Biodegradation of nitrobenzene by a sequential anaerobic-aerobic process

Nitrobenzene was completely degraded by mixed cultures using a sequential anaerobic-aerobic treatment process. Under anaerobic conditions in a fixed-bed column aniline was formed from nitrobenzene through gratuitous reduction by cells of sewage sludge. This reaction was accelerated by the addition of glucose. Complete mineralization of aniline was accomplished by subsequent aerobic treatment using activated sludge as inoculum. The maximum degradation rate of nitrobenzene (4.5 mM) in the two-stage system was 552 mg l^–1d^–1, referring to 154 mg of nitrobenzene per gram of glucose. In a second experimental phase glucose as cosubstrate and H-donor was replaced by synthetic waste containing ethanol, methanol, isopropanol and acetone. Again, nitrobenzene (1.9 mM) was completely degraded (maximum degradation rate of 237 mg l^–d^–1, referring to 251 mg per gram of solvents). The major advantage of the described two-stage process is that the reduction of nitrobenzene by anaerobic pretreatment drastically reduces emission by stripping during aerobic treatment.Abbreviations HRT hydraulic retention time - OD₅₄₆ optical density at 546 nm     

Anaerobic degradation of phenol in batch and continuous cultures by a denitrifying bacterial consortium

Summary The anaerobic degradation of phenol under denitrifying conditions by a bacterial consortium was studied both in batch and continuous cultures. Anaerobic degradation was dependent on NO_f3 ^p– and concentrations up to 4 mm phenol were degraded within 2–5 days. During continuous growth in a fermenter, steady states could be maintained at eight dilution rates (D) corresponding to residence times between 12.5 and 50 h. Culture wash-out occurred at D=0.084 h^–1. The kinetic parameters obtained for anaerobic degradation of phenol under denitrifying conditions by the consortium were: maximam specific growth rate = 0.091 h^–1; saturation constant = 4.91 mg phenol/l; true growth yield = 0.57 mg dry wt/mg phenol; maintenance coefficient = 0.013 mg phenol/mg dry wt per hour. The Haldane model inhibition constant was estimated from batch culture data giving a value of 101 mg/l. The requirement of CO₂ for the anaerobic degradation of phenol with NO_f3 ^p– indicates that phenol carboxylation to 4-hydroxybenzoate was the first step of phenol degradation by this culture. 4-Hydroxybenzoate, proposed as an intermediate of phenol carboxylation under these conditions, was detected only in continuous cultures at very low growth rates (D=0.02 h^–1), but was never detected as a free intermediary metabolite either in batch or in continuous cultures. Correspondence to: N. Khoury     

High yield mixotrophic cultures of the marine microalga Tetraselmis suecica (Kylin) Butcher (Prasinophyceae)

The effects of three organic compounds were tested on one of the most used marine micro-algae in the aquaculture of molluscs and crustaceans, Tetraselmis suecica. Studies were made in axenic conditions with yeast extract, peptone and glucose added to the culture medium, each alone, in combinations of two or all together. Medium without any organic compound was used for the control. Cultures containing yeast extract grew best, reaching maximum cell density of 3.79 × 10⁶ and 3.84 × 10⁶ cells ml⁻¹. The organic carbon source affected the biochemical composition. The components most affected were the carbohydrates, with values between 6.5 pg cell⁻¹ in control cultures and 48.5 pg cell⁻¹ in glucose cultures. Protein content ranged between 27.5 pg cell⁻¹ in control cultures and 88.6 pg cell⁻¹ in yeast + glucose + peptone cultures. The lipid content changed little. Maximum protein yields were reached in cultures with yeast + glucose and with yeast - glucose - peptone, with values of 24.6 and 28.2 mg 1⁻¹ d⁻¹, respectively. These values are 22 and 25 times those in control cultures. A maximum carbohydrate yield of 7.9 mg carbohydrate per litre per day was obtained in yeast + glucose + peptone cultures, 27 times that in the control cultures. The maximum lipid yield was obtained with yeast + glucose + peptone and yeast + glucose. Maximum energy values were 308 kcal 1⁻ in yeast extract - glucose - peptone cultures and 279 kcal 1⁻¹ in yeast extract + glucose cultures. Gross energy values in control cultures were 24.5 kcal 1⁻¹, but peptone cultures presented the minimum energy value, 22 kcal 1⁻¹. The yeast extract: glucose ratio in the culture medium was optimized. A ratio 2:1 produced the best yields in cells, protein, carbohydrate and gross energy.     

