Palm oil mill effluent (POME) cultured marine microalgae as supplementary diet for rotifer culture

Malaysia is the world’s leading producer of palm oil products that contribute US$ 7.5 billion in export revenues. Like any other agro-based industries, it generates waste that could be utilized as a source of organic nutrients for microalgae culture. Present investigation delves upon Isochrysis sp. culture in POME modified medium and its utilization as a supplement to Nanochloropsis sp. in rotifer cultures. The culture conditions were optimized using a 1 L photobioreactor (Temp: 23°C, illumination: 180 ∼ 200 μmol photons m⁻²s⁻¹, n = 6) and scaled up to 10 L outdoor system (Temp: 26–29°C, illumination: 50 ∼ 180 μmol photons m⁻²s⁻¹, n = 3). Algal growth rate in photobioreactor (μ = 0.0363 h⁻¹) was 55% higher compared to outdoor culture (μ = 0.0163 h⁻¹), but biomass production was 1.3 times higher in outdoor culture (Outdoor = 91.7 mg m⁻²d⁻¹; Photobioreactor = 69 mg m⁻²d⁻¹). Outdoor culture produced 18% higher lipid; while total fatty acids (FA) was not significantly affected by the change in culture systems as both cultures yield almost similar concentrations of fatty acids per gram of sample (photobioreactor = 119.17 mg g⁻¹; outdoor culture = 104.50 mg g⁻¹); however, outdoor cultured Isochrysis sp. had 26% more polyunsaturated fatty acids (PUFAs). Rotifers cultured in Isochrysis sp./ Nanochloropsis sp. (1:1, v/v) mixture gave similar growth rate as 100% Nanochoropsis sp. culture (μ = 0.40 d⁻¹), but had 45% higher counts of rotifers with eggs (t = 7, maximum). The Isochrysis sp. culture successfully lowered the nitrate (46%) and orthophosphate (83%) during outdoor culture.     

Exchanges of oxygen, carbon dioxide, nitrogen and water in the caecilian Dermophis mexicanus

Oxygen consumption was measured in five Dermophis mexicanus and averaged (±SEM) 0.047 ± 0.004 ml O₂ g⁻¹ h⁻¹. Carbon dioxide production averaged 0.053 ± 0.005 ml CO₂ g⁻¹ h⁻¹ in the same five animals 1 week later. This metabolic rate is similar to metabolic rates of other Gymnophionans but lower than metabolic rates reported for Anurans and Urodeles. Total nitrogen excretion averaged 1.37 μmol N g⁻¹ h⁻¹ which is higher than that found for other amphibians. Of this, 82.5% (1.13 μmol N g⁻¹ h⁻¹) was in the form of urea while 17.5% (0.24 μmol N g⁻¹ h⁻¹) was in the form of NH₃ + NH⁺ ₄. Such ureotelism is typical of terrestrial amphibians like D. mexicanus. Osmotic water flux averaged 0.0193 ml g⁻¹ h⁻¹ in control (sham injected) animals and was not significantly altered by injection of either arginine vasotocin or mesotocin. This osmotic flux is similar to osmotic fluxes found for other terrestrial amphibians. The combined data suggest that metabolism in D. mexicanus is, like most other Gymnophionans, lower than other amphibians. The high rates of nitrogen (especially urea) excretion suggests that this fossorial animal accumulates urea like other burrowing amphibians. Accepted: 27 June 2000     

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     

Determination of the kinetic parameters during continuous cultivation of the lipase-producing thermophile Bacillus sp. IHI-91 on olive oil

A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 °C. Lipase activity decreased with increasing dilution rate while lipase productivity showed a maximum of 340 U l⁻¹ h⁻¹ at a dilution rate of 0.4 h⁻¹. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation of olive oil were determined. The maximal biomass output method led to a saturation constant K _S of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, μ_max, of 1.0 h⁻¹. Oxygen uptake rates of up to 2.9 g l⁻¹h⁻¹ were calculated and the yield coefficient, Y _X/O, was determined to be 0.29 g dry cell weight/g O₂. From an overall material balance the yield coefficient, Y _X/S, was estimated to be 0.60 g dry cell weight/g olive oil. Received: 8 January 1997 / Received revision: 30 April 1997 / Accepted: 4 May 1997     

