Grazing by the Antarctic sea-ice ciliate Pseudocohnilembus

Potential uptake and clearance rates of fluorescent microspheres (FM) from 0.25 to 4.05 μm diameter were determined for the non-loricate ciliate Pseudocohnilembus sp. from Antarctic sea ice. The percentage of ciliate cells that ingested FM after 20 min incubation decreased with increasing particle diameter. Pseudocohnilembus sp. ingested FM between 0.25 and 4.05 μm in diameter. We offered FM at concentrations less than natural concentrations for plankton plus detrital material and obtained clearance rates less than those previously reported for bactivorous ciliates. Clearance rates were 3.6–5.4 nl cell⁻¹ h⁻¹ for FM 0.5 and 1 μm diameter, respectively, but decreased to 1.1 nl cell⁻¹ h⁻¹ for 1.97 μm diameter and 1.4 nl cell⁻¹ h⁻¹ for 4.05-μm-diameter FM. Clearance and uptake rates of FM 0.5 and 1 μm diameter indicate that Pseudocohnilembus sp. principally grazes on bacteria-sized particles. However, it can also ingest organisms as large as nanoplankton and may graze particles as small as femtoplankton and colloids. This suggests a feeding strategy that may suit the temporal and spatial changes in food availability in the sea-ice habitat. Accepted: 13 August 2000     

Production of polyhydroxybutyrate by Ralstonia eutropha from protein hydrolysates

Polyhydroxybutyrate (PHB) was produced by Ralstonia eutropha DSM 11348 (formerly Alicaligenes eutrophus) in media containing 20–30 g l⁻¹ casein peptone or casamino acids as sole sources of nitrogen. In fermentations using media based on casein peptone, permanent growth up to a cell dry mass of 65 g l⁻¹ was observed. PHB accumulated in cells up to 60%–80% of dry weight. The lowest yields were found in media without any trace elements or with casamino acids added only. The residual cell dry masses were limited to 10–15 g l⁻¹ and did not contain PHB. The highest productivity amounted to 1.2 g PHB l⁻¹ h⁻¹. The mean molecular mass of the biopolymer was determined as 750 kDa. The proportion of polyhydroxyvalerate was less than 0.2% in PHB. The bioprocess was scaled up to a 300-l plant. During a fermentation time of 39 h the cells accumulated PHB to 78% w/w. The productivity was 0.98 g PHB l⁻¹ h¹. Received: 8 July 1998 / Accepted: 26 August 1998     

Degradation of naphthalene by cells of Pseudomonas sp. strain NGK 1 immobilized in alginate, agar and polyacrylamide

A Pseudomonas sp. strain NGK 1 (NCIM 5120) was immobilized in various matrices, namely, alginate, agar (1.8 × 10¹¹ cfu g⁻¹ beads) and polyacrylamide (1.6 × 10¹¹ cfu g⁻¹ beads). The degradation of naphthalene was studied, by freely suspended cells (4 × 10¹⁰ cfu ml⁻¹) and immobilized cells in batches, with shaken culture and continuous degradation in a packed-bed reactor. Free cells brought about the complete degradation of 25 mmol naphthalene after 3 days of incubation, whereas, a maximum of 30 mmol naphthalene was degraded by the bacteria after 3–4 days of incubation with 50 mmol and 75 mmol naphthalene, and no further degradation was observed even after 15 days of incubation. Alginate-entrapped cells had degraded 25 mmol naphthalene after 3.5 days of incubation, whereas agar- and polyacrylamide-entrapped cells took 2.5 days; 50 mmol naphthalene was completely degraded by the immobilized cells after 6–7 days of incubation. Maximum amounts of 55 mmol, 70 mmol and 67 mmol naphthalene were degraded, from an initial 75 mmol naphthalene, by the alginate-, agar- and polyacrylamide-entrapped cells after 15 days of incubation. When the cell concentrations were doubled, 25 mmol and 50 mmol naphthalene were degraded after 2 and 5.5 days of incubation by the immobilized cells. Complete degradation of 75 mmol naphthalene occurred after 10 days incubation with agar- and polyacrylamide-entrapped␣cells, whereas only 60 mmol naphthalene was degraded by alginate-entrapped cells after 15 days of␣incubation. Further, with 25 mmol naphthalene, alginate-, agar- and polyacrylamide-entrapped cells (1.8 × 10¹¹ cfu g⁻¹ beads) could be reused 18, 12 and 23 times respectively. During continuous degradation in a packed-bed reactor, 80 mmol naphthalene 100 ml⁻¹ h⁻¹ was degraded by alginate- and polyacrylamide-entrapped cells whereas 80 mmol naphthalene 125 ml⁻¹␣h⁻¹ was degraded by agar-entrapped cells. Received: 21 October 1997 / Received revision: 15 January 1998 / Accepted: 18 January 1998     

