evoke either a sorting response (i.e., selective feeding) where organic-rich particles were selected over inorganic particles as compared to no sorting (i.e., non-selective) where either inorganic or organic particles were ingested by the bivalve. Seston matrices were prepared by mixing known quantities of silt and algae such that the following extent of feeding responses would occur; no pre-sorting of ingested material, (1) no algae+50 mg silt l⁻¹, (2) 150×10⁶ cells l⁻¹ of algae+no silt, and, where pre-sorting of ingested material occurred, (3) 20×10⁶ cells l⁻¹ of algae and 20 mg l⁻¹ of silt, and (4) 150×10⁶ cells l⁻¹ of algae and 50 mg l ¹ of silt. A control, which represented basal metabolism consisting of mussels exposed only to filtered seawater (0.45 μm), was included for a total of five treatments. Mussel respiration and ammonia excretion rates were independent of whether mussels were pre-sorting or not sorting ingested material. Of the four matrices, only rates determined for conditions of maximum seston quality and quantity where pre-sorting of the seston occurred were significantly different from control mussels (p<0.05, ANOVA). Estimates of net energy used for feeding, where net energy is total energy intake (food) minus energy expenditure (energy lost through respiration and excreta as measured by ammonia excretion rates), indicated that feeding, whether selective or non-selective required only 0.92% of net energy intake. Hence, mussels appear to be highly adapted to a dynamic food environment with negligible costs associated with the feeding process, even when significant pre-selection of organic-rich particles occurs.     

High-density cultivation of Perilla frutescens cell suspensions for anthocyanin production: Effects of sucrose concentration and inoculum size

High-density cultivation of Perilla frutescens cells for anthocyanin production was carried out in both batch and fed-batch modes in a 500-ml shake flask. In fed-batch cultures, a high cell density of 27.7 g dry cells l⁻¹ and a total anthocyanin production of 3.87 g l⁻¹ by intermittent feeding of all medium components except hormones were obtained. In batch cultures, both initial sucrose concentration and inoculum size showed a conspicuous effect on the kinetics of cell growth, sugar consumption, and secondary metabolite (anthocyanins) production by suspended P. frutescens cells. At an inoculum size of 50 g wet cells l⁻¹, the maximum cell density of 38.3 g dry cells l⁻¹ was obtained after 11 days of cultivation at an initial sucrose concentration of 60 g l⁻¹, the highest pigment production of>5.8 g l⁻¹ was attained after 10 days of cultivation at an initial sucrose concentration of 45 g l⁻¹. These amounts of cell mass and anthocyanin pigments were 3.3 and 24 times higher than those at an initial sucrose concentration of 15 g l⁻¹ and inoculum size of 15 g wet cells l⁻¹, respectively.     

Effects of medium glucose concentration and pH on docosahexaenoic acid content of heterotrophic Crypthecodinium cohnii

The effects of medium glucose concentration and pH on growth and docosahexaenoic acid (DHA, C22:6 ω-3) content of Crypthecodinium cohnii were investigated. Over a range of glucose concentrations (5–40 g l⁻¹) investigated, the highest specific growth rate (0.12 h⁻¹), highest cell dry weight concentration (3.13 g l⁻¹) and highest growth yield on glucose (0.6 g g⁻¹) were obtained at 20 g l⁻¹ glucose. However, the highest degree of fatty acid unsaturation (3.2) and highest DHA proportion (53.4% of total fatty acids) were achieved at 5 g l⁻¹ glucose. Low glucose concentrations enhanced the degree of fatty acid unsaturation and DHA formation. Medium pH also affected cell growth, fatty acid unsaturation and DHA proportion. When medium pH was 7.2, the highest specific growth rate (0.089 h⁻¹), highest cell dry weight concentration (2.73 g l⁻¹), highest growth yield on glucose (0.564 g g⁻¹), highest degree of fatty acid unsaturation (3.4) and highest DHA proportion (56.8% of total fatty acids) were obtained. Results suggest that glucose concentration and pH value could be effectively manipulated to achieve maximum DHA production by C. cohnii.     

