Transformation of 1,1,1-trichloroethane in an anaerobic packed-bed reactor at various concentrations of 1,1,1-trichloroethane, acetate and sulfate

Biotransformation of 1,1,1-trichloroethane (CH₃CCl₃) was observed in an anaerobic packed-bed reactor under conditions of both sulfate reduction and methanogenesis. Acetate (1 mM) served as an electron donor. CH₃CCl₃ was completely converted up to the highest investigated concentration of 10 μM. 1,1-Dichloroethane and chloroethane were found to be the main transformation products. A fraction of the CH₃CCl₃ was completely dechlorinated via an unknown pathway. The rate of transformation and the transformation products formed depended on the concentrations of CH₃CCl₃, acetate and sulfate. With an increase in sulfate and CH₃CCl₃ concentrations and a decrease in acetate concentration, the degree of CH₃CCl₃ dechlorination decreased. Both packed-bed reactor studies and batch experiments with bromoethanesulfonic acid, an inhibitor of methanogenesis, demonstrated the involvement of methanogens in CH₃CCl₃ transformation. Batch experiments with molybdate showed that sulfate-reducing bacteria in the packed-bed reactor were also able to transform CH₃CCl₃. However, packed-bed reactor experiments indicated that sulfate reducers only had a minor contribution to the overall transformation in the packed-bed reactor. Received: 22 January 1997 / Received revision: 12 May 1997 / Accepted: 19 May 1997     

Choline and acetylcholine: novel cationic osmolytes in Lactobacillus plantarum

The aim of this work was to study the physiological response of Lactobacillus plantarum subjected to osmotic stress in the presence of three structurally related compatible solutes. Either betaine, choline or acetylcholine was accumulated by osmotically stressed cells when provided in the chemically defined medium. Choline and acetylcholine were accumulated to maximum concentrations of 139 and 222 μmol g (dry weight) of cells⁻¹ respectively and were not converted to betaine. Addition of 0.5 mM choline or 0.5 mM acetylcholine to the medium increased the growth rates of cells in media with various amounts of added sodium chloride. Both choline and acetylcholine are positively charged compounds; therefore, it was presumed that charged intracellular solutes could counterbalance the excess of positive charge. Intracellular inorganic ion levels (K⁺, SO²⁻ ₄, PO³⁻ ₄ and Cl⁻) of cells cultured under conditions of osmotic stress remained similar in the presence of either betaine, choline or acetylcholine. However, cells cultured in the presence of choline or acetylcholine accumulated an additional quantity of approximately 125 or 200 μmol.glutamate (dry weight) cells⁻¹ respectively, as compared to cells grown in the presence of betaine. Hence glutamate appears to be the counterion for choline and acetylcholine. This is the first study demonstrating accumulation of choline and acetylcholine in lactic acid bacteria subjected to osmotic stress. Received: 5 February 1997 / Received revision: 15 April 1997 / Accepted: 19 April 1997     

Anaerobic biodegradability of alkylphenols and fuel oxygenates in the presence of alternative electron acceptors

Alkylphenols and fuel oxygenates are important environmental pollutants produced by the petrochemical industry. A batch biodegradability test was conducted with selected ortho-substituted alkylphenols (2-cresol, 2,6-dimethylphenol and 2-ethylphenol), fuel oxygenates (methyl tert-butyl ether, ethyl tert-butyl ether and tert-amylmethyl ether) and tert-butyl alcohol (TBA) as model compounds. The ortho-substituted alkylphenols were not biodegraded after 100 days of incubation under methanogenic, sulfate-, or nitrate-reducing conditions. However, biodegradation of 2-cresol and 2-ethylphenol (150 mg l⁻¹) was observed in the presence of Mn (IV) as electron acceptor. The biodegradation of these two compounds took place in less than 15 days and more than 90% removal was observed for both compounds. Mineralization was indicated since no UV-absorbing metabolites accumulated after 23 days of incubation. These alkylphenols were also slowly chemically oxidized by Mn (IV). No biodegradation of fuel oxygenates or TBA (1 g l⁻¹) was observed after 80 or more days of incubation under methanogenic, Fe (III)-, or Mn (IV)-reducing conditions, suggesting that these compounds are recalcitrant under anaerobic conditions. The fuel oxygenates caused no toxicity towards acetoclastic methanogens activity in anaerobic granular sludge. Received: 8 February 2000 / Received revision: 15 May 2000 / Accepted: 19 May 2000     

Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus

The influence of (NH₄)₂SO₄ concentration and dilution rate (D) on actual and potential H₂ photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H₂ production in a photobioreactor was maximal (approx. 80 ml h⁻¹l⁻¹) at D = 0.06 h⁻¹ and 4 mM (NH₄)₂SO₄. However, it was lower than the potential H₂ evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h⁻¹ l⁻¹ at D = 0.03–0.08 h⁻¹. Taking into account the fact that H₂ production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting) factor should be sought. One possibility is an inhibition of H₂ production by the H₂ accumulated in the gas phase. This is apparent from the non-linear kinetics of H₂ evolution in the vials or from its inhibition by the addition of H₂; initial rates were restored in both cases after the vials had been refilled with argon. The actual H₂ production in the photobioreactor at D = 0.06 h⁻¹ was shown to increase from approximately 80 ml h⁻¹ l⁻¹ to approximately 100 ml h⁻¹ l⁻¹ under an argon flow at 100 ml min⁻¹. Under maximal H₂ production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H₂ production and 50% for biomass synthesis. Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997     

Treatment of cyanide-containing wastewater from the food industry in a laboratory-scale fixed-bed methanogenic reactor

During the process of producing cassava starch from Manihot esculenta roots, large amounts of cyanoglycosides were released, which rapidly decayed to CN⁻ following enzymatic hydrolysis. Depending on the varying cyanoglycoside content of the cassava varieties, the cyanide concentration in the wastewater was as high as 200 mg/l. To simulate anaerobic stabilization, a wastewater with a chemical oxygen demand (COD) of about 20 g/l was prepared from cassava roots and was fermented in a fixed-bed methanogenic reactor. The start-up phase for a 99% degradation of low concentrations of cyanide (10 mg/l) required about 6 months. After establishment of the biofilm, a cyanide concentration of up to 150 mg CN⁻/l in the fresh wastewater was degraded during anaerobic treatment at a hydraulic retention time of 3 days. All nitrogen from the degraded cyanide was converted to organic nitrogen by the biomass of the effluent. The cyanide-degrading biocoenosis of the anaerobic reactor could tolerate shock concentrations of cyanide up to 240 mg CN⁻/l for a short time. Up to 5 mmol/l NH₄Cl (i.e. 70 mg N/l = 265 mg NH₄Cl/l) in the fresh wastewater did not affect cyanide degradation. The bleaching agent sulphite, however, had a negative effect on COD and cyanide removal. For anaerobic treatment, the maximum COD space loading was 12 g l⁻¹ day⁻¹, equivalent to a hydraulic retention time of 1.8 days. The COD removal efficiency was around 90%. The maximum permanent cyanide space loading was 50 mg CN⁻ l⁻¹ day⁻¹, with tolerable shock loadings up to 75 mg CN⁻ l⁻¹day⁻¹. Under steady-state conditions, the cyanide concentration of the effluent was lower than 0.5 mg/l. Received: 15 August 1997 / Received revision: 10 October 1997 / Accepted: 14 October 1997     

The effect of low temperature (5–29 °C) and adaptation on the methanogenic activity of biomass

The influence of low temperature (5–29 °C) on the methanogenic activity of non-adapted digested sewage sludge and on temperature/leachate-adapted biomass was assayed by using municipal landfill leachate, intermediates of anaerobic degradation (propionate) and methane precursors (acetate, H₂/CO₂) as substrates. The temperature dependence of methanogenic activity could be described by Arrhenius-derived models. However, both substrate and adaptation affected the temperature dependence. The adaptation of biomass in a leachate-fed upflow anaerobic sludge-blanket reactor at approximately 20 °C for 4 months resulted in a sevenfold and fivefold increase of methanogenic activity at 11 °C and 22 °C respectively. Both acetate and H₂/CO₂ were methanized even at 5 °C. At 22 °C, methanogenic activities (acetate 4.8–84 mM) were 1.6–5.2 times higher than those at 11 °C. The half-velocity constant (K _s) of acetate utilization at 11 °C was one-third of that at 22 °C while a similar K _i was obtained at both temperatures. With propionate (1.1–5.5 mM) as substrate, meth‐anogenic activities at 11 °C were half those at 22 °C. Furthermore, the residual concentration of the substrates was not dependent on temperature. The results suggest that the adaptation of biomass enables the achievement of a high treatment capacity in the anaerobic process even under psychrophilic conditions. Received: 23 December 1996 / Received last revision: 18 June 1997 / Accepted: 23 June 1997     

