Optimization of compactin fermentation

A compactin producer Penicillium sp strain was isolated from soil in our screening program. The compactin-biosynthesising capacity of the strain was improved from 5 μg ml⁻¹ to 250 μg ml⁻¹ by mutation-selection method. We investigated the effect of the medium composition on compactin productivity. A central, orthogonal three-factor experimental design by Box and Wilson was used in the investigation. The results were analysed by non-linear regression analysis. The composition of the production medium was optimized according to the calculated mathematical model using the steepest ascent method. The compactin productivity was increased to 400 μg ml⁻¹ by applying this method. Received 08 October 1997/ Accepted in revised form 04 December 1997     

Pentachlorophenol biodegradation kinetics of an oligotrophic fluidized-bed enrichment culture

A fluidized-bed reactor (FBR) was used to enrich an aerobic chlorophenol-degrading microbial culture. Long-term continuous-flow operation with low effluent concentrations selected oligotrophic microorganisms producing good-quality effluent for pentachlorophenol(PCP)-contaminated water. PCP biodegradation kinetics was studied using this FBR enrichment culture. The results from FBR batch experiments were modeled using a modified Haldane equation, which resulted in the following kinetic constants: q _max = 0.41 mg PCP mg protein⁻¹ day⁻¹, K _S = 16 μg l⁻¹, K _i = 5.3 mg l⁻¹, and n = 3.5. These results show that the culture has a high affinity for PCP but is also inhibited by relatively low PCP concentrations (above 1.1 mg PCP l⁻¹). This enrichment culture was maintained over 1 year of continuous-flow operation with PCP as the sole source of carbon and energy. During continuous-flow operation, effluent concentrations below 2 μg l⁻¹ were achieved at 268 min hydraulic retention time (t _HR) and 2.5 mg PCP l⁻¹ feed concentration. An increase in loading rate by decreasing t _HR did not significantly deteriorate the effluent quality until a t _HR decrease from 30 min to 21 min resulted in process failure. Recovery from process failure was slow. Decreasing the feed PCP concentration and increasing t _HR resulted in an improved process recovery. Received: 10 October 1996 / Received revision: 21 January 1997 / Accepted: 24 January 1997     

Inhibition of Clostridium butyricum by 1,3-propanediol and diols during glycerol fermentation

1,3-Propanediol inhibition during glycerol fermentation to 1,3-propanediol by Clostridium butyricum CNCM 1211 has been studied. The initial concentration of the 1,3-propanediol affected the growth of the bacterium more than the glycerol fermentation. μ _max was inversely proportional to the initial concentration of 1,3-propanediol (0–65 g l⁻¹). For glycerol at 20 g l⁻¹, the growth and fermentation were completely stopped at an initial 1,3-propanediol concentration of 65 g l⁻¹. However, for an initial 1,3-propanediol concentration of 50 g l⁻¹ and glycerol at 70 g l⁻¹, the final concentration (initial and produced) of 1,3-propanediol reached 83.7 g l⁻¹(1.1 M), with complete consumption of the glycerol. Therefore, during the fermentation, the strain tolerated a 1,3-propanediol concentration higher than the initial inhibitory concentration (65 g l⁻¹). The addition of 1,2-propanediol or 2,3-butanediol (50 g l⁻¹) in the presence of glycerol (50–100 g l⁻¹), showed that 2-diols reduced the μ _max in a similar way to 1,3-propanediol. The measurement of the osmotic pressure of glycerol solutions, diols and diol/glycerol mixtures did not indicate any differences between these compounds. The hypothesis of diol inhibition was discussed. Taking into account the strain tolerance of highly concentrated 1,3-propanediol during fermentation, the fermentation processes for optimising production were considered. Received: 15 November 1999 / Revision received: 1 February 2000 / Accepted: 4 February 2000     

Batch and continuous cultivation of Anaerobiospirillum succiniciproducens for the production of succinic acid from whey

