Aerobic and Anaerobic Bacterial and Fungal Degradation of Pyrene: Mechanism Pathway Including Biochemical Reaction and Catabolic Genes

Microbial biodegradation is one of the acceptable technologies to remediate and control the pollution by polycyclic aromatic hydrocarbon (PAH). Several bacteria, fungi, and cyanobacteria strains have been isolated and used for bioremediation purpose. This review paper is intended to provide key information on the various steps and actors involved in the bacterial and fungal aerobic and anaerobic degradation of pyrene, a high molecular weight PAH, including catabolic genes and enzymes, in order to expand our understanding on pyrene degradation. The aerobic degradation pathway by Mycobacterium vanbaalenii PRY-1 and Mycobactetrium sp. KMS and the anaerobic one, by the facultative bacteria anaerobe Pseudomonas sp. JP1 and Klebsiella sp. LZ6 are reviewed and presented, to describe the complete and integrated degradation mechanism pathway of pyrene. The different microbial strains with the ability to degrade pyrene are listed, and the degradation of pyrene by consortium is also discussed. The future studies on the anaerobic degradation of pyrene would be a great initiative to understand and address the degradation mechanism pathway, since, although some strains are identified to degrade pyrene in reduced or total absence of oxygen, the degradation pathway of more than 90% remains unclear and incomplete. Additionally, the present review recommends the use of the combination of various strains of anaerobic fungi and a fungi consortium and anaerobic bacteria to achieve maximum efficiency of the pyrene biodegradation mechanism.     

Enhanced bioremediation of crude oil‐contaminated soil by a Pseudomonas species and mutually associated adapted Azotobacter vinelandii

A mixed culture of compatible hydrocarbonoclastic and diazotrophic bacteria, each at a density of 10⁸ organisms cm^?3, was developed for optimised bioremediation of crude oil‐contaminated soil. The hydrocarbonoclastic bacterium, Pseudomonas sp and the diazotroph, Azotobacter vinelandii, were both isolated from a previously crude oil‐contaminated soil and thereafter modelled as a unit of mutualistic consortium in situ. Stabilisation of the consortium and hence the optimised bioremediation process occurred when the bacterial growth attained a pseudo‐steady state condition. This was considered to be as a result of a symbiotic association between A vinelandii and the Pseudomonas sp in which A vinelandii produced the required concentration of fixed nitrogen compounds required for the growth of the Pseudomonas sp. Enhancement in biodegradation, due to stimulated growth of Pseudomonas sp and co‐metabolic activity of A vinelandii, was mathematically evaluated as the difference in the specific growth rates (µ) between the consortium Pseudomonas sp/A vinelandii and Pseudomonas sp alone. The proportion of petroleum hydrocarbons degraded by the consortium from the contaminated soil ranged between 66.83 and 69.6% as compared with that of a pure culture of Pseudomonas sp (23.2–44.45%). Hence, beyond their role in biological nitrogen fixation, diazotrophs may be used to contribute to bioremediation of crude oil‐contaminated land. Copyright © 2004 Society of Chemical Industry     

Genome‐scale modeling of Synechocystis sp. PCC 6803 and prediction of pathway insertion

BACKGROUND: Cyanobacterium Synechocystis sp. PCC 6803 has been used widely as a model system for the study of photosynthetic organisms and higher plants. The aim of this work was to integrate the genomic information, biochemistry and physiological information available for Synechocystis sp. PCC 6803 to reconstruct a metabolic network for system biology investigations. RESULTS: A genome‐scale Synechocystis sp. PCC 6803 metabolic network, including 633 genes, 704 metabolites and 831 metabolic reactions, was reconstructed for the study of optimal Synechocystis growth, network capacity and functions. Heterotrophic, photoautotrophic and mixotrophic growth conditions were simulated. The Synechocystis model was used for in silico predictions for the insertion of ethanol fermentation pathway, which is a novel approach for bioenergy and biofuels production developed in the authors' laboratory. Simulations of Synechocystis cell growth and ethanol production were compared with actual metabolic measurements which showed a satisfactory agreement. CONCLUSION: The Synechocystis metabolic network developed in this study is the first genome‐scale mathematical model for photosynthetic organisms. The model may be used not only in global understanding of cellular metabolism and photosynthesis, but also in designing metabolic engineering strategies for desirable bio‐products. Copyright © 2008 Society of Chemical Industry     