Effect of feed composition and upflow velocity on aggregate characteristics in anaerobic upflow reactors

Two upflow anaerobic hybrid reactors treated lactose and a mixture of ethanol, propionate and butyrate, respectively, at a volumetric loading rate of 3.7 kg chemical oxygen demand (COD) m⁻³day⁻¹, a hydraulic retention time of 5 days and a liquid upflow velocity of 0.01 m/h. Under steady-state conditions, the lactose-fed sludge had much higher (20%–100%) specific methanogenic conversion rates than the volatile-fatty acid␣(VFA)/ethanol-fed sludge for all substrates tested, including VFA. In both reactors, a flocculant sludge developed, although a much higher content of extracellular polysaccharide was measured in the lactose-fed sludge [1900 μg compared to 305 μg uronic acid/g volatile suspended solids (VSS)]. When the liquid upflow velocity of a third, VFA/ethanol-fed reactor was increased to 0.5 m/h, granulation of the sludge occurred, accompanied by a large increase (200%–500%) in the specific methanogenic conversion rates for the syntrophic and methanogenic substrates studied. Granulation reduced the susceptibility of the sludge to flotation. Glucose was degraded at a high rate (100 mg glucose gVSS⁻¹h⁻¹) by the sludge from the third reactor, despite not having been exposed to a sugar-containing influent for 563␣days. Received: 7 June 1996 / Received revision: 23 September 1996 / Accepted: 29 September 1996     

Hydrogen production with high yield and high evolution rate by self-flocculated cells of Enterobacter aerogenes in a packed-bed reactor

Continuous hydrogen gas evolution by self-flocculated cells of Enterobacter aerogenes, a natural isolate HU-101 and its mutant AY-2, was performed in a packed-bed reactor under glucose-limiting conditions in a minimal medium. The flocs that formed during the continuous culture were retained even when the dilution rate was increased to 0.9 h⁻¹. The H₂ production rate increased linearly with increases in the dilution rate up to 0.67 h⁻¹, giving maximum H₂ production rates of 31 and 58 mmol l⁻¹ h⁻¹ in HU-101 and AY-2 respectively, at a dilution rate of more than 0.67 h⁻¹. The molar H₂ yield from glucose in AY-2 was maintained at about 1.1 at dilution rates between 0.08 h⁻¹ and 0.67 h⁻¹, but it decreased rapidly at dilution rates more than 0.8 h⁻¹. Received: 27 August 1997 / Received revision: 11 November 1997 / Accepted: 14 December 1997     

Production of 1,3-propanediol by Clostridium butyricum in continuous culture with cell recycling

The continuous fermentation of 1,3-propanediol from glycerol by Clostridium butyricum was subjected to cell recycling by filtration using hollow-fibre modules made from polysulphone. The performance of the culture system was checked at a retention ratio (dilution rate/bleed rate) of 5, dilution rates between 0.2 h⁻¹ and 1.0 h⁻¹ and glycerol input concentrations of 32 g l⁻¹ and 56 g l⁻¹. The near-to-optimum propanediol concentration of 26.5 g l⁻¹ (for 56 g l⁻¹ glycerol) was maintained up to a dilution rate of 0.5 h⁻¹ and then decreased while the propanediol productivity was highest at 0.7 h⁻¹. The productivity could be increased by a factor of four in comparison to the continuous culture without cell recycling. By application of the model of Zeng and Deckwer [(1995) Biotechnol Prog 11: 71–79] for cultures under substrate excess, it was shown that the limitations resulted exclusively from product inhibition and detrimental influences from the cell recycling system, such as shear stress, were not involved. Received: 20 October 1997 / Received revision: 12 December 1997 / Accepted: 14 December 1997     