Batch and continuous cultivation of Anaerobiospirillum succiniciproducens were systematically studied for the production of succinic acid from whey. Addition of 2.5 g l⁻¹ yeast extract and 2.5 g l⁻¹ polypeptone per 10 g l⁻¹ whey was most effective for succinic acid production from both treated and nontreated whey. When 20 g l⁻¹ nontreated whey and 7 g l⁻¹ glucose were used as cosubstrates, the yield and productivity of succinic acid reached at the end of fermentation were 95% and 0.46 g (l h)⁻¹, respectively. These values were higher than those obtained using nontreated whey alone [93% and 0.24 g (l h)⁻¹ for 20 g l⁻¹ whey]. Continuous fermentation of A. succiniciproducens at an optimal dilution rate resulted in the production of succinic acid with high productivity [1.35 g (l h)⁻¹], high conversion yield (93%), and higher ratio of succinic acid to acetic acid (5.1:1) from nontreated whey. Received: 23 July 1999 / Received revision: 17 November 1999 / Accepted: 24 December 1999     

Simultaneous bioconversion of glucose and xylose to ethanol by Saccharomyces cerevisiae in the presence of xylose isomerase

Simultaneous isomerisation and fermentation (SIF) of xylose and simultaneous isomerisation and cofermentation (SICF) of a glucose/xylose mixture was carried out by Saccharomyces cerevisiae in the presence of xylose isomerase. The SIF of 50 g l⁻¹ xylose gave an ethanol concentration and metabolic yield of 7.5 g l⁻¹ and 0.36 g (g xylose consumed)⁻¹. These parameters improved to 13.4 g l⁻¹ and 0.40 respectively, when borate was added to the medium. The SICF of a mixture of 50 g l⁻¹ glucose and 50 g l⁻¹ xylose gave an ethanol concentration and metabolic yield of 29.8 g l⁻¹ and 0.42 respectively, in the presence of borate. Temperature modulation from 30 °C to 35 °C during fermentation further enhanced the above parameters to 39 g l⁻¹ and 0.45 respectively. The approach was extended to the bioconversion of sugars present in a real lignocellulose hydrolysate (peanut-shell hydrolysate) to ethanol, with a fairly good yield. Received: 14 May 1999 / Received revision: 27 September 1999 / Accepted: 2 October 1999     

High-efficiency induction of soybean hairy roots and propagation of the soybean cyst nematode

Cotyledon explants of 10 soybean [Glycine max (L.) Merr.] cultivars were inoculated with Agrobacterium rhizogenes strain K599 with and without binary vectors pBI121 or pBINm-gfp5-ER possessing both neomycin phosphotransferase II (nptII) and β-glucuronidase (gus) or nptII and green fluorescent protein (gfp) genes, respectively. Hairy roots were produced from the wounded surface of 54–95% of the cotyledon explants on MXB selective medium containing 200 μg ml⁻¹ kanamycin and 500 μg ml⁻¹ carbenicillin. Putative individual transformed hairy roots were identified by cucumopine analysis and were screened for transgene incorporation using polymerase chain reaction. All of the roots tested were found to be co-transformed with T-DNA from the Ri-plasmid and the transgene from the binary vectors. Southern blot analysis confirmed the presence of the 35S-gfp5 gene in the plant genomes. Transgene expression was also confirmed by histochemical GUS assay and Western blot analysis for the GFP. Attempts to induce shoot formation from the hairy roots failed. Infection of hairy roots of the soybean cyst nematode (Heterodera glycines Ichinohe)-susceptible cultivar, Williams 82, with eggs of H. glycines race 1, resulted in the development of mature cysts about 4–5 weeks after inoculation. Thus the soybean cyst nematode could complete its entire life cycle in transformed soybean hairy-root cultures expressing GFP. This system should be ideal for testing genes that might impart resistance to soybean cyst nematode. Received: 13 July 1999 / Accepted: 8 August 1999     