Biodegradation Capability and Enzymatic Variation of Potentially Hazardous Polycyclic Aromatic Hydrocarbons—Anthracene and Pyrene by Anabaena fertilissima

This study encompasses the biodegradation capacity of Anabaena fertilissima to model PAH (Polycyclic Aromatic Hydrocarbon) compounds namely Anthracene (ANT) and Pyrene (PYR) at different LC₅₀ concentrations viz., 5.0 mg/L and 3.0 mg/L, respectively, on growth in terms of Chlorophyll-a and protein. Depletion in chlorophyll-a and protein content was registered with rise in PAHs concentration while the inhibition of nitrogen fixing enzymes such as nitrate reductase and glutamine synthetase activity was also concentration dependent and showed more sensitivity for high molecular weight aromatic compound PYR as compared to ANT. GC/MS analysis explained the degradation of ANT by 46% and PYR by 33%, at 5.0 mg/L and 3.0 mg/L, respectively. Moreover, the common degraded product for ANT was 2, 4-Dimethyl-1-heptene and for PYR it was 2, 3, 4-Trimethylhexane. Results indicate that PYR was more stable and recalcitrant compared to ANT. This study suggests that Anabaena fertilissima could be used for bioremediation of ANT and PYR pollution in surface waters and terrestrial environments.     

The Synechocystis sp. PCC6803 Sfp‐Type Phosphopantetheinyl Transferase Does Not Possess Characteristic Broad‐Range Activity

The cyanobacterium Synechocystis sp. PCC6803 harbours one phosphopantetheinyl transferase (PPTase), Sppt. Protein modelling supported previous bioinformatics analyses, which suggested that Sppt is a Sfp‐type PPTase with the potential to phosphopantetheinylate a broad range of carrier proteins from both primary and secondary metabolism. However, no natural products are synthesised by this species, which raises interesting evolutionary and functional questions. Phosphopantetheinylation assays and kinetic data demonstrate that Sppt was able to activate its cognate fatty acid synthesis carrier protein, SACP, but was unable to effectively activate various cyanobacterial carrier proteins from secondary metabolism or glycolipid biosynthesis pathways. To our knowledge, this is the first example of a PPTase with a Sfp‐type structure, but with activity more closely resembling AcpS‐type enzymes. The broad‐range PPTase from Nodularia spumigena NSOR10 was introduced into Synechocystis sp. PCC6803 and was shown to activate a noncognate carrier protein, in vivo. This engineered strain could provide a future biotechnological platform for the heterologous expression of cyanobacterial biosynthetic gene clusters.     

Biosurfactant-Assisted Bioremediation of Polycyclic Aromatic Hydrocarbons (PAHs) in Liquid Culture System and Substrate Interactions

A lipopeptide biosurfactant was produced by the bacterium Pseudomonas aeruginosa strain LBP9 isolated from petroleum-contaminated soil. Phenanthrene, fluoranthene, and pyrene were used as model polycyclic aromatic hydrocarbons (PAHs) to study the effect of the biosurfactant on the biodegradation of mixed and sole substrate PAHs, and examine substrate interactivity effects on their biodegradation in liquid culture. At 400 mg/L amendment of lipopeptide, the solubility of phenanthrene, fluoranthene, and pyrene were increased to 19, 33, and 45 times their aqueous solubility, respectively, and the extent of substrate utilization rate (q_max?) of PAHs was enhanced up to three-fold in the sole substrate studies in comparison to the unamended controls. In the ternary PAH mixture at total concentration of 300 mg/L, with equal parts of each PAH, 77%, 57%, and 33% degradation of phenanthrene, fluoranthene, and pyrene were observed, respectively, at 400 mg/L lipopeptide amendment on day 30 of incubation. Whereas in the sole substrate experiments at 300 mg/L concentration of each PAH and the same level of lipopeptide amendment more than 98% fluoranthene and 76% pyrene were degraded and phenanthrene removal was so rapid that at day 4 of incubation more than 80% was degraded. Biosurfactants at optimum amounts enhanced biodegradation of PAHs. Lipopeptide amendments of 200 mg/L and 400 mg/L were found out to be optimum amounts for statistically significant (p < 0.05) biodegradation of the PAHs in the experiments. However, despite biosurfactant-enhanced bioavailability of the PAHs, biodegradation rate was competitively inhibited in the multisubstrate microcosms.     

