Detection of intermediate metabolites of benzene biodegradation under microaerophilic conditions

The intermediate metabolites of benzene transformation by a microaerophilic bacterial consortium, adapted to degrade gasoline and benzene at low concentrations of dissolved oxygen (<1 mg l^-1), were identified. The examined range of initial DO concentration, 0.05 to 1 mg l^-1, was considerably lower than the previously reported values believed to be necessary to initiate benzene biodegradation. An extensive transformation of benzene, higher than the theoretical predictions for its aerobic oxidation, was observed. Phenol was identified as the most stable and the major intermediate metabolite which was subsequently transformed into catechol and benzoate. The use of ¹³C-labeled compounds identified benzene as the source of phenol, and phenol as the source of catechol and benzoate, suggesting the involvement of a monooxygenase enzymatic system in biodegradation of benzene at low DO concentrations. A metabolic sequence was proposed to describe the simultaneous detection of catechol and benzoate during the microaerophilic transformation of benzene. The results of this work demonstrate that it is possible to transform benzene, a highly carcinogenic hydrocarbon and a major contaminant of groundwater, to more easily biodegradable compounds in the presence of very small amounts of oxygen.     

Controlled Field Study on the Use of Nitrate and Oxygen for Bioremediation of a Gasoline Source Zone

Controlled releases of unleaded gasoline were used to evaluate the biotransformation of the soluble aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylene isomers, trimethylbenzene isomers, and naphthalene) within a source zone using nitrate and oxygen as electron acceptors. Experiments were performed within two 2 m×2 m×3.5 m deep sheet-piling cells. A gasoline-contaminated zone was created below the water table in each treatment cell. Groundwater amended with electron acceptors was then flushed continuously through the cells for 174 d. One cell received approximately 100 mg/L nitrate and “microaerophilic” (i.e., 2 mg/L or less) dissolved oxygen (DO), a second cell received micro aerophilic DO only. Electron-acceptor utilization and hydrocarbon-metabolite formation were observed in both cells, suggesting that some microbial activity had been induced in response to flushing. However, nitrate utilization was slow relative to the cell residence time, and aromatic-hydrocarbon mass losses in response to microaerophilic DO addition were not apparent under these in situ conditions. Concentration trends in both cells suggested that there was relatively little biotransformation of the aromatic hydrocarbons over the 2-m flow path monitored in this experiment. Extraction-well concentration trends, for example, were consistent with abiotic gasoline dissolution. The results from the nitrate-amended cell suggest that a large denitrifying population capable of aromatic hydrocarbon biotransformation failed to develop within the gasoline source zone over a 14-month period of nitrate exposure. This study reinforces the need for detailed aquifer-specific testing prior to selecting bioremediation for full-scale cleanup, particularly for recent hydrocarbon spills.     

以纸为碳源去除地下水硝酸盐的研究

研究了以纸为碳源和反应介质的生物反应器对水中硝酸盐的去除。结果表明,以纸为碳源的反应器启动快．反硝化反应受温度及水力停留时间影响大。25℃的反硝化速率是14℃的1．7倍。在室温25±1℃,进水硝酸盐氮浓度为45．2mg·L^-1、水力停留时间8．6h时,反应器对硝酸盐氮的去除率在99．6％以上,当水力停留时间为7．2h,氮去除率只有50％。反硝化反应受pH值和溶解氧的影响小,反应进行过程中,纸表面形成了生物膜,纸也被消耗了．采用反应器出水再经活性炭吸附的工艺流程处理高硝酸盐氮地下水,<33．9mg·L^-1的硝酸盐氮完全去除,没有出现NC2-N,最终出水水质DOC<11mg·L^-1。     

Influence of oxygen on the growth of Saccharomyces cerevisiae in continuous culture