Organic halogen removal from chlorinated humic ground water and lake water by nitrifying fluidized-bed biomass characterised by electron microscopy and molecular methods

The dechlorinating and genotoxicity-removing activities of nitrifying fluidized-bed reactor biomass towards chlorinated organic compounds in water were shown at level below 1 ppm. The removal rates of adsorbable organic halogens were 200 μg Cl (g VS day)⁻¹ for chlorinated humic ground water and 50 μyg Cl (g VS day)⁻¹ for chlorinated lake water when studied in batch mode. In a sequenced batch mode the removal rates μg Cl (g VS day)⁻¹] were 2000 from chlorohumus, 1400–1800 from chlorophenols in chlorinated ground water, and 430–720 from chlorohumus in chlorinated lake water. Genotoxicity was removed to a large extent (60%–80%) from the chlorinated waters upon incubation with nitrifying reactor biomass. 2,6-Di-, 2,4,6-tri and 2,3,4,6-tetrachlorophenols competed with chlorinated water organohalogens for dechlorination. The dechlorination of chlorophenols and chlorohumus required no ammonia and was not prevented by inhibitors of ammonia oxidation, nitrapyrin, parathion, sodium diethyldithiocarbamate, or allylthiourea. Electron microscopical inspection of the biomass showed the dominance of clusters of bacteria resembling known nitrifying species, Nitrosomonas, Nitrobacter, and Nitrosospira. This was supported by polymerase chain reaction amplification of the biomass DNA with four different primers, revealing the presence of 16S rDNA sequences assignable to the same species. The most intensive band obtained with the Nitroso4E primer was shown to be closely related to Nitrosomonas europaea by restriction analysis. Received: 27 March 1998 / Received revision: 30 July 1998 / Accepted: 31 July 1998     

Evaluation of solid substrates for enzyme production by Coriolus versicolor, for use in bioremediation of chlorophenols in aqueous effluents

In the development of a system for the removal of chlorophenols from aqueous effluents, a range of solid substrates for the growth of Coriolus versicolor were investigated. Substrates included wood chips, cereal grain, wheat husk and wheat bran. Suitability for transformation of chlorophenols depended on laccase production by the fungus. The greatest amount of laccase (<25 Units g⁻¹ substrate) was produced on wheat husk and wheat bran over 30 days colonisation. Aqueous extracts of laccase from wheat husk and wheat bran cultures removed 100% of 2,4-dichlorophenol (50 ppm) from solution within 5 h and 75–80% of pentachlorophenol (50 ppm) within 24 h. Wheat bran was formulated into pellets with biscuit flour to provide a compact substrate for fungal immobilisation. Addition of 8–12% yeast extract to the pellets increased laccase production five-fold. Colonised pellets were added to chlorophenol solutions in 200–4000-ml bioreactors, resulting in >90% removal of chlorophenols within 100 min. Received: 10 April 2000 / Received revision: 4 July 2000 / Accepted: 10 July 2000     

The effect of complex carbon and nitrogen, salt, Tween-80 and acetate on delta-endotoxin production by a Bacillus thuringiensis subsp kurstaki

Delta-endotoxin production by a strain of Bacillus thuringiensis subsp kurstakion complex media based on crude gruel and fish meal was investigated. High proteolytic activities were concomitantly produced with the bioinsecticide. In such complex media, the repressive regulation due to readily consumed carbon sources was partially overcome. In order to improve substrate assimilation, 0.5 g L⁻¹ sodium chloride and 0.1% Tween-80 were supplemented to the production medium, increasing delta-endotoxin yields when using gruel concentrations below 59 g L⁻¹. At and beyond 75 g L⁻¹ gruel, delta-endotoxin yields were not affected in the presence of 0.5 g L⁻¹ NaCl and 0.1% Tween-80, but proteolytic activity yields were remarkably reduced. Thus, the use of sodium chloride and Tween-80 allowed reduction of the initial gruel concentration to 42 g L⁻¹ for the production of 3350 mg L⁻¹ delta-endotoxin, while it was only 3800 mg L⁻¹ with 92 g L⁻¹ gruel. Moreover, similar to 0.5 g L⁻¹ NaCl and 0.1% Tween-80, the use of 10 g L⁻¹ sodium acetate significantly improved delta-endotoxin production and also reduced the proteolytic activity to 250 U ml⁻¹. Received 05 November 1998/ Accepted in revised form 19 August 1999     