METABOLISM OF TISSUE CULTURES : III. A METHOD FOR MEASURING THE PERMEABILITY OF TISSUE CELLS TO SOLUTES

By using radioactive isotopes in tissue cultures, the rate of permeation of substances into cells can be measured independently of concurrent metabolic reactions of these substances. Techniques of obtaining and analyzing data are described. Examples are given using radioactive potassium and phosphorus. Using cultures of chick embryo muscle, turnover time for cell potassium is 6 hours, and for cell inorganic phosphate is 7 hours in the examples cited. Permeability rates, based on estimates of the cell surface involved and expressed as millimoles per cm.² per hour, are of the order of magnitude of 10^–6 for potassium and of 10^–7 for phosphate.     

Fundamental Mechanisms of Phosphate Removal by Anaerobic/Aerobic Activated Sludge in Treating Municipal Wastewater

Acetate is thought to be an important substrate for phosphate removal in anaerobic/aerobic activated sludge (AS) processes. The acetate content in municipal wastewater is low, and the main organic compounds in such wastewater are particulate organic matters (POMs) that are converted to endogenous substrates in AS processes when municipal wastewater is introduced into AS reactors. The question which then arises is which substrate, acetate or POM, is important for phosphate removal in full‐scale AS plants. The rates of phosphate release and substrate uptake were determined using AS harvested from a full‐scale anaerobic/aerobic AS plant and also AS acclimated to peptone under alternate anaerobic and aerobic conditions for 26 months. The rate of phosphate release upon POM addition per AS concentration per unit of time was about 0.84 mg PO₄‐P/(g MLSS·h) irrespective of the wastewater quality. This value was about 0.05 in the case of AS acclimated to peptone for 26 months. When the AS concentration is 2.5 g/L and the mixed liquor retention time is 2 h in the anaerobic zone, about 4.2 mg/L PO₄‐P is released upon POM addition. Hence, phosphate can be removed from municipal wastewater using full‐scale AS plants running under these conditions.     

Effect of ammonia on the anaerobic degradation of protein by a mesophilic and thermophilic biowaste population

The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was investigated. For peptone concentrations from 5 g l⁻¹ to 20 g l⁻¹ the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l⁻¹ day⁻¹ compared to 320 mg l⁻¹ day⁻¹ at 10 g l⁻¹ peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH₃/g peptone in the mesophilic cultures. If 0.5–6.5 g l⁻¹ ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand (COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures were most active if around 1 g ammonia l⁻¹ was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and methane formation revealed a K _i (50%) for NH₃ of 92, 95 and 88 mg l⁻¹ at 37 °C and 251, 274 and 297 mg l⁻¹ at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH₃ than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 10⁸ peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only 5.6 × 10⁷ cfu/ml was observed. Received: 24 April 1998 / Received revision: 26 June 1998 / Accepted: 27 June 1998     

Hydrogen formation by cyanobacteria cultures selected for nitrogen fixation

Seventy-one cyanobacteria containing cultures were enriched from various soil and water locations either under aerobic and/or anaerobic conditions on agar medium selective for nitrogen fixation. Kept under argon containing 1% CO₂ for 24 and 48 h most of these cultures evolved hydrogen at very variable rates up to 116 l per mg chlorophyll and hour as a mean value over a time period of 24h. Several samples evolved hydrogen more efficiently compared with known hydrogen producing pure strains from culture collections. Thirty-one of the investigated cultures showed a hydrogen formation higher than 10 l per mg chlorophyll and hour measured over 24 or 48 h. Among these all the morphological forms of cyanobacteria i.e. unicellular and filamentous with or without heterocysts are found. Hence, selecting for nitrogen fixing cyanobacteria seems to be a practical method to find efficient hydrogen producers.     