Inhibition of methane production from whey by heavy metals – protective effect of sulfide

A whey solution was used as a substrate for methane production in an anaerobic fixed-bed reactor. At a hydraulic retention time of 10 days, equivalent to a space loading of 3.3 kg (m³day)⁻¹, 90% of the chemical oxygen demand was converted to biogas. Only a little propionate remained in the effluent. Toxicity tests with either copper chloride, zinc chloride or nickel chloride were performed on effluent from the reactor. Fifty per cent inhibition of methanogenesis was observed in the presence of ≥10 mg CuCl₂ l⁻¹≥40 mg ZnCl₂ l⁻¹ and ≥60 mg NiCl₂ l⁻¹, respectively. After exposure to Cu²⁺, Zn²⁺ or Ni²⁺ ions for 12 days, complete recovery of methanogenesis by equimolar sulfide addition was possible upon prolonged incubation. Recovery failed, however, for copper chloride concentrations ≥40 mg l⁻¹. If the sulfide was added simultaneously with the three heavy metal salts, methanogenesis was only slightly retarded and the same amount of methane as in non-inhibited controls was reached either 1 day (40 mg ZnCl₂ l⁻¹) or 2 days later (10 mg CuCl₂ l⁻¹). Up to 60 mg NiCl₂ l⁻¹ had no effect if sulfide was present. Sulfide presumably precipitated the heavy metals as metal sulfides and by this means prevented heavy metal toxicity. Received: 8 October 1999 / Received revision: 3 January 2000 / Accepted: 4 January 2000     

Growth-associated production of poly(hydroxybutyric acid) by Azotobacter beijerinckii from organic nitrogen substrates

Poly(hydroxybutyric acid) (PHB) was produced by a selectant of Azotobacter beijerinckii in media containing only organic nitrogen sources such as N substrates. The chosen compounds were casein peptone, yeast extract, casamino acids and urea, each combined with carbon substrates glucose or sucrose. The PHB was synthesized under growth-associated conditions. The concentrations amounted to more than 50% of cell dry mass on casein peptone/glucose as well as urea/glucose medium within 45 h fermentation time. Corresponding to these yields, productivities of about 0.8 g PHB l⁻¹ h⁻¹ were discovered. The highest values increased to 1.06 g PHB l⁻¹ h⁻¹ on casein peptone/glucose medium and 1.1 g PHB l⁻¹ h⁻¹ on yeast extract/glucose medium after a period of 20 h. It was found that oxygen limitation was essential for successful product formation, as demonstrated earlier. These data from basic research may support further investigations into the use of technical proteins from renewable sources as substrates for PHB production by a strain of A. beijerinckii. Received: 3 June 1997 / Received revision: 29 August 1997 / Accepted: 15 September 1997     

High rates of microbial sulphate reduction in a mesophilic ethanol-fed expanded-granular-sludge-blanket reactor

In a mesophilic (30–35 °C), sulphidogenic, ethanol-fed expanded-granular-sludge-blanket reactor, sulphate, at loading rates of up to 10.0–12.0 g Sl⁻¹␣day⁻¹, was removed with an average efficiency of more than 80%. The pH was between 7.7 and 8.3 and the maximal total dissolved sulphide concentration was up to 20 mM S (650 mg S/l). The alkaline pH was maintained by either a pH-control unit with sodium hydroxide or by stripping part of the sulphide and CO₂ from the recycle with nitrogen gas. The superficial upstream liquid velocity (v _up) was 3.0–4.5 m/h. The ratio of ethanol to sulphur was near stoichiometry. At alkaline pH, the activity of the acetotrophic sulphate-reducing bacteria, growing on acetate, was strongly enhanced, whereas at pH below 7.7 the acetotrophic sulphate-reducing bacteria were inhibited by aqueous H₂S. With regard to the removal efficiency and operational stability, external stripping with N₂ and pH control were equally successful. Received: 2 December 1996 / Received revision: 13 March 1997 / Accepted: 15 March 1997     

The effect of growth conditions on the biodegradation of tributyl phosphate and potential for the remediation of acid mine drainage waters by a naturally-occurring mixed microbial culture