Simultaneous production of high activities of thermostable endoglucanase and β-glucosidase by the wild thermophilic fungus Thermoascus aurantiacus

The culture-medium composition was optimised, on a shake-flask scale, for simultaneous production of high activities of endoglucanase and β-glucosidase by Thermoascus aurantiacus using statistical factorial designs. The optimised medium containing 40.2 g l⁻¹ Solka Floc as the carbon source and 9 g l⁻¹ soymeal as the organic nitrogen source yielded 1130 nkat ml⁻¹ endoglucanase and 116 nkat ml⁻¹β-glucosidase activities after 264 h as shake cultures. In addition, good levels of β-xylanase (3479 nkat ml⁻¹) and low levels of filter-paper cellulase, β-xylosidase, α-l-arabinofuranosidase, β-mannanase, β-mannosidase, α-galactosidase and β-galactosidase were detected. Batch fermentation in a 5-l laboratory fermentor using the optimised medium allowed the production of 940 nkat ml⁻¹ endoglucanase and 102 nkat ml⁻¹β-glucosidase in 192 h. Endoglucanase and β-glucosidase showed optimum activity at pH 4.5 and pH 5, respectively, and they displayed optimum activity at 75 °C. Endoglucanase and β-glucosidase showed good stability at pH values 4–8 and 4–7, respectively, after a prolonged incubation (48 h at 50 °C). Endoglucanase had half-lives of 98 h at 70 °C and 4.1 h at 75 °C, while β-glucosidase had half-lives of 23.5 h at 70 °C and 1.7 h at 75 °C. Alkali-treated bagasse, steam-treated wheat straw, Solka floc and Sigmacell 50 were 66, 48.5, 33.5 and 14.4% hydrolysed by a crude enzyme complex of T. aurantiacus in 50 h. Received: 12 November 1999 / Accepted: 14 November 1999     

Toluene vapour removal in a laboratory-scale biofilter

A bench-scale biofilter with a 0.5-m high filter bed, inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, was used to study toluene removal from a synthetic waste air stream. Different sets of continuous tests were conducted at influent toluene concentrations ranging over 0.1–4.0 g m⁻³ and at superficial gas velocities ranging over 17.8–255 m h⁻¹. The maximum volumetric toluene removal rate for the biofilter (242 g m⁻³ h⁻¹) was obtained at a superficial gas velocity of 127.5 m h⁻¹ (corresponding to a residence time of 28 s) and a toluene inlet concentration of 4.0 g m⁻³. Under these operating conditions, toluene removal efficiency was only 0.238, which suggested that effective operation required higher residence times. Removal efficiencies higher than 0.9 were achieved at organic loads less than 113.7 g m⁻³ h⁻¹. A macro-kinetic study, performed using concentration profiles along the bioreactor, revealed this process was limited by diffusion at organic loads less than 100 g m⁻³ h⁻¹ and by biological reaction beyond this threshold. Received: 10 October 1999 / Received revision: 15 February 2000 / Accepted: 18 February 2000     