Characterization of precipitates formed by H2S-producing, Cu-resistant Firmicute isolates of Tissierella from human gut and Desulfosporosinus from mine waste

The purpose of this study was to characterize precipitates formed in anaerobic, H₂S-producing cultures of two Tissierella isolates and Desulfosporosinus strain DB. The cultures were grown in Cu-containing media as part of a larger study of Cu resistance in anaerobic sulfidogens. The Tissierella strains produced H₂S from peptone. Desulfosporosinus formed H₂S from peptone or through dissimilatory sulfate reduction with lactate. Tissierella cultures precipitated iron phosphate, vivianite, but no crystalline phases or Cu sulfides were detected. Multiple Cu sulfides, including chalcopyrite and covellite, were detected in Desulfosporosinus cultures but vivianite was not formed. Ion microprobe spectra and electron microscopic examination showed major variation in the elemental composition and morphological differences depending on incubation conditions. Extended incubation time for at least 1–2 months increased the crystallinity of the precipitates. The results highlight biogeochemical differences in sulfide and phosphate precipitates between the two major groups of Firmicutes although they may share the same habitat including the human intestinal tract.     

Stoichiometry and kinetics of microbial toluene degradation under denitrifying conditions

Batch experiments were carried out to investigate the stoichiometry and kinetics of microbial degradation of toluene under denitrifying conditions. The inoculum originated from a mixture of sludges from sewage treatment plants with alternating nitrification and denitrification. The culture was able to degrade toluene under anaerobic conditions in the presence of nitrate, nitrite, nitric oxide, or nitrous oxide. No degradation occurred in the absence of Noxides. The culture was also able to use oxygen, but ferric iron could not be used as an electron acceptor. In experiments with¹⁴C-labeled toluene, 34%±8% of the carbon was incorporated into the biomass, while 53%±10% was recovered as¹⁴CO₂, and 6%±2% remained in the medium as nonvolatile water soluble products. The average consumption of nitrate in experiments, where all the reduced nitrate was recovered as nitrite, was 1.3±0.2 mg of nitrate-N per mg of toluene. This nitrate reduction accounted for 70% of the electrons donated during the oxidation of toluene. When nitrate was reduced to nitrogen gas, the consumption was 0.7±0.2 mg per mg of toluene, accounting for 97% of the donated electrons. Since the ammonia concentration decreased during degradation, dissimilatory reduction of nitrate to ammonia was not the reductive process. The degradation of toluene was modelled by classical Monod kinetics. The maximum specific rate of degradation, k, was estimated to be 0.71 mg toluene per mg of protein per hour, and the Monod saturation constant, K _s , to be 0.2 mg toluene/l. The maximum specific growth rate, _max , was estimated to be 0.1 per hour, and the yield coefficient, Y, was 0.14 mg protein per mg toluene.Abbreviations NVWP Non Volatile Water-soluble Products     

Activity of root systems of six plant species at different stages of development

Summary A number of data on root performance of six different crop species during development were measured. The plants wre cultivated in nutrient solution. Normal plant requirements were in the range of 4 mg O₂ per g dry root per hour, 0.2–4μg K per cm² total root surface per hour,² 0.2–2μg NO₃ per om² total root surface per hour. An attempt was made to establish a ratio between forced water entry and total root surface as a measure of functional root surface. The indication is that the relative surface of permeable root remains dominant during the phase of exponential growth and declines thereafter. The data collected are considered to be representative of normal requirements. They compare well with results published in the literature.     

INVERSE ENZYMATIC CHANGES IN NEURONS AND GLIA DURING INCREASED FUNCTION AND HYPOXIA

Following stimulation of the vestibular nerve in the rabbit, respiratory enzyme activities increased in Deiters' nerve cells. The anaerobic glycolysis, measured as 10^-4 µl CO₂ per hour per cell, was found to decrease concomitantly by 25 to 40 per cent, suggesting a Pasteur effect. By contrast, in the surrounding glia the anaerobic glycolysis increased and the respiratory enzyme activity decreased, suggesting a Crabtree effect. The evidence is discussed for a regulatory metabolic mechanism operating between the neuron and its glia. Hypoxia of 8 per cent O₂ caused an increase of both oxygen consumption and CO₂ production in the nerve cells, but did not change the glia values.     