Baker's yeast, Saccharomyces cerevisiae, was investigated for the combined influence of dissolved oxygen and glucose concentration in continuous culture. A reactor was operated at a range of dilution rates (0.1, 0.2, 0.25, 0.27, and 3.0 h(-1)), above and below the critical value that separates the oxidative and fermentation regions. For each dilution rate (D), steady states were established at each of five to ten different dissolved oxygen concentrations (DO) in the range of 0.01-5 mg/L. The use of on-line mass spectrometry facilitated the measurement of gaseous and dissolved O(2), CO(2), and ethanol. Intracellular carbohydrate, protein, RNA, DNA, lipid, and cytochrome concentrations were measured. Cell size measurements were reduced to specific surface areas. Cytochrome content showed up to 100% variation during a 20-day period of adaptation at D = 0.2 h(-1) to low DO. Eventually, the culture behaved the same at DO = 0.05 mg/L as it did initially at 3 mg/L. At D = 0.2, 0.25, and 0.27 h(-1), the transition between oxidation and fermentation was characterized by a critical DO which decreased with decreasing D. The X-D curves were shifted such that the critical D value was reduced with decreasing DO. Specific oxygen update rates varied with DO according to the saturation kinetics. Specific cell surface areas increased with decreasing DO. Cytochrome content generally decreased with decreasing DO, and Q(O(2) ) could be linearly related to the total cytochrome content, which exhibited a maximum at D = 0.27 h(-1).     

Benzene transformation in nitrifying batch cultures

The effect of benzene on the nitrifying activity of a sludge produced in steady-state nitrification was evaluated in batch cultures. Benzene at 10 mg/L inhibited nitrate formation by 53%, whereas at 5 mg/L there was no inhibition. For initial benzene concentrations of 0, 7, and 10 mg/L, the specific rates of NO(3)(-)-N production were 0.545 +/- 0.101, 0.306 +/- 0.024, and 0.141 +/- 0.010 g NO(3)(-)-N/g microbial protein-N.h, respectively. The specific rates of benzene consumption at 7, 12, and 20 mg/L were 0.034 +/- 0.003, 0.050 +/- 0.006, and 0.027 +/- 0.002 g/g microbial protein-N.h, respectively. Up to a concentration of 10 mg/L, benzene was first oxidized to phenol, which was later totally oxidized to acetate. Benzene at higher concentrations (20 and 30 mg/L) was converted to intermediates other than acetate, phenol, or catechol. These results suggest that this type of nitrifying consortium coupled with a denitrification system may have promising applications for complete removal of nitrogen and benzene from wastewaters.     

Processes impacting on benzene removal in vertical-flow constructed wetlands

The overall aim of this research project was to reduce low molecular weight hydrocarbons such as benzene in produced wastewaters. Over 30 months of research was conducted to test the treatment performance in terms of benzene removal in vertical-flow constructed wetlands. Based on an influent concentration of 1 g L(-1) benzene, the results show mean benzene removal efficiencies between 88.71% and 89.77%, and 72.66% and 80.46% for indoor and outdoor constructed wetlands, respectively. A statistical analysis indicated that the five days at 20 degrees C N-allylthiourea biochemical oxygen demand (BOD(5)), chemical oxygen demand (COD), nitrate-nitrogen (NO(3)-N), dissolved oxygen (DO) and electric conductivity (EC) values of the effluent were positively correlated with the effluent benzene concentrations following the order COD>DO>EC>NO(3)-N>BOD(5), and negatively correlated according to the order pH>redox potential (redox)>temperature (T)>turbidity. No strong relationships between benzene and the variables ortho-phosphate-phosphorus (PO(4)(3-)) and ammonia-nitrogen (NH(4)-N) were recorded.     

Determination of external and internal mass transfer limitation in nitrifying microbial aggregates

In this article we present a study of the effects of external and internal mass transfer limitation of oxygen in a nitrifying system. The oxygen uptake rates (OUR) were measured on both a macro-scale with a respirometric reactor using off-gas analysis (Titrimetric and Off-Gas Analysis (TOGA) sensor) and on a micro-scale with microsensors. These two methods provide independent, accurate measurements of the reaction rates and concentration profiles around and in the granules. The TOGA sensor and microsensor measurements showed a significant external mass transfer effect at low dissolved oxygen (DO) concentrations in the bulk liquid while it was insignificant at higher DO concentrations. The oxygen distribution with anaerobic or anoxic conditions in the center clearly shows major mass transfer limitation in the aggregate interior. The large drop in DO concentration of 22-80% between the bulk liquid and aggregate surface demonstrates that the external mass transfer resistance is also highly important. The maximum OUR even for floccular biomass was only attained at much higher DO concentrations (approximately 8 mg/L) than typically used in such systems. For granules, the DO required for maximal activity was estimated to be >20 mg/L, clearly indicating the effects of the major external and internal mass transfer limitations on the overall biomass activity. Smaller aggregates had a larger volumetric OUR indicating that the granules may have a lower activity in the interior part of the aggregate.     