Biodegradation of propanol and isopropanol by a mixed microbial consortium

The aerobic biodegradation of high concentrations of 1-propanol and 2-propanol (IPA) by a mixed microbial consortium was investigated. Solvent concentrations were one order of magnitude greater than any previously reported in the literature. The consortium utilized these solvents as their sole carbon source to a maximum cell density of 2.4 × 10⁹ cells ml⁻¹. Enrichment experiments with propanol or IPA as carbon sources were carried out in batch culture and maximum specific growth rates (μ_max) calculated. At 20 °C, μ _max values were calculated to be 0.0305 h⁻¹ and 0.1093 h⁻¹ on 1% (v/v) IPA and 1-propanol, respectively. Growth on propanol and IPA was carried out between temperatures of 10 °C and 45 °C. Temperature shock responses by the microbial consortium at temperatures above 45 °C were demonstrated by considerable cell flocculation. An increase in propanol substrate concentration from 1% (v/v) to 2% (v/v) decreased the μ _max from 0.1093 h⁻¹ to 0.0715 h⁻¹. Maximum achievable biodegradation rates of propanol and IPA were 6.11 × 10⁻³% (v/v) h⁻¹ and 2.72 × 10⁻³% (v/v) h⁻¹, respectively. Generation of acetone during IPA biodegradation commenced at 264 h and reached a maximum concentration of 0.4% (v/v). The results demonstrate the potential of mixed microbial consortia in the bioremediation of solvent-containing waste streams. Received: 14 December 1999 / Received revision: 3 April 2000 / Accepted: 7 April 2000     

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     

Factors Affecting Predation by Cyclidium sp. and Euplotes sp. on PAH-Degrading and Nondegrading Bacteria

Abstract If predators select for or against contaminant-degrading bacteria, it will affect bacterial survival and has important implications for bioremediation. Protozoa are important predators of bacteria. In order to determine whether protozoa preyed differentially on bacteria with different degradation abilities, two ciliates (Euplotes sp. and Cyclidium sp.) and three strains of PAH-degrading bacteria (Vibrio spp., degrading naphthalene, anthracene, or phenanthrene) were isolated from sediment from New York/New Jersey Harbor. By manipulating growth conditions, bacterial strains with different PAH-degradation abilities and different cell properties were produced. Stepwise regression models were used to analyze how clearance rates on suspended bacteria and grazing rates on bacteria attached to particles were affected by bacterial size, hydrophobicity, C:N ratio, protein content, and PAH-degradation ability. Clearance rates ranged from 0 to 49 nl ciliate⁻¹ h⁻¹ for Euplotes sp. and from 0 to 1.7 nl ciliate⁻¹ h⁻¹ for Cyclidium sp. Clearance rates of both ciliates were positively correlated with bacterial size, hydrophobicity, and protein content, and negatively correlated with C:N ratio. PAH degradation ability had no (for Euplotes sp.) or small (for Cyclidium sp.) effects on clearance rates. The models accounted for 63–75% of the variation in clearance rates on different bacteria. Only Euplotes sp. grazed on attached bacteria, at rates from 3 to 176 bacteria ciliate⁻¹ h⁻¹. A regression model with only C:N ratio and protein content explained 45% of the variation in grazing rates. These models indicate that multiple properties of bacteria affect their susceptibility to predation by ciliates, but PAH-degradation ability per se has little effect. Received: 5 May 1998; Accepted: 14 September 1998     

Effect of growth rate on α-amylase production by Streptomyces sp. IMD 2679

The α-amylase of Streptomyces sp. IMD 2679 was subject to catabolite repression. Four different growth rates were achieved when the organism was grown at 40 °C and 55 °C in the presence and absence of cobalt, with an inverse relationship between α-amylase production and growth rate. Highest α-amylase yields (520 units/ml) were obtained at the lowest growth rate (0.062 h⁻¹), at 40 °C in the absence of cobalt, while at the highest growth rate (0.35 h⁻¹), at 55 °C in the presence of cobalt, α-amylase production was decreased to 150 units/ml. As growth rate increased, the rate of specific utilisation of the carbon source maltose also increased, from 46 to 123 μg maltose (mg biomass)⁻¹ h⁻¹. The pattern and levels of α-glucosidase (the enzyme degrading maltose) detected intracellularly in each case, indicate that growth rate effectively controls the rate of feeding of glucose to the cell, and thus catabolite repression. Received: 17 February 1997 / Received revision: 29 April 1997 / Accepted: 11 May 1997     