Oil production by a consortium of oleaginous microorganisms grown on primary effluent wastewater

BACKGROUND: Municipal wastewater could be a potential growth medium that has not been considered for cultivating oleaginous microorganisms. This study is designed to determine if a consortium of oleaginous microorganism can successfully compete for carbon and other nutrients with the indigenous microorganisms contained in primary effluent wastewater. RESULTS: The oleaginous consortium inoculated with indigenous microorganisms reached stationary phase within 24 h, reaching a maximum cell concentration of 0.58 g L^?1. Water quality post‐oleaginous consortium growth reached a maximum chemical oxygen demand (COD) reduction of approximately 81%, supporting the consumption of the glucose within 8 h. The oleaginous consortium increased the amount of oil produced per gram by 13% compared with indigenous microorganisms in raw wastewater. Quantitative polymerase chain reaction (qPCR) results show a substantial population increase in bacteria within the first 24 h when the consortium is inoculated into raw wastewater. CONCLUSION: This result, along with the fatty acid methyl esters (FAMEs) results, suggests that conditions tested were not sufficient for the oleaginous consortium to compete with the indigenous microorganisms. Copyright © 2010 Society of Chemical Industry     

Cost-cutting of nitrogen source for economical production of cellulolytic enzymes by Trichoderma inhamatum KSJ1

For saccharifying food wastes, cellulolytic enzymes were produced using Trichoderma inhamatum KSJ1 in modified Mandel’s medium. In a previous study, 0.1% bacto peptone in Mandel’s medium was established as the best organic nitrogen source for the production of cellulolytic enzymes using strain KSJ1. However, economically, peptone was too expensive. Therefore, soybean, yeast and Chunggookjang (fermented soybean paste) were substituted for peptone in this research. Also, yeast or ground soybean hydrolyzed by sulfuric acid or from a culture broth of Bacillus alcalophilus, a strain producing protease, was added to the medium as the nitrogen source to the production of cellulolytic enzyme. In the cultivation using 0.5% yeast hydrolyzed with a culture solution of B. alcalophilus as the nitrogen source, the activities of FPase and amylase were 0.20 and 2.17 U/mL in a 100 mL flask, compared to 0.35 and 1.24 U/mL with the 0.1% peptone as control, respectively. In a 10 L jar fermenter, the activities of FPase and amylase were improved to 0.40 and 4.82 U/mL in the cultivation, respectively, using 0.5% yeast hydrolyzed with the culture broth, compared with 0.38 and 3.79 U/mL, respectively, for the 0.1% peptone as control. Therefore, hydrolyzed yeast was established as an available nitrogen source for the industrial scale production of cellulolytic enzymes by strain KSJ1, resulting in a 52.3% cost reduction in the production of cellulolytic enzyme by substitution of the expensive nitrogen sources.     

Interactions between an alga and three bacterial species in a consortium selected for photosynthetic biomass and starch production

A four-membered consortium (MA003) of an algal species and bacteria was selected from a natural source for its ability to grow at 37°C and produce starch photosynthetically from carbon dioxide. The photosynthetic culture consisted of a Chlorella-like green alga (A003) and three heterotrophic bacteria, Alcaligenes sp. (B001), Flavobacter sp. (B002) and Serratia sp. (B003). The substrates for the bacterial growth were probably organic nitrogen and carbon compounds excreted by the alga at specific rates which were independent of the algal specific growth rate. The maximum specific growth rate of the alga was decreased by an inhibitor produced by bacterium B002. Bacterium B001 removed the inhibitor of algal growth released by bacterium B002, and bacterium B003 decreased the growth of bacterium B002 and consequently the production of algal growth inhibitor. The growth of bacterium B003 was greatly suppressed in the four-member consortium MA003. The coexisting bacteria in toto, did not affect the growth rate, yield and starch production of the algal member, but did help to establish a stable ecosystem and increase the biomass available. A culture density up to 36 g dry weight dm^?3 was achieved without significant variation in the ratio of the species in the culture.     