Cadmium biosorption on Spirulina platensis biomass

Dry biomass of Spirulina platensis re-hydrated for 48 h was employed as a biosorbent in tests of cadmium(II) removal from water. Various concentrations of biomass (from 1 to 4 g l⁻¹) and metal (from 100 to 800 mg l⁻¹) were tested. Low biomass levels (X_o  2 g l⁻¹) ensured metal removal up to 98% only at Cd₀= 100 and 200 mg l⁻¹, while X_o  2.0 g l⁻¹ were needed at Cd₀ = 400 mg l⁻¹ to achieve satisfactory results. Whereas X_o = 4.0 g l⁻¹ was effective to remove up to Cd₀ = 500 mg l⁻¹, a further increase in metal concentration (Cd₀ = 600 and 800 mg l⁻¹) led to progressive worsening of the system performance. At a given biomass levels, the kinetics of the process was better at low Cd²⁺ concentrations, while, raising the adsorbent level from 1.0 to 2.0 g l⁻¹ and then to 4.0 g l⁻¹, the rate constant of biosorption increased by about one order of magnitude in both cases and the adsorption capacity of the system progressively decreased from 357 to 149 mg g⁻¹.     

Effects of feed sugar concentration on continuous ethanol fermentation of cheese whey powder solution (CWP)

Cheese whey powder (CWP) solution with different CWP or sugar concentrations was fermented to ethanol in a continuous fermenter using pure culture of Kluyveromyces marxianus (DSMZ 7239). Sugar concentration of the feed CWP solution varied between 55 and 200 g l⁻¹ while the hydraulic residence time (HRT) was kept constant at 54 h. Ethanol formation, sugar utilization and biomass formation were investigated as functions of the feed sugar concentration. Percent sugar utilization and biomass concentrations decreased and the effluent sugar concentration increased with increasing feed sugar concentrations especially for the feed sugar contents above 100 g l⁻¹. Ethanol concentration and productivity (DP) increased with increasing feed sugar up to 100 g l⁻¹ and then decreased with further increases in the feed sugar content. The highest ethanol concentration (3.7%, v v⁻¹) and productivity (0.54 gE l⁻¹ h⁻¹) were obtained with the feed sugar content of 100 g l⁻¹ or 125 g l⁻¹. The ethanol yield coefficient (Y_P/S) was also maximum (0.49 gE gS⁻¹) when the feed sugar was between 100 and 125 g l⁻¹. The growth yield coefficient (Y_X/S) decreased steadily from 0.123 to 0.063 gX gS⁻¹ when the feed sugar increased from 55 to 200 g l⁻¹ due to adverse effects of high sugar contents on yeast growth. The optimal feed sugar concentration maximizing the ethanol productivity and sugar utilization was between 100 and 125 g l⁻¹ under the specified experimental conditions.     

Simultaneous production of anthocyanin and triterpenoids in suspension cultures of Perilla frutescens

When cultivated in Murashige & Skoog medium supplemented with 0.2 mg l⁻¹ 2,4-dichlorophenoxy acetic acid and 0.5 mg l⁻¹ 6-benzyladenine, Perilla frutescens cells in suspension culture grew rapidly reaching about 13.6 g dry wt l⁻¹ after 12 days. The cell line produced both anthocyanin 0.9 g l⁻¹ and triterpenoids: 16 mg l⁻¹ oleanolic acid (OA), 25 mg l⁻¹ ursolic acid (UA) and 14 mg l⁻¹ tormentic acid (TA). When P. frutescens cells of 7-day-old cultures were exposed to a yeast elicitor at 0.5–5% (v/v) for 7 days, it was found that anthocyanin content peaked at 10.2% of dry weight with yeast elicitor at 1% (v/v) whereas the maximum production of oleanolic acid and ursolic acid in cultures treated with 2% (v/v) yeast elicitor was 19 and 27 mg l⁻¹, a 46 and 24% increase over the control, respectively. This is the first report of simultaneous production of both anthocyanin and triterpenoids in a single culture system.     