Grazing Rates in Euplotes mutabilis: Relationship between Particle Size and Concentration

Abstract Grazing behavior of both individual cells and populations of the marine hypotrich Euplotes mutabilis, a largely benthic ciliate that feeds on suspended particles, was studied using fluorescent latex microspheres. Microspheres of sizes 0.57-, 1.90-, 3.06-, 5.66-, and 10.0-μm diam were offered at concentrations from 10² to 10⁶ ml⁻¹. Their uptake in a ten-min period was determined. Food particles within such ranges of size and concentration are found under natural conditions. The ciliates ingested particles of all sizes offered. Uptake rates at all concentrations were dependent upon particle size, with 1.90- and 3.06-μm diam microspheres having the highest uptake rate in all cases. For all sizes, there was an increase in the percentage of feeding cells and in the uptake rate (the number of particles ingested cell⁻¹ h⁻¹), with increasing particle concentration. When uptake was expressed as the volume ingested, maximum values were obtained for 5.85-μm diam microspheres at a concentration of 10⁶ ml⁻¹. By taking a small number of large particles, present at a low concentration in the medium, a ciliate can ingest a greater biovolume than by taking a high number of small particles which are abundant in the medium. These results demonstrate that some ciliates can graze particles of a wide range of sizes. Also, its nutrition can be affected by changing ambient concentrations of different prey, both through effects on the proportion of feeding cells and through the relative food content of the particles. The data can also add to the understanding of food niche partitioning between species. At low particle concentrations, particularly, it is important to consider the behavior of individual ciliates as well as of the whole population. Received: 11 February 1997; Accepted: 21 October 1997     

The viability to a wall shear stress and propagation of <Emphasis Type="Italic">Bifidobacterium longum</Emphasis> in the intensive membrane bioreactor

Bifidobacterium longum grew at 65 L pilot scale of the membrane bioreactor (MBR), externally fitted with ceramic membrane (0.7 m²). Cell mass at the MBR reached 22.18 g L⁻¹ as dry cell weight in 12 h, which is 8.44 times higher than cell mass attained at the vial culture. The growth rate in the vial culture was μ = 0.385 h⁻ and at the batch culture was μ = 1.13 h⁻ in the exponential period and μ = 0.31 h⁻¹ in the stationary period. In the fed-batch mode was μ = 1.102 h⁻¹ for 6 h with inoculation and declined to μ = 0.456 h⁻¹ with feeding of feed medium. The growth rate at the MBR was μ = 0.134 h⁻¹. The number of viable cells was 6.01 × 10¹² cfu L⁻¹ at the batch culture, but increased to 1.15 × 10¹⁴ cfu L⁻¹ at the MBR culture. The specific growth rate of viable cell number (colony-forming units per liter, per hour) improved by 6.01 times from the batch to the MBR culture. The wall shear stress mainly generated by the pump, and the membrane incorporated into the MBR was controlled during the cultivation at the MBR. The viability of B. longum declined to under 10% in the first 2 weeks of the 4-week stability test (40°C) as B. longum was exposed to over wall shear stress 713 Pa, but the viability improved to 30–40% in wall shear stress of 260 Pa or STR culture. The loss in the cell viability can be saved by managing with wall shear stress during the cultivation at the MBR.     