Applicability of Activated Carbon to Treatment of Waste Containing Iodine-Labeled Compounds

Abstract

A timber industry waste was transformed to activated carbon by a one-step chemical activation process using H₃PO₄ (H). The used activated carbon (SDH) was characterized by N₂ adsorption, FTIR, density, pH, point of zero charge pH_pzc, moisture and ash content. Methylene blue (MB) and the iodine number were calculated by adsorption from the solution. The applicability of the different activated carbon produced was carried out to treatment of aqueous waste contaminated with iodine-labeled prolactin (I-PRL) Treatment processes were performed under the varying conditions; contact time, temperature, carbon type, carbon dosage, and different particle size of the activated carbon (SDH). The results indicated that 5 hours are sufficient to reach a plateau, and the amount of I-PRL adsorbed on SDH activated carbons increase with the solution temperature with thermodynamic parameter of ΔG° = ?7.962 (kJ/mol), ΔH° = 28.869 (kJ/mol) and ΔS° = 109.94 (J/mol K). The optimum adsorption results were reached using carbon dose of 0.1 gm with particle size of <0.25 mm, and a batch factor (V/M) of 7.14 mlg^?1. First- and second-order equations, intraparticle diffusion equation, and the Elovich equation have been used to test experimental data. The experimental data was found to fit the second-order model and a chemisorptions mechanism. 0.7 M NaOH can be used for regeneration of spent SDH activated carbon with the efficiency of 99.6% and the regenerated carbon can be reused for five cycles effectively.     

Degradation of Benzo[a]Pyrene as Sole Carbon Source by a Non White Rot Fungus,Fusarium Solani

Non white rot fungi isolated from fuel-contaminated soil were screened for their ability to grow with benzo[a]pyrene as sole carbon source. The capacity of one isolate identified as F. solani F33 was further investigated by studying the mineralization of [7,10-¹⁴C]benzo[a]pyrene. Spores of F. solani were able to germinate in presence of benzo[a]pyrene and growing mycelium mineralized [7,10-¹⁴C]benzo[a]pyrene (0.2% over a period of 10 days). The amount of ¹⁴CO₂ released decreased of 66% in 10 days culture in the presence of the inhibitor of cytochrome P-450 1-aminobenzotriazole, suggesting that such enzymes are involved in benzo[a]pyrene degradation by F. solani. This hypothesis was also enhanced by observing, in F. solani grown on benzo[a]pyrene, the presence of small vesicles with high     

Statistical Optimization of Culture Conditions and Characterization for Ligninolytic Enzymes Produced from Rhizopus Sp. Using Prickly Palm Cactus Husk

Dry prickly palm cactus (Nopalea cochenillifera) husk was investigated as a substrate for Rhizopus sp. cultivation in the solid state, aiming at the production of laccase (Lac), lignin peroxidase (LiP), and manganese peroxidase (MnP). The optimization of fermentation was evaluated by an experimental design and it was obtained, for each enzyme, maximum productivities (U g^?1 h^?1) of: 0.085 ± 0.02 (MnP), 0.066 ± 0.001 (LiP), and 0.023 ± 2.3.10^?4 (Lac), at the conditions of 10 g of substrate, 72 h of fermentation, a_w = 0.865, and 30°C. The enzymes thermal and pH stabilities were evaluated and it was observed better results at temperatures no higher than 60°C and pH of 5.0; in addition, the storage of these enzymes was better at ? 25°C than at 4°C. Since the prickly palm cactus is an agricultural substrate and specially because of its low cost, it is important to propose different applications for it as, for example, an alternative substrate for biotechnological processes.     

Quantification of Bacillus subtilis and Bacillus sp. Adhesion on Fez Medina Cedar Wood

The adhesion of Bacillus subtilis and Bacillus sp. isolated from Fez cedar wood decay has been investigated. Furthermore, the physicochemical proprieties including hydrophobicity and electron donor/electron acceptor (Lewis acid–base) of both bacteria and substrata were evaluated using contact angle measurements. The results show that Bacillus subtilis has a hydrophobic character (ΔG _iwi = –20 mJ/m²). In contrast, Bacillus sp. exhibits a hydrophilic (ΔG _iwi = –20 mJ/m²), electron donating (γ^–) and weakly electron accepting (γ⁺) character. With respect to the substrata surface, we found that the cedar wood used in this work, was hydrophobic in character, having relatively more electron-donor that electron-acceptor properties (γ^– = 6 ± 4 mJ/m²; γ⁺ = 0 ± 3 mJ/m²). The phenomena of adhesion were observed by environmental scanning electron microscopy (ESEM) and cell adhesion was quantified using a Matlab program. The analysis of images obtained by ESEM show that the both cells was able to adhere to the wood substrata and the quantitative adhesion results showed that the surface coverage by Bacillus sp. (90%) was higher than that by the Bacillus subtilis strain (40%).     