Control of salt gland activity in the hatchling green sea turtle, Chelonia mydas

 We studied the control of salt gland secretion in hatchling Chelonia mydas. The threshold salt load to activate salt secretion was between 400 μmol NaCl 100 g bodymass (BM)⁻¹ and 600 μmol NaCl 100 g BM⁻¹, which caused an increase in plasma sodium concentration of 13% to 19%. Following a salt load of 2700 μmol NaCl 100 g BM⁻¹, salt gland secretion commenced in 12 ± 1.3 min and reached maximal secretory concentration within 2–7 min. Maximal secretory rate of a single gland averaged 415 μmol Na 100 g BM⁻¹ h⁻¹. Plasma sodium concentration and total osmotic concentration after salt loading were significantly higher than pretreatment values within 2 min. Adrenalin (25 μg kg BM⁻¹) and the cholinergic agonist methacholine (1 mg kg BM⁻¹) inhibited salt gland activity. Atropine (10 mg kg BM⁻¹) reversed methacholine inhibition and stimulated salt gland secretion when administered with a subthreshold salt load. Arginine vasotocin produced a transient reduction in sodium secretion by the active gland, while atrial natriuretic factor, vasoactive intestinal peptide and neuropeptide Y had no measurable effect on any aspect of salt gland secretion. Our results demonstrated that secretion of the salt gland in C. mydas can be modified by neural and hormonal chemicals in vivo and that the cholinergic and adrenergic stimulation of an exocrine gland do not appear to have the typical, antagonist actions on the chelonian salt gland. Accepted: 28 September 1999     

Enhanced mineralization of pentachlorophenol by κ-carrageenan-encapsulated Pseudomonas sp. UG30

A pentachlorophenol(PCP)-degrading Pseudomonas sp. strain UG30 was encapsulated in κ-carrageenan for use in PCP degradation. Free and encapsulated cells were compared for their ability to dechlorinate and mineralize 100–800 μg/ml sodium pentachlorophenate in broth. Dechlorination was measured with a chloride ion electrode, and mineralization was measured by ¹⁴CO₂ evolution from radiolabelled [U-¹⁴C]PCP. Free and encapsulated Pseudomonas sp. UG30 cells mineralized up to 200 μg/ml and 600 μg/ml PCP, respectively, after 21 days. Encapsulation of UG30 cells provided a protective effect, allowing dechlorination and mineralization of high levels of PCP to occur. Received: 3 May 1996 / Received revision: 4 September 1996 / Accepted: 13 September 1996     

A heat shock following electroporation induces highly efficient transformation of Corynebacterium glutamicum with xenogeneic plasmid DNA

An improved method for the electrotransformation of wild-type Corynebacterium glutamicum (ATCC 13032) is described. The two crucial alterations to previously developed methods are: cultivation of cells used for electrotransformation at 18 °C instead of 30 °C, and application of a heat shock immediately following electrotransformation. Cells cultivated at sub optimal temperature have a 100-fold improved transformation efficiency (10⁸ cfu μg⁻¹) for syngeneic DNA (DNA isolated from the same species). A heat shock applied to these cells following electroporation improved the transformation efficiency for xenogeneic DNA (DNA isolated from a different species). In combination, low cultivation temperature and heat shock act synergistically and increased the transformation efficiency by four orders of magnitude to 2.5 × 10⁶ cfu μg⁻¹ xenogeneic DNA. The method was used to generate gene disruptions in C. glutamicum. Received: 26 March 1999 / Received revision: 9 June 1999 / Accepted: 11 June 1999     

Biological control of the zebra mussel Dreissena polymorpha and the snail Biomphalaria glabrata, using Gramicidin S and D and molluscicidal strains of Bacillus

Applications of Final Whole Culture (FWC) or primary powder material from strains of each of four Bacillus species (B. alvei, B. brevis, B. circulans, B. laterosporus) used singly, as well as the antibiotics Gramicidin S (GS) and Gramicidin D (GD) used singly, were found to be molluscicidal against several life cycle stages of the zebra mussel Dreissena polymorpha. Combinations of the bacterial material with either GS or GD were either additive (for GS) or antagonistic (for GD). The smaller the life cycle stage of the animal, the more sensitive it was to either the bacterial or antibiotic agent. The veliger stage was particularly sensitive to each agent, with the molluscicidal effect being more rapid in the veliger (5 h) than in the adult (6 days). The molluscicidal effects of these agents (at 1–100 μ g ml⁻¹) against the veliger stages of the zebra mussel were comparable to the activity of B. thuringiensis and B. sphaericus against their target organisms. These agents used singly were also active against small adult Biomphalaria glabrata, the snail vector of schistosomiasis (eg at tenths of μ g ml⁻¹ of GS). Received 09 July 1996/ Accepted in revised form 06 November 1996     