Particle size effects in bioleaching of pyrite by acidophilic thermophile Sulfolobus metallicus (BC)

The effect of mineral particle size on the bioleaching of pyrite by the acidophilic thermophile Sulfolobus metallicus was investigated in a batch bioreactor. Decreasing the particle size from a mean diameter of 202 micron (size fraction: 150–180 micron) to a mean diameter of 42.5 micron (size fraction: 25–45 micron) enhanced the bioleaching rate from 0.05 kg m⁻³ h⁻¹ to 0.098 kg m⁻³ h⁻¹. The particle size distribution of the mineral in this range did not influence the morphology and growth kinetics of the cells. The values of specific growth rate (μ) and yield factor (Y) were 0.018–0.025 h⁻¹ and 0.67 × 10¹¹–1.45 × 10¹¹ cells (g iron)⁻¹, respectively. Decreasing the particle size of the mineral to a mean diameter of 6.40 micron (size fraction <25 micron) adversely influenced the activity of the cells. The presence of fine particles apparently damaged the structure of the cells, resulting in their inability to oxidise pyrite. Received: 11 December 1998 / Accepted: 9 April 1999     

Microbial biodegradation of organic wastes containing surfactants in a continuous-flow reactor

In a continuous flow bioreactor seeded with microbes from municipal activated sludge, complete organic carbon oxidation of simulated graywater (wastewater produced in human residences, excluding toilet wastes) was achieved at dilution rates up to 0.36 h⁻¹ in the presence of 64.1 μ M linear alkylbenzenesulfonate (LAS) L⁻¹. At LAS concentrations of 187 μ M, the system functioned only at dilution rates up to 0.23 h⁻¹, and the biomass yield was two-fold lower. There were physiological changes in the microbial communities under different operating conditions, as measured by specific contents of ATP and extracellular hydrolases as well as the respiratory potential of the biomass. LAS inhibited the activity of LAS-degrading microbes at >150  μ M LAS, and the activity of other microbes at >75 μ M LAS. Chemical analysis of graywater indicated that samples consisted primarily of biological polymers (proteins and polysaccharides) and lower concentrations of surfactants. Biological remediation of graywater is possible, although treatment efficiency is influenced by the operating conditions and wastestream composition. Received 08 July 1996/ Accepted in revised form 14 November 1996     

The relative importance of tryptophan-dependent and tryptophan-independent biosynthesis of indole-3-acetic acid in tobacco during vegetative growth

A quantitative study of indole-3-acetic acid (IAA) turnover, and the contribution of tryptophan-dependent and tryptophan-independent IAA-biosynthesis pathways, was carried out using protoplast preparations and shoot apices obtained from wild-type and transgenic, IAA-overproducing tobacco (Nicotiana tabacum L.) plants, during a phase of growth when the level of endogenous IAA was stable. Based on the rate of disappearance of [¹³C₆]IAA, the half-life of the IAA pool was calculated to be 1.1 h in wild-type protoplasts and 0.8 h in protoplasts from the IAA-overproducing line, corresponding to metabolic rates of 59 and 160 pg IAA (μg Chl)⁻¹ h⁻¹, respectively. The rate of conversion of tryptophan to IAA was 15 pg IAA (μg Chl)⁻¹ h⁻¹ in wild-type protoplasts and 101 pg IAA (μg Chl)⁻¹ h⁻¹ in protoplasts from IAA-overproducing plants. In both instances, IAA was metabolised more rapidly than it was synthesised from tryptophan. As the endogenous IAA pools were in a steady state, these findings indicate that IAA biosynthesis via the tryptophan-independent pathway was 44 pg IAA (μg Chl)⁻¹ h⁻¹ and 59 pg IAA (μg Chl)⁻¹ h⁻¹, respectively, in the wild-type and transformed protoplast preparations. In a parallel study with apical shoot tissue, the presumed site of IAA biosynthesis, the rate of tryptophan-dependent IAA biosynthesis exceeded the rate of metabolism of [¹³C₆]IAA despite the steady state of the endogenous IAA pool. The most likely explanation for this anomaly is that, unlike the protoplast system, injection of substrates into the apical tissues did not result in uniform distribution of label, and that at least some of the [²H₅]tryptophan was metabolised in compartments not normally active in IAA biosynthesis. This demonstrates the importance of using experimental systems where labelling of the precursor pool can be strictly controlled. Received: 18 January 2000 / Accepted 24 February 2000     