Methane emissions from fen,bog and swamp peatlands in Quebec

A static chamber technique was used weekly from spring thaw to winter freezing to measure methane emissions from 10 sites representing subarctic fens and temperate swamps and bogs. Rates of < 200 mg CH₄ m^–2 d^–1 were recorded in subarctic fens: within-site emissions were primarily controlled by the evolution of the peat thermal regime, though significant releases during spring thaw were recorded at some sites. Between subarctic fens, topography and water table elevation were important controls on methane emissions, with the general sequence: pool = horizontal fen> string. Emission rates from the 2 swamp sites were lower (< 20 mg CH₄ m^–2 d^–1 ), except during the spring thaw and when the sites were saturated. The low water table ( < 80 cm depth) in abnormally dry years reduced emission rates; rates were also low from a swamp site which had been drained and cleared of vegetation for horticulture. Methane emission rates were also low (< 5 mg CH₄ m^–2 d^–1) from 2 ombrotrophic bog sites. Laboratory measurements of rates of methane production under anaerobic conditions and methane consumption under aerobic conditions revealed that production rates were generally highest in the surface layers (0 to 2.5 cm depth); production was high in the fens and very low in the bogs. The swamp samples were able to produce methane under anaerobic conditions, but were also able to consume methane under aerobic conditions. Annual methane emission rates are estimated to be 1 to 10 g CH₄ m^–2 from the fens, 1 to 4 g CH4 m^–2 from the swamps and <0.2 g CH₄ m^–2 from the bogs and drained swamp.     

Evolutionary engineering of a glycerol‐3‐phosphate dehydrogenase‐negative,acetate‐reducing Saccharomyces cerevisiae strain enables anaerobic growth at high glucose concentrations

Glycerol production by Saccharomyces cerevisiae, which is required for redox-cofactor balancing in anaerobic cultures, causes yield reduction in industrial bioethanol production. Recently, glycerol formation in anaerobic S. cerevisiae cultures was eliminated by expressing Escherichia coli (acetylating) acetaldehyde dehydrogenase (encoded by mhpF) and simultaneously deleting the GPD1 and GPD2 genes encoding glycerol-3-phosphate dehydrogenase, thus coupling NADH reoxidation to reduction of acetate to ethanol. Gpd^– strains are, however, sensitive to high sugar concentrations, which complicates industrial implementation of this metabolic engineering concept. In this study, laboratory evolution was used to improve osmotolerance of a Gpd^– mhpF-expressing S. cerevisiae strain. Serial batch cultivation at increasing osmotic pressure enabled isolation of an evolved strain that grew anaerobically at 1 M glucose, at a specific growth rate of 0.12 h⁻¹. The evolved strain produced glycerol at low concentrations (0.64 ± 0.33 g l⁻¹). However, these glycerol concentrations were below 10% of those observed with a Gpd⁺ reference strain. Consequently, the ethanol yield on sugar increased from 79% of the theoretical maximum in the reference strain to 92% for the evolved strains. Genetic analysis indicated that osmotolerance under aerobic conditions required a single dominant chromosomal mutation, and one further mutation in the plasmid-borne mhpF gene for anaerobic growth.     

Growth and Nitrogen Uptake Kinetics in Cultured Prorocentrum donghaiense

We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO₃ ⁻), ammonium (NH₄ ⁺), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L⁻¹ for NO₃ ⁻ and NH₄ ⁺, 0.5–50 μmol N L⁻¹ for urea, 0.5–100 μmol N L⁻¹ for glu and cyanate, and 0.5–200 μmol N L⁻¹ for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μ_m, 1.51±0.06 d⁻¹ and 1.50±0.05 d⁻¹, respectively). However, cultures grown on cyanate, NO₃ ⁻, and NH₄ ⁺ had lower half saturation constants (K_μ, 0.28–0.51 μmol N L⁻¹). N uptake kinetics were measured in NO₃ ⁻-deplete and -replete batch cultures of P. donghaiense. In NO₃ ⁻-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO₃ ⁻, NH₄ ⁺, urea and algal amino acids; uptake was saturated at or below 50 μmol N L⁻¹. In NO₃ ⁻-replete batch cultures, NH₄ ⁺, urea, and algal amino acid uptake kinetics were similar to those measured in NO₃ ⁻-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth.     

Hydrogenase-3 Contributes to Anaerobic Acid Resistance of Escherichia coli

Background

Hydrogen production by fermenting bacteria such as Escherichia coli offers a potential source of hydrogen biofuel. Because H₂ production involves consumption of 2H⁺, hydrogenase expression is likely to involve pH response and regulation. Hydrogenase consumption of protons in E. coli has been implicated in acid resistance, the ability to survive exposure to acid levels (pH 2–2.5) that are three pH units lower than the pH limit of growth (pH 5–6). Enhanced survival in acid enables a larger infective inoculum to pass through the stomach and colonize the intestine. Most acid resistance mechanisms have been defined using aerobic cultures, but the use of anaerobic cultures will reveal novel acid resistance mechanisms.