The biodegradation of tributyl phosphate (Bu₃-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu₃-P biodegradation by growing cells is described. Growth at the expense of Bu₃-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu₃-P biodegradation was optimal at 30 °C, reduced at 20 °C and negligible at 4 °C and 37 °C. Incorporation of Cu or Cd inhibited, and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu₃-P biodegradation significantly, but nitrate had no effect. Sulphate (10–100 mM) was inhibitory. When pregrown biomass was used the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 μmol h⁻¹ mg protein⁻¹ and 37 μmol h⁻¹ mg protein⁻¹ respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate precipitation at the expense of Bu₃-P hydrolysis in the presence of 35 mM SO₄ ²⁻. At pH 4.5, 79% of the UO₂ ²⁺ was removed at a flow rate of 1.4 ml/h on a 7-ml test column. Received: 2 June 1997 / Received revision: 15 September 1997 / Accepted: 19 September 1997     

The diversion of lactose carbon through the tagatose pathway reduces the intracellular fructose 1,6-bisphosphate and growth rate of Streptococcus bovis

Twenty strains of Streptococcus bovis grew more slowly on lactose (1.21 ± 0.12 h⁻¹) than on glucose (1.67 ± 0.12 h⁻¹), and repeated transfers or prolonged growth in continuous culture (more than 200 generations each) did not enhance the growth rate on lactose. Lactose transport activity was poorly correlated with growth rate, and slow growth could not be explained by the ATP production rate (catabolic rate). Batch cultures growing on lactose always had less␣intracellular fructose 1,6-bisphosphate (Fru1,6P ₂) than cells growing on glucose (6.6 mM compared to 16.7 mM), and this difference could be explained by the pathway of carbon metabolism. Glucose and the glucose moiety of lactose were metabolized by the Embden-Meyerhoff-Parnas (EMP) pathway, but the galactose moiety of lactose was catabolized by the tagatose pathway, a scheme that by-passed Fru1,6P ₂. A mutant capable of co-metabolizing lactose and glucose grew more rapidly when glucose was added, even though the total rate of hexose fermentation did not change. Wild-type S. bovis grew rapidly with galactose and melibiose, but these galactose-containing sugars were activated by galactokinase and catabolized via EMP. On the basis of these results, rapid glycolytic flux through the EMP pathway is needed for the rapid growth (more than 1.2 h⁻¹) of S.␣bovis. Received: 3 June 1997 / Received revision: 10 September 1997 / Accepted: 6 January 1998     

Hollow-fibre bioreactors compared to batch and chemostat culture for the production of a recombinant toxoid by a marine Vibrio

Bioreactor selection is important for maximising the productivity of recombinant organisms. In this paper a comparison is made between growth and recombinant protein synthesis in three types of bioreactor containing a marine Vibrio capable of heterologous expression and secretion of the non-toxic B-subunit pentamer of Escherichia coli heat-labile enterotoxin, EtxB. The heterologous gene was located on the plasmid pMMB68. Resistance to carbenicillin was used to select for plasmid-containing cells. In batch and continuous culture, volumetric productivities were highest when cells were grown in the presence of carbenicillin. Without antibiotic selection, the highest volumetric productivity (9.4 mg EtxB⁻¹ h⁻¹) was observed in hollow-fibre bioreactors, and the production phase could be maintained for over 50 h. The highest specific productivity under these conditions was found in batch culture, but the maximal production phase was only of 5 h duration. In hollow-fibre reactors the type of fibre used significantly affected productivity, both with regards to the maintenance of reactor integrity and by allowing passage of the recombinant toxoid through the selectively permeable membrane. Where contamination of the product with carbenicillin is to be avoided, these bioreactors are superior to batch or continuous culture. Received: 29 January 1997 / Received revision: 9 April 1997 / Accepted: 13 April 1997     