Biodegradation kinetics of monoterpenes in liquid and soil-slurry systems

Batch experiments were conducted to evaluate the biodegradation rates of limonene, α-pinene, γ-terpinene, terpinolene and α-terpineol at 23 °C under aerobic conditions. Biodegradation was demonstrated by the depletion of monoterpene mass, CO₂ production and a corresponding increase in biomass. Monoterpene degradation in liquid cultures devoid of soil followed Monod kinetics. The maximum specific growth rate (μ_max) was 0.02 h⁻¹ and 0.06 h⁻¹ and the half-velocity constant (K _s ) varied from 32 mg/l to 3 mg/l for the limonene and α-terpineol respectively. The recovery of monoterpenes by solvent extraction from autoclaved and azide-amended soil-slurry samples decreased over time and ranged from 69% to 73% for 120 h of incubation period. Although a significant fraction of monoterpene hydrocarbon could not be extracted, mineralization of these compounds in the soil-slurry systems took place, as shown by CO₂ production. The soil-normalized degradation rates for the hydrocarbon monoterpenes ranged from 0.6 μg g⁻¹ h⁻¹ to 2.1 μg g⁻¹ h⁻¹. A kinetic model – which combined monoterpene biodegradation in the liquid phase and net desorption – was developed and applied to data obtained from soil-slurry assays. Received: 10 September 1996 / Received revision: 16 December 1996 / Accepted: 10 January 1997     

Protozoan growth rates in Antarctic lakes

The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057–0.384 h⁻¹), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific growth rates than HNAN (0.0029–0.0059 h⁻¹ and 0.0056–0.0127 h⁻¹, respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and 0.150 h⁻¹ for heterotrophic ciliates, 0.0143 h⁻¹ for a mixotrophic Plagiocampa species and 0.0075 h⁻¹ for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable growth rates seen within and between Antarctic lakes. Accepted: 7 December 1999     

Urea decomposing activity of fractionated brackish phytoplankton in Lake Nakaumi

The influence of brackish phytoplankton cell classes upon the response of urea decomposition was investigated in Lake Nakaumi. The urea decomposition rate was 5 to 350 μmol urea m⁻³ h⁻¹ in the light and 3 to 137 μmol urea m⁻³ h⁻¹ in the dark. The urea decomposition rates in the light were obviously higher than in the dark. An extremely high rate (350 μmol urea m⁻³ h⁻¹) was observed in Yonago Bay. The rate in the smaller fraction (<5 μm) exceeded that in the middle (5–25 μm) and larger fractions (>25 μm). The chlorophyll- and photosynthesis-specific rates for urea decomposition in the light were 0.5 to 3.9 μmol urea mg chl.a ⁻¹ h⁻¹ and 0.3 to 1.3 μmol urea mg photo.C⁻¹. The specific urea decomposing activities were higher in the smaller fraction than in the other two fractions. The present results suggest that in brackish waters urea decomposition occurred with coupling to the standing crop and photosynthetic activity of phytoplankton. Received: May 22, 1999 / Accepted: August 15, 1999     

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     

Effects of reduced diameter of bag cultures on content of essential fatty acids and cell density in a continuous algal production system

Cell density and fatty acid (FA) content of Pavlova lutheri and Chaetoceros muelleri were analysed in a continuous algal production system (250-L bags) with reduced diameter. The cell density and FA content and composition in the algal production system were determined in replicate bags over a period of 5 weeks. The results showed that the cell density and essential FAs increased during the experiment for both species. After 5 weeks the mean cell numbers had increased to 6.0 ± 0.3 × 10⁶ cells mL⁻¹ in the P. lutheri bags and 6.0 ± 0.4 × 10⁶ cells mL⁻¹ in the C. muelleri bags. The content of total FAs increased significantly (p < 0.05) in all of the bags during the experiment. At the end of the experiment the mean total FA content were 2.7 ± 0.3 pg cell⁻¹ in the P. lutheri bags and 1.8 ± 0.1 pg cell⁻¹ in the C. muelleri bags. Maximum total FA content registered was 3.0 pg cell⁻¹ in one of the P. lutheri bags. The content of the essential FAs (ARA, EPA, DHA) increased over time in both of the species. At the end of the experiment the content of EPA (0.6 ± 0.1 pg cell⁻¹) and DHA (0.3 ± 0.0 pg cell⁻¹) were highest in the P. lutheri bags, while ARA (0.1 ± 0.0 pg cell⁻¹) was highest in C. muelleri. EPA and DHA constituted 22% and 11%, respectively, of total FA content in P. lutheri, while ARA constituted 6% of total FA content in C. muelleri. The results from this experiment indicate that flagellates such as P. lutheri perform better in narrow bags with improved light conditions, while diatoms like C. muelleri perform better in wider bags under light limitation. Implications for bivalve hatcheries are discussed.     