Efficient plant regeneration from seedling explants of two commercially important temperate eucalypt species–Eucalyptus nitens and E. globulus

A reliable and reproducible method for plant regeneration in vitro of two important temperate eucalypts, Eucalyptus nitens and E. globulus, has been developed which utilises seedling explants. Highly regenerative callus was obtained from individual cotyledon and hypocotyledon explants of both species following cultivation on Murashige and Skoog’s (MS) basal nutrient medium supplemented with 30 g l⁻¹ sucrose, 5–10% (v/v) coconut water, 0.8% agar, 1 mg l⁻¹ -naphthalene-acetic acid (NAA) and 0.5 mg l⁻¹ N⁶ benzylaminopurine (BAP). Shoot differentiation was observed 7–8 weeks after transfer of callus onto regeneration medium containing 0.5 mg l⁻¹ NAA and 1 mg l⁻¹ BAP. In a few instances, direct shoot regeneration occurred without an intervening callus phase in both species. The frequency of plant regeneration was higher for callus derived from hypocotyl segments (30–35%) compared to cotyledonary explants (20–25%) though the average number of shoots per cotyledonary explant was generally higher than for hypocotyl explants. Somatic embryos were observed occasionally in E. nitens, arising from the surface of organogenic callus. Organised structures closely resembling somatic embryos were also observed in E. globulus. Regenerated shoots (30–40%) of both species could be rooted in modified MS media containing indole-3-butyric acid (IBA) and plantlets were successfully transferred to soil.     

Phenol inhibition of biological nutrient removal in a four-step sequencing batch reactor

Nutrient removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different phenol (C₆H₅OH) concentrations in order to determine the inhibition effects of phenol on biological nutrient removal. The nutrient removal process consisted of anaerobic, oxic, anoxic, and oxic phases with hydraulic residence times (HRT) of 1 h/3 h/1 h/1 h and a settling phase of 3/4 h. Solids retention time (SRT) was kept constant at 10 days in all experiments. Initial phenol concentrations were varied between 0 and 600 mg l⁻¹ at seven different levels. The effects of phenol on COD, NH₄-N, and PO₄-P removals and effluent nutrient levels were investigated. Phenol was almost completely degraded up to 400 mg l⁻¹ phenol concentration resulting in almost negligible inhibition effects on COD, NH₄-N, and PO₄-P removals. Nutrient removals were adversely affected by phenol at concentrations above 400 mg l⁻¹. Above 95% COD, 90% NH₄-N and 65% PO₄-P removal was obtained for phenol concentrations below 400 mg l⁻¹. The sludge volume index (SVI) was almost constant around 45 ml g⁻¹ for phenol concentrations below 400 mg l⁻¹ but increased to 90 ml g⁻¹ at a phenol level of 600 mg l⁻¹.     

Aerobic chromate reduction by chromium-resistant bacteria isolated from serpentine soil

A group of 34 chromium-resistant bacteria were isolated from naturally occurring chromium percolated serpentine soil of Andaman (India). These isolates displayed different degrees of chromate reduction under aerobic conditions. One of the 34 isolates identified as Bacillus sphaericus was tolerant to 800 mg l⁻¹ Cr(VI) and reduced >80% Cr(VI) during growth. In Vogel Bonner broth, B. sphaericus cells (10¹⁰ cells ml⁻¹) reduced 62% of 20 mg l⁻¹ of Cr(VI) in 48 h with concomitant discoloring of yellow medium to white one. Reduction of chromate was pronounced by the addition of glucose and yeast extract as electron donors. In the presence of 4.0 g l⁻¹ of glucose, 20 mg l⁻¹ of Cr(VI) was reduced to 2.45 mg l⁻¹ after 96 h of incubation. Optimum pH and temperature for reduction were 6.0 and 25 °C, respectively. Increase in cell density and initial Cr(VI) concentration increased chromate reduction but was inhibited by metal ions like, Ni²⁺, Co²⁺, Cd²⁺ and Pb²⁺. Experiments with cell-free extracts indicated that the soluble fraction of the cell was responsible for aerobic reduction of Cr(VI) by this organism.     