Biodegradation of Benzene in a Laboratory-Scale Biobarrier at Low Dissolved Oxygen Concentrations

A laboratory-scale permeable biobarrier exhibited high removal efficiencies of benzene at inlet concentrations of 0.4 to 35.1?mg/L and with a limited supply of dissolved oxygen. The supplied oxygen was less than the demand for a complete aerobic oxidation of benzene. Stainless steel pieces or granulated peat moss were used as packing material for microbial support in the biobarrier. Removal efficiencies ranged from 63.9% to 99.9% in the stainless steel-packed biobarrier and from 70.4% to 97.2% in the peat moss-packed biobarrier, while benzene elimination rate changed from 0.2 to 10.4?mg/L-d and from 0.1 to 3.7?mg/L-d in the two biobarriers, respectively. The consumption of sulfate and the presence of sulfate-reducing bacteria suggested the contribution of anaerobic metabolism in the biodegradation of benzene. The biodegradation of benzene under microaerophilic conditions (defined as dissolved oxygen concentrations <2?mg/L) was demonstrated during independent batch experiments. The maximum specific rate of benzene biodegradation with concentrations of 22.0 to 65.9?mg/L under microaero-philic conditions was 2.6 mg/mg biomass-d.     

Hyperproduction of cordycepin by two-stage dissolved oxygen control in submerged cultivation of medicinal mushroom Cordyceps militaris in bioreactors

Effect of oxygen supply on cordycepin production was investigated in submerged cultivation of Cordyceps militaris, a famous traditional Chinese medicinal mushroom, in a 5-L turbine-agitated bioreactor (TAB). Initial volumetric oxygen transfer coefficient (kLa) within the range of 11.5-113.8 h(-1) had significant influence on cordycepin production. The highest cordycepin concentration of 167.5 mg/L was obtained at an initial kLa value of 54.5 h(-1), where a moderate dissolved oxygen (DO) pattern was observed throughout cultivation. The possible correlation between cordycepin production and DO level was explored by DO control experiments, and the results showed that DO within the range of 10-80% of air saturation greatly affected the cultivation process. To obtain a high specific cordycepin formation rate (rho) throughout cultivation, a two-stage DO control strategy was developed based on the analysis of the relationship of rho and DO. That is, DO was controlled at 60% from the beginning of cultivation and then shifted to a lower control level of 30% when rho started to decrease. As a result, a high cordycepin production of 201.1 mg/L and a high productivity of 15.5 mg/(L.d) were achieved, which was enhanced by about 15% and 30% compared to the highest titers obtained in conventional DO control experiments, respectively. The proposed DO control strategy was also applied to a recently developed 5-L centrifugal impeller bioreactor (CIB) with cordycepin production and productivity titers of 188.3 mg/L and 14.5 mg/(L.d). Furthermore, the scale-up of the two-stage DO control process from 5-L CIB to 30-L CIB was successfully demonstrated. The work is useful for the efficient large-scale production of bioactive metabolites by mushroom cultures.     

Mechanistic changes during phytoremediation of perchlorate under different root-zone conditions

Two types of hydroponic bioreactors were used to investigate the mechanisnistic changes during phytoremediation of perchlorate under different root-zone conditions. The bioreactors included: (1) an aerobic ebb-and-flow system planted with six willow trees, and (2) individual willow trees grown in sealed root-zone bioreactors. Rhizosphere probes were used to monitor for the first time during phytoremediation of perchlorate, diurnal swings in oxidation-reduction potential (E(H)), dissolved oxygen (DO), and pH. Radiolabeled (36Cl-labeled) perchlorate was used as a tracer in a subset of the sealed bioreactor experiments to quantify the contribution of phytodegradation and rhizodegradation mechanisms. Rhizodegradation accounted for the removal of 96.1 +/- 4.5% (+/-95% CI) of the initial perchlorate dose in experiments conducted in sealed hydroponic bioreactors with low DO and little or no nitrate N. Meanwhile, the contribution of rhizodegradation decreased to 76 +/- 14% (+/-95% CI) when nitrate (a competing terminal electron acceptor) was provided as the nitrogen source. Slower rates of phytoremediation by uptake and phytodegradation were observed under high nitrate concentrations and aerobic conditions, which allowed perchlorate to persist in solution and resulted in a higher fraction uptake by the plant. Specifically, the rate of removal of perchlorate from bulk solution ranged from 5.4 +/- 0.54 to 37.1 +/- 2.25 mg/L/d (+/-SE) in the absence of nitrate to 1.78 +/- 0.27 to 0.46 +/- 0.02 mg/L/d (+/-SE) at high nitrate concentration. The results of this study indicate that the root-zone environment of plants can be manipulated to optimize rhizodegradation and to minimize undesirable processes such as uptake, temporal phytoaccumulation, and slow phytodegradation during phytoremediation of perchlorate. Rhizodegradation is desired because contaminants resident in plant tissue may remain an ecological risk until completely phytodegraded.     