Structural and functional properties of sympagic communities in the annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

Studies on the chemical and biological properties of annual pack ice at a coastal station in Terra Nova Bay (74°41.72′S, 164°11.63′E) were carried out during austral spring at 3-day intervals from 5 November to 1 December 1997. Temporal changes of nutrient concentrations, algal biomasses, taxonomic composition, photosynthetic pigment spectra and P–E relationships were studied. Quantity, composition and degradation rates of organic matter in the intact sea ice were also investigated. In addition, microcosm experiments were carried out to evaluate photosynthetic and photo-acclimation processes of the sympagic flora in relation to different light regimes. High concentrations of ammonia were measured in four ice-cores (weighted mean values of the cores ranged from 4.3 ± 1.9 μM to 7.2 ± 3.4 μM), whereas nitrate and phosphate displayed high concentrations (up to 35.9 μM and 7.6 μM, respectively) only in the bottom layer (135–145 cm depth). Particulate carbohydrate and protein concentrations in the intact sea ice ranged from 0.5 to 2.3 mg l⁻¹ and 0.2 to 2.0 mg l⁻¹, respectively, displaying a notable accumulation of organic matter in the bottom colored layer, where bacterial enzymatic activities also reached the highest values. Aminopeptidase activity was extremely high (up to 19.7 μM l⁻¹ h⁻¹ ± 0.05 in the bottom layer), suggesting a rapid turnover rate of nitrogen–enriched organic compounds (e.g. proteins). By contrast, bacterial secondary production was low, suggesting that only a very small fraction of mobilized organic matter was converted into bacterial biomass (<0.01‰). The sympagic autotrophic biomass (in terms of chlorophaeopigments) of the bottom layer was high, increasing during the sampling period from 680 to 2480 μg l⁻¹. Analyses of pigments performed by HPLC, as well as microscope observations, indicated that diatoms dominated bottom communities. The most important species were Amphiprora sp. and Nitschia cfr. stellata. Bottom sympagic communities showed an average P ^B _max of 0.12 mgC mg Chl⁻¹ and low photoadaptation index (E _k=18 μE m⁻² s⁻¹, E _m=65 μE m⁻² s⁻¹). Results of the microcosm experiment also indicated that communities were photo-oxidized when irradiance exceeded 100 μE m⁻² s⁻¹. This result suggests that micro- autotrophs inhabiting sea ice might have a minor role in the pelagic algal blooms. Accepted: 4 August 1999     

Bioreactor for continuous synthesis of compactin by Penicillium cyclopium

Compactin was synthesized by Penicillium cyclopium in submerged as well as in bioreactor systems and assayed spectrophotometrically with a detection limit of 0.5 μg ml⁻¹ solvent. Synthesis in submerged culture was affected by aeration, glucose level, pH, and type and molarity of buffer. Citrate or succinate (pH 4.0, 0.10 M) in malt glucose peptone broth (MGPB) stimulated cell specialization, sporulation, enhanced compactin permeation from mycelia and its production (60.05 μg ml⁻¹ after 12 days). Fungal spores, immobilized onto-into loofah sponge, in a bioreactor, using MGPB-citrate as feed stock, resulted in productivity of 23.04 mg compactin (L⁻¹ h⁻¹) during 50 days operation at 0.45 h⁻¹ dilution rate. Compactin synthesis in the bioreactor was also affected by culture age, substrate, incubation and dilution rates. Scanning electron micrographs of the loofah sponge, prior to, during and post-spores immobilization showed that loofah channels served well for fungal support in the bioreactor. Received 6 October 1997/ Accepted in revised form 2 September 1998