Arctic Sea ice biota: design and evaluation of a mesocosm experiment

A mesocosm experiment (enclosure volume 220 l) was designed such that sea ice inhabited by Arctic Sea ice organisms was formed and maintained under natural conditions at 66°N in Rovaniemi, Finland. The experiment was run from natural freezing in December 1994 to melting in April 1995. The ice was inhabited by diatoms, chlorophyceae, heterotrophic flagellates, ciliates, nematodes and turbellarians. Biomass in the ice, expressed as Chlorophyll a concentration, was 20–110 μg l⁻¹; total cell densities varied from 5 × 10⁶ to 35 × 10⁶ cells l⁻¹. Amongst phototrophic organisms, a succession from a flagellate-dominated community (Chlamydomonas sp.) to a multi-species diatom-dominated community was observed. Typical Arctic species such as Nitzschia frigida and Melosira arctica were present in the ice. Bacterial concentration varied between 2 × 10⁸ and 7 × 10⁸ cells l⁻¹. At least two trophic levels were present in the ice. Received: 3 April 1997 / Accepted: 9 September 1997     

Physiology and kinetics of trimethylamine conversion by two methylotrophic strains in continuous cultivation systems

The change of dilution rate (D) on both Methylophilus methylotrophus NCIMB11348 and Methylobacterium sp. RXM CCMI908 growing in trimethylamine (TMA) chemostat cultures was studied in order to assess their ability to remove odours in fish processing plants. M. methylotrophus NCIMB11348 was grown at dilution rates of 0.012–0.084 h⁻¹ and the biomass level slightly increased up to values of D around 0.07 h⁻¹. The maximum cell production rate was obtained at 0.07 h⁻¹ corresponding to a maximum conversion of carbon into cell mass (35%). The highest rate of TMA consumption was 3.04 mM h⁻¹ occurring at D=0.076 h⁻¹. Methylobacterium sp. RXM CCMI908 was grown under similar conditions. The biomass increased in a more steep manner up to values of D around 0.06 h⁻¹. The maximum cell production rate (0.058 g l⁻¹h⁻¹) was obtained in the region close to 0.06 h⁻¹ where a maximum conversion of the carbon into cell mass (40%) was observed. The maximum TMA consumption was 2.33 mM h⁻¹ at D=0.075 h⁻¹. The flux of carbon from TMA towards cell synthesis and carbon dioxide in both strains indicates that the cell is not excreting products but directing most of the carbon source to growth. Carbon recovery levels of approximately 100% show that the cultures are carbon-limited. Values for theoretical maximum yields and maintenance coefficients are presented along with a kinetic assessment based on the determination of the substrate saturation constant and maximum growth rate for each organism. Received: 25 February 1999 / Received revision: 14 May 1999 / Accepted: 17 May 1999     

Mesophilic and thermophilic anaerobic digestion of source-sorted organic wastes: effect of ammonia on glucose degradation and methane production

The wet organic fraction of household wastes was digested anaerobically at 37 °C and 55 °C. At both temperatures the volatile solids loading was increased from 1 g l⁻¹ day⁻¹ to 9.65 g l⁻¹ day⁻¹, by reducing the nominal hydraulic retention time from 93 days to 19 days. The volatile solids removal in the reactors at both temperatures for the same loading rates was in a similar range and was still 65% at 19 days hydraulic retention time. Although more biogas was produced in the thermophilic reactor, the energy conservation in methane was slightly lower, because of a lower methane content, compared to the biogas of the mesophilic reactor. The slightly lower amount of energy conserved in the methane of the thermophilic digester was presumably balanced by the hydrogen that escaped into the gas phase and thus was no longer available for methanogenesis. In the thermophilic process, 1.4 g/l ammonia was released, whereas in the mesophilic process only 1 g/l ammonia was generated, presumably from protein degradation. Inhibition studies of methane production and glucose fermentation revealed a K _i (50%) of 3 g/l and 3.7 g/l ammonia (equivalent to 0.22 g/l and 0.28 g/l free NH₃) at 37 °C and a K _i (50%) of 3.5 g/l and 3.4 g/l ammonia (equivalent to 0.69 g/l and 0.68 g/l free NH₃) at 55 °C. This indicated that the thermophilic flora tolerated at least twice as much of free NH₃ than the mesophilic flora and, furthermore, that the thermophilic flora was able to degrade more protein. The apparent ammonia concentrations in the mesophilic and in the thermophilic biowaste reactor were low enough not to inhibit glucose fermentation and methane production of either process significantly, but may have been high enough to inhibit protein degradation. The data indicated either that the mesophilic and thermophilic protein degraders revealed a different sensitivity towards free ammonia or that the mesophilic population contained less versatile protein degraders, leaving more protein undegraded. Received: 26 March 1997 / Received revision: 13 May 1997 / Accepted: 19 May 1997     