Removal of carbamazepine and sulfamethoxazole by MBR under anoxic and aerobic conditions

This study reveals for the first time that near-anoxic conditions (dissolved oxygen, DO=0.5 mg/L) can be a favorable operating regime for the removal of the persistent micropollutant carbamazepine by MBR treatment. The removal efficiencies of carbamazepine and sulfamethoxazole by an MBR were systematically examined and compared under near-anoxic (DO=0.5 mg/L) and aerobic (DO>2 mg/L) conditions. Preliminary batch tests confirmed that sulfamethoxazole is amenable to both aerobic and anoxic biotransformation. However, carbamazepine-a known persistent compound-showed degradation only under an anoxic environment. In good agreement with the batch tests, during near-anoxic operation, under a high loading of 750 μg/Ld, an exceptionally high removal (68±10%) of carbamazepine was achieved. In contrast, low removal efficiency (12±11%) of carbamazepine was observed during operation under aerobic conditions. On the other hand, an average removal efficiency of 65% of sulfamethoxazole was achieved irrespective of the DO concentrations.     

UASB/Flash aeration enable complete treatment of municipal wastewater for reuse

A simple, efficient and cost-effective method for municipal wastewater treatment is examined in this paper. The municipal wastewater is treated using an upflow anaerobic sludge bed (UASB) reactor followed by flash aeration (FA) as the post-treatment, without implementing aerobic biological processes. The UASB reactor was operated without recycle, at hydraulic retention time (HRT) of 8 h and achieved consistent removal of BOD, COD and TSS of 60-70% for more than 12 months. The effect of FA on UASB effluent post-treatment was studied at different HRT (15, 30 and 60 min) and dissolved oxygen (DO) concentrations (low DO = 1-2 mg/L and high DO = 5-6 mg/L). The optimum conditions for BOD, COD and sulfide removal were 30-60 min HRT and high DO concentration inside the FA tank. The final effluent after clarification was characterized by BOD and COD values of 28-35 and 50-58 mg/L, respectively. Sulfides were removed by more than 80%, but the fecal coliform only by ~2 log. The UASB followed by FA is a simple and efficient process for municipal wastewater treatment, except for fecal coliform, enabling water and nutrients recycling to agriculture.     

The effect of dissolved oxygen and aeration rate on antibiotic production of Streptomyces fradiae

Different dissolved oxygen concentrations and aeration rates were imposed on a stable mutant of Streptomyces fradiae during the antibiotic-producing phase. At high aeration rate (1 vvm), the tylosin yield in the fermentor broth with dissolved oxygen (DO) concentrations controlled close to 100% saturation (6-8 ppm) increased 10% as against uncontrolled. The rates of cellular growth, oil consumption, and tylosin production were severely reduced when DO concentration fell below 25% saturation, but all resumed to their initial rates when DO was raised to saturation level again. The DO concentration in combination with air flow rate affected the pattern of the antibiotics produced. At high DO levels, an additional macrolide antibiotic, macrocin, was synthesized to more than one-third the amount of tylosin at high aeration rate (1 vvm). On the other hand, tylosin production rate remained constant and no significant amount of macrocin was produced at low aeration rate (0.2 vvm).     

Uptake and biotransformation of 2,4,6-trinitrotoluene (TNT) by microplantlet suspension culture of the marine red macroalga Portieria hornemannii

Microplantlets of the marine red macroalga Portieria hornemannii efficiently removed the explosive compound 2,4,6-trinitrotoluene (TNT) from seawater. Photosynthetic, axenic microplantlets (1.2 g FW/L) were challenged with enriched seawater medium containing dissolved TNT at concentrations of 1.0, 10, and 50 mg/L. At 22 degrees C and initial TNT concentrations of 10 mg/L or less, TNT removal from seawater was 100% within 72 h, and the first-order rate constant for TNT removal ranged from 0.025 to 0.037 L/gFW h under both illuminated conditions (153 microE/m(2)s, 14:10 LD photoperiod) and dark conditions. Two immediate products of TNT biotransformation, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dintrotoluene, were identified in the liquid culture medium, with a maximum material balance recovery of 29 mole%. Only trace levels of these products and residual TNT were found within the fresh cell biomass. Removal of TNT by P. hornemannii microplantlets at initial concentrations of 1.0 or 10 mg/L did not affect the respiration rate. At an initial TNT concentration of 10 mg/L, net photosynthesis decreased towards zero, commensurate with the removal of dissolved TNT from seawater, whereas at an initial TNT concentration of 1.0 mg/L, the net photosynthesis rate was not affected.     