Studies on composition and stability of a large membered bacterial consortium degrading phenol

A ten member microbial consortium (AS) consisting of eight phenol-degrading and two non-phenol-degrading strains of bacteria was developed and maintained in a fed-batch reactor by feeding 500 mg l⁻¹ phenol for four years at 28 ± 3 °C. The consortium could degrade 99% of 500 mg l⁻¹ phenol after 24 hours incubation with a biomass increase of 2.6 × 10⁷ to 4 × 10¹² CFU ml⁻¹. Characterization of the members revealed that it consisted of 4 principal genera, Bacillus, Pseudomonas, Rhodococcus, Streptomyces and an unidentified bacterium. Phenol degradation by the mixed culture and Bacillus subtilis, an isolate from the consortium was compared using a range of phenol concentrations (400 to 700 mg l⁻¹) and by mixing with either 160 mg l⁻¹ glucose or 50 mg l⁻¹ of 2,4-dichlorophenol in the medium. Simultaneous utilization of unrelated mixed substrates (glucose/2,4-dichlorophenol) by the consortium and Bacillus subtilis, indicated the diauxic growth pattern of the organisms. A unique characteristic of the members of the consortia was their ability to oxidize chloro aromatic compounds via meta pathway and methyl aromatic compounds via ortho cleavage pathway. The ability of a large membered microbial consortia to maintain its stability with respect to its composition and effectiveness in phenol degradation indicated its suitability for bioremediation applications.     

A perfusion air-lift bioreactor for high density plant cell cultivation and secreted protein production

A new bioreactor design that allows continuous perfusion cultivation of plant cell suspensions is described in this paper. This design incorporates an internal cell settling zone with an external-loop air-lift bioreactor. The settling zone is created by inserting a baffle plate into the upper portion of the downcomer. Using this bioreactor, Anchusa officinalis suspension culture was cultivated to a cell density of 27.2 g l⁻¹ DW in 14 days at a perfusion rate of 0.123 per day. The maximum total extracellular protein concentration attained 1.11 g l⁻¹. Complete cell retention was achieved throughout the culture during which the maximum packed cell volume (PCV) exceeded 80%. In comparison, the maximum cell density and extracellular protein concentration in the batch culture were 12.6 g l⁻¹ DW and 0.47 g l⁻¹, respectively. SDS-PAGE of the extracellular protein samples revealed two major bands at 58 and 47 kDa, each accounted for approximately 45% of the total secreted proteins.     

The non-specific inhibition of enzymes by environmental pollutants: a study of a model system towards the development of electrochemical biosensor arrays

Previous research has shown that lactate dehydrogenase (LDH) was competitively inhibited by pentachlorophenol (PCP) and a modified assay produced a detection limit of 1 μM (270 μg l⁻¹). This work used spectrophotometric rate-determination but in order to move towards biosensor development the selected detection method was electrochemical. The linkage of LDH to lactate oxidase (LOD) provided the electroactive species, hydrogen peroxide. This could be monitored using a screen-printed carbon electrode (SPCE) incorporating the mediator, cobalt phthalocyanine, at a potential of +300 mV (vs. Ag/AgCl). A linked LDH/LOD system was optimised with respect to inhibition by PCP. It was found that the SPCE support material, PVC, acted to reduce inhibition, possibly by combining with PCP. A cellulose acetate membrane removed this effect. Inhibition of the system was greatest at enzyme activities of 5 U ml⁻¹ LDH and 0.8 U ml⁻¹ LOD in reactions containing 246 μM pyruvate and 7.5 μM NADPH. PCP detection limits were an EC₁₀ of 800 nM (213 μg l⁻¹) and a minimum inhibition detectable (MID) limit of 650 nM (173 μg l⁻¹). The inclusion of a third enzyme, glucose dehydrogenase (GDH), provided cofactor recycling to enable low concentrations of NADPH to be incorporated within the assay. NADPH was reduced from 7.5 to 2 μM. PCP detection limits were obtained for an assay containing 5 U ml⁻¹ LDH, 0.8 U ml⁻¹ LOD and 0.1 U ml⁻¹ GDH with 246 μM pyruvate, 400 mM glucose and 2 μM NADPH. The EC₁₀ limit was 150 nM (39.9 μg l⁻¹) and the MID was 100 nM (26.6 μg l⁻¹). The design of the inhibition assays discussed has significance as a model for other enzymes and moves forward the possibility of an electrochemical biosensor array for pollution monitoring.     