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     

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     

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     

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     

Energetic cost of hovering flight in a nectar-feeding bat measured with fast-response respirometry

Hover-feeding glossophagine bats provide, in addition to the hummingbirds, a second vertebrate model for the analysis of hovering flight based on metabolic measurement and aerodynamic theory. In this study, the power input of hovering Glossophaga soricina bats (11.9 g) was measured by standard respirometry and fast-response (<0.2 s) oxygen analysis. Bats needed 5–7 s after a rest-to-flight transition to return to a respiratory steady state. Therefore, only hovering events preceeded by a 7-s flight interval were evaluated. V˙_O2 during hovering fluctuated with a frequency of 3–5 Hz, which corresponded in frequency to the licking movement of the tongue. During hovering, bats often may have hypoventilated as indicated by reduced V˙_O2 and a respiratory exchange ratio (RER) well below the steady-state value of 1. Steady-state oxygen consumption (and derived power input) during hovering was estimated to be 27 (25–29) ml O₂ g⁻¹ h⁻¹ (158 W kg⁻¹ or 1.88 W) in the 11.9-g bats as indicated by three independent findings: (1) V˙_O2 was 26 ml O₂ g⁻¹ h⁻¹ after 6.5 s of hovering, (2) the mean RER during single hovering events was at its steady-state level of 1 only at oxygen uptake rates of 25–29 ml g⁻¹ h⁻¹, and (3) when the oxygen potentially released from estimated oxygen stores was added to the measured oxygen uptake, the upper limit for oxygen consumption during hovering was found to be 29 ml O₂ g⁻¹ h⁻¹. Hovering power input was about 1.2 times the value of minimum flight power input (Winter and von Helversen 1998) and thus well below the 1.7–2.6 difference in power output postulated by aerodynamic theory (Norberg et al. 1993). Mass specific power input was 40% less than in hummingbirds. Thus, within the possible modes of hovering flight, Glossophaga bats seem to operate at the high-efficiency end of the spectrum. Accepted: 28 April 1998     

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     

Production of high-density Chlorella culture grown in fermenters

The freshwater microalga Chlorella vulgaris was grown heterotrophically in fed-batch 50–600-L fermenters at 36°C, on aerated and mixed nutrient solution with urea as a nitrogen and glucose as a carbon and energy source. Cell density increased from the initial value 6.25 to 117.18 g DW L⁻¹ in 32 h in the fermenter 50 L at a mean growth rate 3.52 g DW L⁻¹ h⁻¹. The DW increase in the fermenter 200 L was from 7.25 to 94.82 g DW L⁻¹ in 26.5 h at a mean growth rate 3.37 g DW L⁻¹ h⁻¹. Mean specific growth rate μ was about 0.1 h⁻¹ in the both fermenters, if nutrients and oxygen were adequately supplied. The DW increase in the fermenter 600 L was from 0.8 to 81.6 g DW L⁻¹ in 66.5 h at a mean growth rate 1.22 g DW L⁻¹ h⁻¹ and μ = 0.07 h⁻¹. A limitation of the cell growth rate in 600 L fermenter caused by a low dissolved oxygen concentration above cell densities higher than 10 g DW L⁻¹) occurred. Specific growth rate decreased approximately linearly with increasing glucose concentration (25–80 g glucose L⁻¹) at the beginning of cultivation and decreased with the time of cultivation. The cell yield was 0.55–0.69 g DW (g glucose)⁻¹. The content of proteins, β-carotene, and chlorophylls in the cells steadily increased and starch content decreased, by keeping aerated and mixed culture another 12 h in fermenter after the cell growth was stopped due to glucose deficiency.     