Methods and Principal Findings

We analyzed the pH regulation of bacterial hydrogenases in live cultures of E. coli K-12 W3110. During anaerobic growth in the range of pH 5 to 6.5, E. coli expresses three hydrogenase isoenzymes that reversibly oxidize H₂ to 2H⁺. Anoxic conditions were used to determine which of the hydrogenase complexes contribute to acid resistance, measured as the survival of cultures grown at pH 5.5 without aeration and exposed for 2 hours at pH 2 or at pH 2.5. Survival of all strains in extreme acid was significantly lower in low oxygen than for aerated cultures. Deletion of hyc (Hyd-3) decreased anoxic acid survival 3-fold at pH 2.5, and 20-fold at pH 2, but had no effect on acid survival with aeration. Deletion of hyb (Hyd-2) did not significantly affect acid survival. The pH-dependence of H₂ production and consumption was tested using a H₂-specific Clark-type electrode. Hyd-3-dependent H₂ production was increased 70-fold from pH 6.5 to 5.5, whereas Hyd-2-dependent H₂ consumption was maximal at alkaline pH. H₂ production, was unaffected by a shift in external or internal pH. H₂ production was associated with hycE expression levels as a function of external pH.

Conclusions

Anaerobic growing cultures of E. coli generate H₂ via Hyd-3 at low external pH, and consume H₂ via Hyd-2 at high external pH. Hyd-3 proton conversion to H₂ is required for acid resistance in anaerobic cultures of E. coli.     

Detection of 2,4,6-Trinitrotoluene-Utilizing Anaerobic Bacteria by 15N and 13C Incorporation

2,4,6-Trinitrotoluene (¹⁵N or ¹³C labeled) was added to Norfolk Harbor sediments to test whether anaerobic bacteria use TNT for growth. Stable-isotope probing (SIP)-terminal restriction fragment length polymorphism (TRFLP) detected peaks in the [¹⁵N]TNT cultures (60, 163, and 168 bp). The 60-bp peak was also present in the [¹³C]TNT cultures and was related to Lysobacter taiwanensis.It has been estimated that there are over 1 million cubic yards of material contaminated with 2,4,6-trinitrotoluene (TNT) in the United States at concentrations as high as 600,000 to 700,00 mg/kg of material (9). Marine and estuarine sediments have also been impacted through the manufacturing, use, and/or disposal of TNT. Microbial biodegradation of these pollutants in situ is preferable due to the large volume of contaminated soils/sediments. However, it is unclear whether in situ bacteria can utilize TNT as a nitrogen or carbon source. Under aerobic conditions, TNT appears to be largely unavailable to bacteria but can be used by a variety of fungi as a carbon and nitrogen source (7). Under anaerobic conditions, only a few bacterial strains (Clostridium and Desulfovibrio strains and Pseudomonas sp. strain JLR11) have been reported to utilize TNT as a sole nitrogen source (6, 7). It is widely believed that nitroaromatic compounds cannot serve as growth substrates under anaerobic conditions in situ (11), and coamendment strategies are suggested for stimulating TNT transformation to 2,4,6-triaminotoluene (TAT) (1, 7, 18). Given these difficulties, there is no direct evidence that TNT can be biodegraded in situ and there is little proof that anaerobic bacteria can utilize TNT as a sole carbon or nitrogen source in organic-rich sediments. This study tested whether bacteria in Norfolk Harbor sediment are able to incorporate nitrogen (N) or carbon (C) from TNT into biomass under sulfidogenic conditions using stable-isotope probing (SIP). The findings indicate that bacteria assimilate ¹⁵N and ¹³C from TNT into their genomes during anaerobic incubations (2 to 35 days). Interestingly, one small-subunit (SSU) gene, related to Lysobacter taiwanensis, was observed in both the ¹⁵N and the ¹³C incubations.     