Growth and pigment production of Synechocystis sp. PCC 6803 under shear stress

Cyanobacteria, such as Synechocystis, have recently become attractive hosts for sustainable production of biofuels and bio-fixation of CO₂ due to their genetic tractability and relatively fast growth. Cultivation of cyanobacteria requires shear stress, which is generated by mixing and air bubbling. In the present work, the impact of shear stress caused by stirring and air bubbling on the growth and pigment production of Synechocystis sp. PCC 6803 is investigated. For this purpose, agitated and airlift bubble column photobioreactors were used. The results showed that the growth and yield production were improved by mixing the culture system. However, there is a limit to this improvement: In the case of air bubbling, increasing shear stress (by rising air bubbling flow rate) to more than 185 mPa did not show any significant growth enhancement, while increasing the shear stress from 40 to 185 mPa improved the yield production up to 85%. At the optimal stirring rate, the yield production in the stirred photobioreactors increased by about 60% as compared to that of unstirred culture. The measurements of chlorophyll_a and carotenoid showed a strong correlation between biomass production and total pigment content. The highest level of cellular pigment (pigment per cell) was detected at the early stages of culture growth when cells were preparing for the rapid exponential growth phase.     

Impact of Exogenous Silicate Amendments on Nitrogen Metabolism in Wheat Seedlings Subjected to Arsenate Stress

We intended to investigate the response of arsenate on nitrogen metabolism in wheat seedlings and aimed to assess the efficacy of silicon amendments in modulating the metabolic disturbances caused by arsenate stress. The nitrogen metabolism of wheat cultivated in different levels of arsenate with or without silicate in a medium supplemented with modified Hoagland’s solution for 21 days was studied. Experimental design was completely randomized with different arsenate concentrations (0, 25, 50 and 100 μM) with or without 5 mM silicate. Arsenate treatment decreased growth along with decline in nitrate (NO3−) uptake and accumulation. Activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) as well as glutamate synthase (GOGAT) were lowered in the test seedlings. Decline in nitrite (NO2−) and amino acid contents were also evident along with an enhancement in the accumulation of toxic ammonia. Silicate supplementation under arsenate stress however, improved growth, repaired the arsenate-induced effects leading to an enhancement in nitrate (NO3−) uptake and consequently improved nitrite (NO2−) and amino acid contents as well. The total and soluble nitrogen contents were enhanced along with enhancements in activities of enzymes associated with nitrate metabolism while ammonia accumulation was lowered. Results therefore, imply the involvement of exogenous silicon amendments in relieving the metabolic alterations in nitrogen metabolism caused by arsenate stress that enabled wheat seedlings to adapt under arsenate excess and eventually promoted plant growth.     

Combination of a crude oil-degrading bacterial consortium under the guidance of strain tolerance and a pilot-scale degradation test

Under the guidance of strain tolerance, a new combinationmethod for crude oil-degrading bacterial consortium was studied. Firstly,more than 50 efficient crude oil-degrading and biosurfactant producing bacteriawere isolated from petroleum-contaminated soil andwater in Tianjin Binhai New Area Oilfield, China. Twenty-four of them were selected for further study. These strains were identified as belonging Pseudomonas aeruginosa, Bacillus subtilis, Brevibacillus brevis, Achromobacter sp., Acinetobacter venetianus, Lysinibacillus macroides, Klebsiella oxytoca, Stenotrophomonas rhizophila, Rhodococcus sp. and Bacillus thuringiensis. A shake-flask degradation test revealed that 12 of these strains could degrade over 50% of 1% crude oil concentration in 7 d. Of these, 8 strains were able to produce biosurfactants. Furthermore, environmental tolerance experiments indicated that the majority of the strains had the ability to adapt to extreme environments including high temperatures, alkaline environments and high salinity environments. A mixed bacterial agent comprising the strains WB2, W2, W3 and HA was developed based on the environmental tolerance tests and subjected to the pilot-scale degradation test indicating that this bacterial agent could degrade 85.2% of 0.8% crude oil concentration in 60 d. Our results suggest that the application of this mixed agent could remediate crude oil polluted soils in saline and alkaline environments.     

搅拌槽反应器中中度嗜热浸矿菌预处理含砷金矿

从多个矿坑、煤堆废水中富集中度嗜热浸矿菌,并在搅拌反应器中经过两年的长期驯化,获得能耐受高矿浆浓度和具有抗砷性的浸矿混合菌. 对浸矿混合菌进行耐高矿浆浓度的驯化,保持矿浆浓度为200 g/L,改变两种金矿的配比,提高驯化体系中砷含量,进行耐砷性驯化. 用驯化的浸矿混合菌对难处理金矿进行生物氧化预处理,矿浆浓度为200 g/L,砷含量为8 g/L,14 d时菌体浓度最大,达2′109 mL-1,22 d时砷浸出率为59.93%. 采用限制性酶切片段长度多态性分析对浸矿14和22 d时的微生物多样性进行分析,发现存在Sulfobacillus sp., Acidithiobacillus caldus, Ferroplasma thermophilum和Pseudomonas sp..     