Effects of increased phosphorus loading on dissolved oxygen in a subtropical wetland, the Florida Everglades

The Florida Everglades is an oligotrophic, phosphorus (P)-limited wetland that is experiencing eutrophication as a result of P-enriched agricultural runoff. Effects of P enrichment on diel water-column dissolved oxygen concentration (DO) profiles were measured along nutrient gradients downstream of agricultural discharges in two northern Everglades marshes and in field enclosures (mesocosms) exposed to different P loading rates. Reference (i.e., water-column TP < 10 g/L) areas in the marsh interior were characterized by strong diel fluctuations in DO, and aerobic conditions generally were maintained throughout the diel cycle. Enriched stations (water-column TP elevated to between 12 and 131 g/L) were characterized by dampened diel fluctuations and reduced DO, and the extent of these changes was correlated strongly with marsh P concentrations. Mean DO declined from between 1.81 and 7.52 mg/L at reference stations to between 0.04 and 3.18 mg/L in highly enriched areas. Similarly, minimum DO declined from between 0.33 and 5.86 mg/L to between 0 and 0.84 mg/L with increasing enrichment, and the frequency of extremely low DO (< 1 mg/L) increased from between 0 and 20% to as high as 100% in the most enriched areas. Diel oxygen profiles in P-enriched mesocosms declined progressively with time; all loading treatments exhibited similar DO during the 1^st year of P loading, but concentrations declined significantly at higher loads by year 3. Reductions in water-column DO with increased P enrichment were associated with reduced oxygen production by submersed periphyton and macrophytes and increased sediment oxygen demand. Increased emergent macrophyte cover in enriched areas likely contributed to these changes by shading the water-column, which inhibited submerged productivity, and by providing inputs of nutrient-rich detritus, which increased oxygen demand. Declines in marsh DO are associated with other ecological changes such as increased anaerobic metabolism and an increase in invertebrate taxa that tolerate low DO. While background oxygen concentrations in wetlands can be lower than those in lakes and rivers, declines in water-column DO caused by eutrophication can result in biological impacts similar to those in other aquatic ecosystems.     

Long term hypoxia suppresses reproductive capacity in the estuarine fish, Fundulus grandis

Human nutrient input has significantly altered dissolved oxygen (DO) cycles in coastal waters such that summertime hypoxia (DO <2 mg/L) and anoxia of bottom water are common worldwide. Prolonged hypoxia usually reduces metabolic rate in fish and potentially reduces reproduction, particularly in a spring and summer spawning species such as the Gulf killifish, Fundulus grandis. To evaluate the effects of long term hypoxia on reproduction, Gulf killifish were subjected to either normoxia (6.68+/-2.1 mg/L DO) or hypoxia (1.34+/-0.45 mg/L DO) for one month. Fecundity, growth, gonadosomatic index (GSI), circulating sex steroids (testosterone, T; 11-ketotestosterone, 11KT; and estradiol-17beta, E2), and egg yolk protein (vitellogenin, VTG) were measured. Hypoxia significantly reduced growth and reproduction. E2 was 50% lower in females and 11KT was 50% lower in males, although the precursor hormone T was unchanged in either sex after hypoxic exposure. Hypoxia-exposed females produced significantly fewer eggs and initiated spawning later than control fish. Plasma VTG concentration was unchanged, suggesting that hypoxia may delay VTG uptake by oocytes. Long term laboratory exposure clearly suppressed reproductive capacity in Gulf killifish. Wild populations experience cyclic hypoxia which could have equivalent effects if daily hypoxic periods are long and frequent - a potential consequence of anthropogenic nutrient enrichment in marsh systems.     