ON THE RATE OF OXYGEN CONSUMPTION BY FERTILIZED AND UNFERTILIZED EGGS : IV. CHAETOPTERHS AND ARBACIA PUNCTULATA

1. Unfertilized eggs of Chaetopterus consume about 2.4 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C. 2. In the 1st hour after fertilization, the fertilized eggs consume oxygen at about 53 or 54 per cent of this rate, which is about 1.3 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C. 3. For the first 6 hours after fertilization, at 21°C., the curve of the rate of oxygen consumption is slightly asymmetrically sigmoid. The prefertilization rate is regained between 4½ and 5 hours after fertilization. Soon after 6 hours, ciliary activity begins, and the rate of oxygen consumption rises rapidly. 4. The unfertilized eggs of Arbacia punctulata consume about 0.36–0.5 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C. The absolute determination is difficult as these eggs are highly sensitive to shaking in the manometer vessels, and these difficulties are discussed. 5. The fertilized eggs of Arbacia punctulata consume oxygen at the rate of about 2.0 mm.³ O₂ per hour per 10 mm.³ 21°C. At 1 hour after fertilization the rate is already rising. 6. A comparison of the absolute rates of oxygen consumption, and the changes in rate at fertilization of these and a number of other eggs, together with a theoretical discussion, and a discussion of discrepancies in measurements on the eggs of Arbacia punctulata, is contained in the fifth paper of this series (21).     

Lipid formation by Cryptococcus albidus in nitrogen-limited and in carbon-limited chemostat cultures

Summary Cryptococcus albidus var. Albidus CBS 4517 was grown in nitrogen-limited and in carbon-limited chemostat cultures. The effect of growth rate and limiting nutrient on lipid accumulation and fatty acid composition was investigated.The maximum lipid content in the biomass was, in both cultivation systems, observed at the lowest dilution rate (growth rate) tested. At this dilution rate, D=0.31 h^-1, cells from the nitrogen-limited culture contained 41% (w/w) lipid and cells from the carbon-limited culture 37%. These results indicate the ability of C. albidus, unlike other oleaginous yeasts, to accumulate lipid also in carbon-limited chemostats.The yield of lipid from carbon source was about the same at D=0.031 h^-1 in nitrogen-limited (Y _L/S=0.16 g/g) as in carbon-limited (Y _L/S=0.17 g/g) cultures and decreased with increasing growth rates. In the nitrogen-limited culture, the lipid productivity was about constant at low growth rates (0.031–0.056 h^-1) and a slight decrease was observed at D=0.08 h^-1, while the specific lipid productivity, q _L, increased to 27.5 mg/g per hour. In the carbon-limited culture, however, lipid productivity increased with increasing growth rates and reached its maximum value near _max, whereas q _L was about constant at 20 mg/g per hour.The fatty acid composition was influenced by the specific growth rate in nitrogen-limited as well as in carbon-limited cultures, although the changes were more pronounced during carbonlimitation. A decrease in the degree of unsaturation (/mole) was also observed with increasing lipid content in the cells.     

THE OXYGEN CONSUMPTION OF LUMINOUS BACTERIA

Oxygen consumption of luminous bacteria determined by the Thunberg micro respirometer and by the time which elapses before the luminescence of an emulsion of luminous bacteria in sea water begins to dim, when over 99 per cent of the dissolved oxygen has been consumed, agree exactly. Average values for oxygen consumption at an average temperature of 21.5°C. are 4.26 x 10^–11 mg. O₂ per bacterium; 2.5 x 10⁴ mg. per kilo and 5.6 mg. O₂ per sq. m. of bacterial surface. The only correct comparison of the oxygen consumption of different organisms or tissues is in terms of oxygen used per unit weight with a sufficient oxygen tension so that oxygen consumption is independent of oxygen tension. Measurement of the oxygen concentration which just allows full luminescence, compared with a calculation of the oxygen concentration at the surface of a bacterial cell just necessary to allow the observed respiration throughout all parts of the cell, indicates that oxygen must diffuse into the bacterium much more slowly than through gelatin or connective tissue but not as slowly as through chitin.     

Effect of oxygen on denitrification in continuous chemostat culture withComamonas sp SGLY2

Continuous cultures ofComamonas sp SGLY2 were grown anaerobically prior to establishing steady states at different oxygen flow rates. At a low oxygen transfer rate, no dissolved oxygen accumulated in the medium and all nitrate was reduced to dinitrogen. Concurrently with the increase of dissolved oxygen concentration in the liquid phase, the rate of denitrification decreased. However, at a dissolved oxygen concentration near saturation (33 mg L^–1), a part of the electron flow always diverted to nitrate with production of dinitrogen: the aerobic denitrification rate was equivalent to 35% of that calculated under anaerobic conditions. These experiments reflected the co-utilization of oxygen and N-oxides and the production of dinitrogen, up to saturated conditions, which implied synthesis and activity of the four denitrifying enzymes under various aeration conditions.