Decolorization of Brilliant Blue G dye mediated by degradation of the microbial consortium of Galactomyces geotrichum and Bacillus sp.

A consortium-GB containing two microorganisms Galactomyces geotrichum MTCC 1360 and Bacillus sp. VUS was able to degrade sulfur-containing dye Brilliant Blue G, optimally at pH 9 and temperature at 50 °C. The ability of consortium-GB to work at higher temperature and pH ranges will help in using this consortium for removal of the dye from textile effluent. Malt extract, peptone and beef extract were found to be the best additional carbon and nitrogen sources. Brilliant Blue G caused enhancement of the riboflavin reductase among the enzyme activities studied. Biodegradation was confirmed by analyzing the product using UV–vis, HPLC, and FTIR. The GC–MS study revealed a pathway of Brilliant Blue G with release of (4-ethoxy-phenyl)-phenyl-amine and 3-ethylaminomethyl-benzenesulfonic acid as final metabolites formed by the consortium-GB. GC–MS analysis indicated the formation of 3-{[ethyl-(3-methyl-cyclohexa-2,5-dienyl)-amino]-methyl}-benzenesulfonic acid as a product by G. geotrichum MTCC 1360 alone and (4-benzylidene-3-methyl-cyclohexa-2,5-dienylidene)-methyl-amine by Bacillus sp. VUS alone. Phytotoxicity revealed nontoxic nature of the metabolites. These results indicate the high potential of the consortium-GB to serve as an excellent biomass for the use in Brilliant Blue G dye removal.     

FED-BATCH FERMENTATION OF BACILLUS CLAUSII FOR EFFICIENT PRODUCTION OF ALKALINE PROTEASE USING DIFFERENT FEEDING STRATEGIES

The effect of different feeding strategies, involving constant rate and linear feeding with negative and positive slopes, on protease production of an indigenous Bacillus clausii was investigated. The results indicated that alkaline protease was produced at high levels soon after glucose was completely consumed. Alkaline protease activity was at a maximum during the constant feeding rate and in the absence of glucose and presence of mineral salts and yeast extract in the feed medium. Maximum protease production in the fed-batch culture using an optimized level of feeding composition was 2430 ± 67 U/mL, which increased by up to 35% when compared to the 1800 ± 14 U/mL produced during batch culture. During batch fermentation, the protease yield and productivity obtained were 90000 U/g and 64285 U/L · h; however, under fed-batch conditions, these were 121500 U/g and 71470 /L · h, respectively. Hence, the suggested strategy has the potential to be applied to industrial production of protease used in detergent products.     

Effect of aeration and pH on gramicidin S production by Bacillus brevis

Although the biosynthesis of the antibiotic gramicidin S (GS) by Bacillus brevis ATCC 9999 has been studied extensively, almost no attention has been given to environmental control of its fermentation process. In this respect, GS fermentations conducted in a 7.5 dm³ fermentor in complex (YP) medium revealed that a high aeration rate resulted in a high biomass yield (12 g DCW dm^?3) with very low GS levels (170 mg GS dm^?3). Lowering the aeration rate (5 dm³ air min^?1 at 300 rev min^?1) caused a dramatic increase in GS formation (2100 mg GS dm^?3) and comparable but slower biomass formation. In chemically-defined (F3/6) medium fermentations, an aeration rate of 5 dm³ air min^?1 at 300 rev min^?1 was apparently too high as only 0.104 mg GS mg^?1 DCW was produced. A much lower aeration rate (2 dm³ air min^?1 at 250 rev min^?1) was needed to arrive at a higher specific antibiotic level: 0.130 mg GS mg^?1 DCW. These data seem compatible with the finding that oxygen is known to inactivate the GS-synthetases. Furthermore, keeping the pH constant at 7.3 under low aeration conditions increased specific GS production up to 0.220 mg GS mg^?1 DCW in YP, as well as in F3/6 fermentations. Both environmental pH and dissolved oxygen tension clearly affect growth pattern, growth extent and GS production in these high yielding media. These data stress the importance of controlling pH and aeration rate during GS fermentations.