Effect of treatment with free and liposomized albendazole on selected immunological parameters and cyst growth in mice infected with Echinococcus multilocularis

Selected immunological parameters in healthy mice and mice infected with Echinococcus multilocularis and the effect of free and liposomized albendazole (lip.ABZ) upon these parameters in relation to the reduction of parasite growth were investigated over 26 weeks. Proliferative response of splenic T and B lymphocytes, number of CD4+ and CD8+ spleen T cell subpopulations, serum concentration of IFN-γ and IL-5, and generation of superoxide anion (O₂⁻) by peritoneal macrophages were the chosen parameters. Both drug forms were given to mice at a dose of 10 mg kg⁻¹ twice a week from week 4 to week 10 post infection (p.i.) (6 weeks in total). The reduction of cyst growth after treatment with ABZ and lip.ABZ was similar up to week 4 after last dose, but the parasitostatic effect of lip.ABZ lasted 4 weeks longer than the effect of free drug. After administration of both drug forms, the proliferative responses of T and B cells were restored, and also the number of CD4+ and CD8+ increased markedly. In lip.ABZ-treated mice, stimulation of mentioned lymphocyte parameters, except that of CD8+ numbers, persisted for longer period than after ABZ therapy, where values peaked at week 12 p.i., then declined more rapidly. A very strong stimulatory effect was seen on B lymphocytes during the period of lip.ABZ administration, although interestingly, numbers of CD8+ cells were higher in free ABZ-treated group. Low concentrations of IFN-γ (Th1 response) were present in infected, untreated mouse serum. Only moderate IFN-γ elevation was observed after treatment with free ABZ. A profound increase of its concentration was seen shortly after administration of lip.ABZ, and persisted until the experiment ended. In infected untreated mice, concentration of IL-5 (Th2 response) was highest on week 2 p.i. Significantly more IL-5 was recorded in serum of mice treated with free ABZ treatment than with lip.ABZ from week 12 to 18 p.i. (weeks 2–8 after the last dose). After the initial increase of superoxide anions (weeks 4–11 p.i.), generation of O₂⁻ by peritoneal macrophages was gradually inhibited by E. multilcoularis infection. In general, treatment abolished this suppression and macrophages from lip.ABZ-treated mice produced elevated amounts of O₂⁻ over a longer period than macrophages from ABZ-treated mice. Our data indicate that anthelmintic potency of ABZ could be increased after incorporation into liposomes, not only because of improved pharmacokinetics and consequent bioavailability, but also because of significant stimulation of Th1-type cytokine IFN-γ response and effector macrophage functions.     

The growth and nutrient utilization of the insect cell line Spodoptera frugiperda Sf9 in batch and continuous culture

The growth of the Spodoptera frugiperda cell line Sf9 was studied in batch and continuous culture. The results of batch cultivations showed that glucose was the preferred energy and carbon source limiting the cell density in both TNM-FH and IPL-41 media. Continuous culture using IPL-41-based feeding medium with different glucose (2.5, 5 and 10 g l⁻¹) and yeast extract concentrations (4, 8 and 16 g l⁻¹) showed that in serum-supplemented medium the maximum cell density was limited by glucose and yeast extract concentration. The transition to glucose limitation caused a decrease in growth rate and viability. A high cell density culture (18 × 10⁶ ml⁻¹) was obtained using a glucose concentration of 10 g l⁻¹ and a yeast extract concentration of 8 g l⁻¹ in the feeding medium. A yeast extract concentration of 16 g l⁻¹ inhibited growth. Unlike mammalian cell cultures, lactate, alanine and ammonia were not involved in growth inhibition. Lactate did not accumulate under aerobic conditions. Ammonia accumulation, if observed, was insignificant. The level of alanine synthesized and excreted into the culture medium never reached an inhibitory level. During glucose limitation alanine did not accumulate and ammonia was released. However, even in the presence of glucose significant amounts of Asp, Glu, Gln, Asn, Ser, Arg and Met were utilized for energy production. The amino groups of these amino acids were transferred to pyruvate or used for nucleic acid synthesis and excreted in the form of alanine into the culture medium. The consumption of His, Lys, Thr, Gly, Val, Leu, Phe, Tyr, Trp and Ile by growing Sf-9 cells was almost equal to their concentration in the biomass.     