Benzene/toluene/p-xylene degradation. Part II. Effect of substrate interactions and feeding strategies in toluene/benzene and toluene/p-xylene fermentations in a partitioning bioreactor

A two-phase aqueous/organic partitioning bioreactor scheme was used to degrade mixtures of toluene and benzene, and toluene and p-xylene, using simultaneous and sequential feeding strategies. The aqueous phase of the partitioning bioreactor contained Pseudomonas sp. ATCC 55595, an organism able to degrade benzene, toluene and p-xylene simultaneously. An industrial grade of oleyl alcohol served as the organic phase. In each experiment, the organic phase of the bioreactor was loaded with 10.15 g toluene, and either 2.0 g benzene or 2.1 g p-xylene. The resulting aqueous phase concentrations were 50 mg/l, 25 mg/l and 8 mg/l toluene, benzene and p-xylene respectively. The simultaneous fermentation of benzene and toluene consumed these compounds at volumetric rates of 0.024 g l⁻¹ h⁻¹ and 0.067 g l⁻¹ h⁻¹, respectively. The simultaneous fermentation of toluene and p-xylene consumed these xenobiotics at volumetric rates of 0.066 g l⁻¹ h⁻¹ and 0.018 g l⁻¹ h⁻¹, respectively. A sequential feeding strategy was employed in which toluene was added initially, but the benzene or p-xylene aliquot was added only after the cells had consumed half of the initial toluene concentration. This strategy was shown to improve overall degradation rates, and to reduce the stress on the microorganisms. In the sequential fermentation of benzene and toluene, the volumetric degradation rates were 0.056 g l⁻¹ h⁻¹ and 0.079 g l⁻¹ h⁻¹, respectively. In the toluene/p-xylene sequential fermentation, the initial toluene load was consumed before the p-xylene aliquot was consumed. After 12 h in which no p-xylene degradation was observed, a 4.0-g toluene aliquot was added, and p-xylene degradation resumed. Excluding that 12-h period, the microbes consumed toluene and p-xylene at volumetric rates of 0.074 g l⁻¹ h⁻¹ and 0.025 g l⁻¹ h⁻¹, respectively. Oxygen limitation occurred in all fermentations during the rapid growth phase. Received: 16 November 1998 / Received revision: 29 March 1999 / Accepted: 9 April 1999     

Candida bombicola : production of novel alkyl glycosides based on glucose/2-dodecanol

Candida bombicola produces glycolipids containing sophorose and a glycosidically/esterically bound ω- or (ω−1)-hydroxy C₁₆₍₁₈₎ acid. Here we describe novel glycolipids from this source. Glucose and 2-dodecanol were used for the cultivation of the yeast, one part of the racemic secondary alcohol being connected directly with a glucose or a sophorose unit. A relatively high content of yeast extract, up to 4 g l⁻¹, and subsequently higher biomass concentrations favoured the production of novel products. The provision of 150 g l⁻¹ glucose and 15 g l⁻¹ 2-dodecanol resulted in maximum production of 22 g l⁻¹ novel alkyl glycosides (more than 90% novel products). The molecular structures were analysed by gas chromatography, fast atom bombardment/mass spectrometry, ¹H- and ¹³C-nuclear magnetic resonance and optical rotation studies. Sophorose and glucose were detected as carbohydrate moieties, (S)-(+)-2-dodecanol (88%) was found to be the major lipid moiety. The new glycolipids are suitable biosurfactants, reducing the surface tension of water from 72 mN m⁻¹ to 32–38 mN m⁻¹. Received: 8 December 1997 / Received revision: 19 March 1998 / Accepted: 20 March 1998     