Enhanced anaerobic biodegradation of BTEX-ethanol mixtures in aquifer columns amended with sulfate,chelated ferric iron or nitrate

Flow-through aquifer columns were used to investigate the feasibility of adding sulfate, EDTA–Fe(III) or nitrate to enhance the biodegradation of BTEX and ethanol mixtures. The rapid biodegradation of ethanol near the inlet depleted the influent dissolved oxygen (8 mg l^-1), stimulated methanogenesis, and decreased BTEX biodegradation efficiencies from >99% in the absence of ethanol to an average of 32% for benzene, 49% for toluene, 77% for ethylbenzene, and about 30% for xylenes. The addition of sulfate, EDTA–Fe(III) or nitrate suppressed methanogenesis and significantly increased BTEX biodegradation efficiencies. Nevertheless, occasional clogging was experienced by the column augmented with EDTA–Fe(III) due to iron precipitation. Enhanced benzene biodegradation (>70% in all biostimulated columns) is noteworthy because benzene is often recalcitrant under anaerobic conditions. Influent dissolved oxygen apparently played a critical role because no significant benzene biotransformation was observed after oxygen was purged out of the influent media. The addition of anaerobic electron acceptors could enhance BTEX biodegradation not only by facilitating their anaerobic biodegradation but also by accelerating the mineralization of ethanol or other substrates that are labile under anaerobic conditions. This would alleviate the biochemical oxygen demand (BOD) and increase the likelihood that entraining oxygen would be used for the biotransformation of residual BTEX.     

溶氧水平对红豆杉细胞悬浮培养的影响研究

紫杉醇 (Ｔａｘｏｌ)是源自红豆杉提取物的一种高度衍生化的二萜类化合物 ,临床实验结果表明紫杉醇对于卵巢癌、乳腺癌、胃肠道癌等具有明显的抗肿瘤活性[1] ,因而受到世界各国的广泛关注 ,并已被美国食品与药品管理局 (ＦＤＡ)批准用于卵巢癌与乳腺癌的治疗[2 ] 。到目前为止紫杉醇仍然主要从树皮中提取 ,但由于红豆杉生长缓慢 ,天然资源非常有限 ,加快其替代来源的研究势在必行。利用植物细胞悬浮培养生产紫杉醇作为一种可行的选择 ,近年来取得了较大的进展[3 ,4 ] 。本文研究了摇瓶及 2 0 Ｌ反应器培养过程的溶氧水平对细胞生长及紫杉醇…     

Design of a system for the control of low dissolved oxygen concentrations: critical oxygen concentrations for Azotobacter vinelandii and Escherichia coli

The physiological activity of microorganisms in environments with low dissolved oxygen concentrations often differs from the metabolic activity of the same cells growing under fully aerobic or anaerobic conditions. This article describes a laboratory-scale system for the control of dissolved oxygen at low levels while maintaining other parameters, such as agitator speed, gas flowrate, position of sparger outlet, and temperature at fixed values. Thus, it is possible to attribute in dilute nonviscous fermentations all physiologic changes solely to changes in dissolved oxygen. Experiments were conducted with Azotobacter vinelandii and Escherichia coli. Critical oxygen concentrations for growth (that value of oxygen allowing growth at 97% of mu max) were measured as 0.35 +/- 0.03 mg/L for A. vinelandii and 0.12 +/- 0.03 mg/L for E. coli. These values are significantly different from the commonly quoted values for critical oxygen concentrations based on respiration rates. Because of the superior dissolved oxygen control system and an improved experimental protocol preventing CO2 limitation, we believe that the values reported in this work more closely represent reality.     

Effects of Partial O(2) Pressure, Partial CO(2) Pressure, and Agitation on Growth Kinetics of Azospirillum lipoferum under Fermentor Conditions

Azospirillum lipoferum crt1 was grown in batch cultures under standard conditions at 85% saturation of dissolved oxygen (DO) and 30-g/liter glucose concentrations. Kinetic studies revealed nutritional limitations of growth and the presence of an initial lag phase prior to consumption of glucose. The influences of various gaseous environments and shear stress on growth, i.e., various conditions of agitation-aeration, were characterized. Faster growth in the first stages of the culture and shorter duration of the lag phase were observed at DO concentrations of <30% saturation. The possible influences of dissolved CO(2) concentration or shear stress or both were discounted, and we confirmed the detrimental effect of high DO levels (up to 80% saturation) and the favorable influence of low DO concentrations (lower than 30% saturation) on growth. It was concluded that the gaseous environment, i.e., the DO concentration, needs to be considered as an operating parameter and be accurately controlled to ensure optimal growth of Azospirillum cells.