Effect of oxygen transfer rate on levels of key enzymes of xylose metabolism in Debaryomyces hansenii

The titers of key enzymes of xylose metabolism were measured and correlated with the kinetics of xylitol production by Debaryomyces hansenii under different oxygen transfer rates (OTR) in a batch reactor. An OTR change from 2.72 to 4.22 mmol O₂ l⁻¹ min⁻¹ resulted in a decrease in NADPH-dependent xylose reductase (XR) and NAD ± -dependent xylitol dehydrogenase (XDH) activities. For higher values of OTR (12.93 mmol O₂ l⁻¹ min⁻¹, the XDH titer increased twofold whereas the XR titer did not show a significant change. At the lowest OTR (2.72 mmol O₂ l⁻¹ min⁻¹), xylitol (and ethanol) production rates showed the highest values. However, xylitol specific productivity was twice as high as ethanol specific productivity. The titer of the NADPH-forming enzyme, glucose-6-phosphate dehydrogenase (GPDH), increased from 333 to 412 mU mg⁻¹ when the OTR was increased. However, 6-phosphogluconate dehydrogenase (PGDH) activity remained unchanged and at a lower level, which indicates that this enzyme is responsible for the carbon flux control of the oxidative branch of the pentose phosphate pathway. The activity of the alcohol-forming enzyme was repressed at the higher amount of oxygen, decreasing its activity more than 50%. The changes in ADH suggested that two different metabolic regions under oxygen-limited conditions can be hypothesized for xylose metabolism by D. hansenii. For low OTR values (up to 4.22 mmol O₂ l⁻¹ min⁻¹), a fermentative-type activity is displayed. At higher OTR values (above 4.22 mmol O₂ l⁻¹ min⁻¹), no significant fermentative activity is reported.     

Continuous production of lactic acid from whey permeate by Lactobacillus helveticus in two chemostats in series

The effect of dilution rate on the production of lactic acid from whey permeate by Lactobacillus helveticus has been investigated. In the first chemostat of a two-stage system, total conversion (98.1%) and maximum lactic acid concentration (43.7 g l⁻¹) were obtained at a dilution rate (D_Itot) of 0.06 h⁻¹. Maximum volumetric productivities of lactic acid (8.27 g l⁻¹ h⁻¹) and biomass (1.90 g l⁻¹ h⁻¹) occurred at D_Itot of 0.40 h⁻¹. The fraction of -lactate in the product was found to increase with dilution rate and reached a maximum of 66% at the same dilution rate. The maximum specific growth rate (μ_max) on this medium was 0.7 h⁻¹. A Y_ATP (max) value of 22.4 g dry weight (mol ATP)⁻¹ and a maintenance coefficient of 8.0 mmol ATP (g dry weight h)⁻¹ were determined. The second stage, in series with the first, confirmed these results and further showed that the total residence time could be reduced by 50%, compared with a single chemostat for the same nearly complete level of substrate conversion.     

Determination of kinetic constants of hybrid textile wastewater treatment system

The present study is related to treatment of textile wastewater in microaerophilic–aerobic hybrid reactor. The study showed the effectiveness of biological treatment of wastewater involving appropriate microorganism and suitable reactors. COD and color were reduced to 82–94%, and 99% respectively for textile wastewater. The reactor was operated at highest loading of 16.4 g COD g l⁻¹ d⁻¹ and obtained 80% COD and 72% color removal. Biokinetic models were applied to data obtained from experimental studies in continuously operated hybrid reactor. Treatment efficiencies of the reactor were investigated at different hydraulic retention times (2.3–9.1 d) and organic loading rates (2.6–16.4 g COD l⁻¹ d⁻¹). Second-order and a Stover–Kincannon models were best fitted to the hybrid column reactor. The second-order substrate removal rate constant (k_2(S)) was found as 41.44 d⁻¹ for hybrid reactor. Applying the modified Stover–Kincannon model to the hybrid reactor, the maximum removal rate constant (U_max) and saturation value constant (K_B) were found to be 212 g l⁻¹ d⁻¹ and 22.89 g l⁻¹ d⁻¹, respectively.