Initiation of [36Cl]hexachlorobenzene dechlorination in three different soils under artificially induced anaerobic conditions

The potential for reductive dechlorination of hexachlorobenzene was investigated in samples of three different, naturally oxic soils held under conditions of high oxygen deficiency. The soils were water-saturated and the influence on dechlorination of adding different electron donors, a surfactant and an anaerobic microbial consortium was tested. The influence of supplied electron donors seems to depend on the organic matter content of the soils. Dechlorination in the organic-matter-rich soil from Maulach was not affected by amendment with organic electron donors. A release of about 40% chloride within 140 days was observed for this soil in all biotic-treated assays. By contrast, the organic-matter-poor soil of Eppingen showed no dechlorination in unamended assays. However, when it was supplemented with organic electron donors dechlorination of 2%–37% occurred within 140 days, depending on the type of electron donor. Complex substrate (wheat strawdust), from which carbon is slowly liberated, gave the best results. These two soils had an indigenous dechlorinating anaerobic microflora, whereas the third soil (Rastatt) required inoculation with an anaerobic consortium for dechlorination. The addition of electron donors alone did not cause dechlorination in this sandy soil. The addition of a surfactant (Tween 80) to increase the bioavailability of hexachlorobenzene did not enhance dechlorination. This process was not inhibited by inherent alternative electron acceptors in soil (NO³⁻, SO₄ ²⁻, Fe³⁺). The dechlorination did not require methanogenic conditions. Received: 12 December 1996 / Received revision: 14 March 1997 / Accepted: 15 March 1997     

Spatial distributions and net deposition rates of mineral elements in the elongating wheat (Triticum aestivum L.) leaf under saline soil conditions

Wheat leaf growth is known to be spatially affected by salinity. The altered spatial distribution of leaf growth under saline conditions may be associated with spatial changes in tissue mineral elements. The objective of this study was to evaluate the spatial distributions of mineral elements and their net deposition rates in the elongating and mature zones of leaf 4 of the main stem of spring wheat (Triticum aestivum L. cv. Lona) during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty loam with 0 and 120 mM NaCl. Three days after emergence of leaf 4, sampling was begun at 3 and 13 h into the 16-h light period. Spatial distributions of fresh weight (FW), dry weight (DW), and Na⁺, K⁺, Cl⁻, NO⁻ ₃, Ca²⁺, Mg²⁺, total P, and total N in the elongating and mature tissues were determined on a millimeter scale. The patterns of spatial distribution of Na⁺, Cl⁻, K⁺, NO₃ ⁻, and Ca²⁺ in the growing leaves were affected by salinity, while those of Mg²⁺, total P, and total N were not. Sodium, K⁺, Cl⁻, Ca²⁺, Mg²⁺, and total N concentrations (mmol · kg⁻¹ FW) were consistently higher at 120 mM NaCl than at 0 mM NaCl along the leaf axis from the leaf base, whereas NO₃ ⁻ concentration was lower at 120 mM NaCl. Deposition rates of all nutrients were greatest in the elongation zone. The elongation zone was the strongest sink for mineral elements in the leaf tissues. Local net deposition rates of Na⁺, Cl⁻, Ca²⁺, and Mg²⁺ (mmol · kg⁻¹ FW · h⁻¹) in the most actively elongating zone were enhanced by 120 mM NaCl, whereas for NO₃ ⁻ this was depressed. The lower supply of NO⁻ ₃ to growing leaves may be responsible for the inhibition of growth under saline conditions. Higher tissue concentrations of Na⁺ and Cl⁻ may cause ion imbalance but probably did not result in ion toxicity in the growing leaves. Potassium, Ca²⁺, Mg²⁺, total P, and total N are less plausibly responsible for the reduction in leaf growth in this study. Higher tissue K⁺ and Ca²⁺ concentrations at 120 mM NaCl are probably due to the presence of high Ca²⁺ in the soil of this study. Received: 13 March 1997 / Accepted: 9 June 1997