Thermophilic acidification of dairy wastewater

Acidification of simulated dairy wastewater was conducted in an upflow reactor at 55 °C. Results showed that the degree of acidification decreased with the increase in chemical oxygen demand (COD) loading rate, from 60.8% at 4 g l⁻¹ day⁻¹ to 27.1% at 24 g l⁻¹ day⁻¹. Carbohydrate was readily degraded at all loading rates, but degradation of protein and lipid decreased with the increase in loading rate. Most carbohydrate degradation occurred at the reactor bottom, whereas protein was degraded mainly after the carbohydrate became depleted. The predominant acidification products were acetate, propionate, butyrate and ethanol, whereas formate, i-butyrate, valerate, i-valerate, caproate, lactate, methanol, propanol and butanol were present in lesser quantities. The increase in loading rate resulted in the increase of propionate and the decrease of acetate, but had little effect on ethanol and butyrate productions. Only 2.5–8.8% of influent COD was converted to hydrogen and methane. The biomass yield was 0.30–0.43 mg VSS mg⁻¹ COD. Received: 8 December 1999 / Received revision: 14 February 2000 / Accepted: 25 February 2000     

Rhamnose lipids – biosynthesis, microbial production and application potential

Biosurfactants containing rhamnose and β-hydroxydecanoic acid and called rhamnolipids are reviewed with respect to microbial producers, their physiological role, biosynthesis and genetics, and especially their microbial overproduction, physicochemical properties and potential applications. With Pseudomonas species, more than 100 g l⁻¹ rhamnolipids were produced from 160 g l⁻¹ soybean oil at a volumetric productivity of 0.4 g l⁻¹h⁻¹. The individual rhamnolipids are able to lower the surface tension of water from 72 mN m⁻¹ to 25–30 mN m⁻¹ at concentrations of 10–200 mg l⁻¹. After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution, removing oil from sand and in combating zoosporic phytopathogens. Rhamnolipids are also a source of l-rhamnose, which is already used for the industrial production of high-quality flavor components. Received: 1 July 1998 / Received revision: 11 September 1998 / Accepted: 13 September 1998     

Physiology of acute silver toxicity in the starry flounder (Platichthys stellatus) in seawater

Physiological effects of exposure to silver (AgCl_n ⁿ⁻¹; 250 μg Ag l⁻¹ or 1000 μg Ag l⁻¹) in seawater fish were investigated using adult starry flounders. While all fish survived up to 10 days in 250 μg Ag l⁻¹, flounders started to die after day 4 in 1000 μg l⁻¹. Dose-dependent increases in plasma and hepatic silver concentrations showed that silver was available for uptake. There were minimal negative effects on hematological parameters, acid-base status, and blood gases. Plasma ammonia showed a pronounced (three- to four-fold), but transient increase in flounders exposed to either 250 μg Ag l⁻¹ or 1000 μg Ag l⁻¹. Whole body ammonia and acid equivalent efflux measurements indicated that ammonia retention was due to a combination of stimulated production and inhibited excretion. In the 1000-μg Ag l⁻¹ group there was a similar transient increase in plasma [magnesium], which was restored by day 4. In contrast, plasma chloride and sodium levels increased gradually towards the point when fish began to die. At 250 μg Ag l⁻¹, the Na⁺/K⁺-ATPase activity of the intestine was unaffected but there was a two-fold increase in branchial Na⁺/K⁺-ATPase activity. The latter effect was interpreted as compensation for an elevated chloride and sodium load. The increases in plasma chloride and sodium concentrations were accompanied by a marked suppression of drinking, thereby indicating that acute silver toxicity was likely caused by a combination of elevated electrolyte concentrations and dehydration. Accepted: 9 June 1999