The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol

A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam (PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR), packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation rate of phenol (q _s ^max) decreased in the order: PBRC (598 mg l⁻¹h⁻¹) > PBR (PU, 471 mg l⁻¹h⁻¹) > PBR (SG, 394 mg l⁻¹h⁻¹) > FBR (PU, 161 mg l⁻¹h⁻¹) > FBR (SG, 91 mg l⁻¹ h⁻¹). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100–200 μm thick layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized in colloidal SiO₂ enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic packing. Received: 2 December 1999 / Revision received: 2 February 2000 / Accepted: 4 February 2000     

Salt gland blood flow in the hatchling green turtle, Chelonia mydas

Microsphere and morphometric techniques were used to investigate any circulatory changes that accompany secretion by the salt glands of hatchling Chelonia mydas. Salt glands were activated by a salt load of 27.0 mmol NaCl kg body mass (BM)⁻¹, resulting in a mean sodium secretion rate of 4.14 ± 0.11 mmol Na kg BM⁻¹ h⁻¹ for a single gland. Microsphere entrapment was approximately 160–180 times greater in the active salt gland than the inactive gland, inferring a similar change in blood flow through salt gland capillaries. The concentration of microspheres trapped in the salt gland was significantly correlated with the rate of tear production (ml kg BM⁻¹ h⁻¹) and the total rate of sodium secretion (mmol Na kg BM⁻¹ h⁻¹) but not with tear sodium concentration (mmol Na l⁻¹). Adrenaline (500 μg kg BM⁻¹) inhibited tear production within 2 min and reduced microsphere entrapment by approximately 95% compared with active glands. The volume of filled blood vessels increased from 0.03 ± 0.01% of secretory lobe volume in inactive salt gland sections to 0.70 ± 0.11% in active gland sections. The results demonstrate that capillary blood flow in the salt gland of C. mydas can regulate the activity of the gland as a whole. Accepted: 12 July 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     

Glucoamylase production in batch, chemostat and fed-batch cultivations by an industrial strain of Aspergillus niger

The Aspergillus niger strain BO-1 was grown in batch, continuous (chemostat) and fed-batch cultivations in order to study the production of the extracellular enzyme glucoamylase under different growth conditions. In the pH range 2.5–6.0, the specific glucoamylase productivity and the specific growth rate of the fungus were independent of pH when grown in batch cultivations. The specific glucoamylase producivity increased linearly with the specific growth rate in the range 0–0.1 h⁻¹ and was constant in the range 0.1–0.2 h⁻¹. Maltose and maltodextrin were non-inducing carbon sources compared to glucose, and the maximum specific growth rate was 0.19 ± 0.02 h⁻¹ irrespective of whether glucose or maltose was the carbon source. In fed-batch cultivations, glucoamylase titres of up to 6.5 g l⁻¹ were obtained even though the strain contained only one copy of the glaA gene. Received: 5 May 1999 / Received revision: 7 September 1999 / Accepted: 17 September 1999     

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     

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     

Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae: Glossophaginae) and its scaling in moths, birds and bats

Three groups of specialist nectar-feeders covering a continuous size range from insects, birds and bats have evolved the ability for hovering flight. Among birds and bats these groups generally comprise small species, suggesting a relationship between hovering ability and size. In this study we established the scaling relationship of hovering power with body mass for nectar-feeding glossophagine bats (Phyllostomidae). Employing both standard and fast-response respirometry, we determined rates of gas exchange in Hylonycteris underwoodi (7 g) and Choeronycteris mexicana (13–18 g) during hover-feeding flights at an artificial flower that served as a respirometric mask to estimate metabolic power input. The O₂ uptake rate (V˙ _o2) in ml g⁻¹ h⁻¹ (and derived power input) was 27.3 (1.12 W or 160 W kg⁻¹) in 7-g Hylonycteris and 27.3 (2.63 W or 160 W kg⁻¹) in 16.5-g Choeronycteris and thus consistent with measurements in 11.9-g Glossophagasoricina (158 W kg⁻¹, Winter 1998). V˙ _o2 at the onset of hovering was also used to estimate power during forward flight, because after a transition from level forward to hovering flight gas exchange rates initially still reflect forward flight rates. V˙ _o2 during short hovering events (<1.5 s) was 19.0 ml g⁻¹ h⁻¹ (1.8 W) in 16-g Choeronycteris, which was not significantly different from a previous, indirect estimate of the cost of level forward flight (2.1 W, Winter and von Helversen 1998). Our estimates suggest that power input during hovering flight P _h (W) increased with body mass M (kg) within 13–18-g Choeronycteris (n = 4) as P _h  = 3544 (±2057 SE) M ^{1.76 (±0.21 SE)} and between different glossophagine bat species (n = 3) as P _h  = 128 (±2.4 SE) M ^{0.95 (±0.034 SE)}. The slopes of three scaling functions for flight power (hovering, level forward flight at intermediate speed and submaximal flight power) indicate that: 1. The relationship between flight power to flight speed may change with body mass in the 6–30-g bats from a J- towards a U-shaped curve. 2. A metabolic constraint (hovering flight power equal maximal flight power) may influence the upper size limit of 30–35 g for this group of flower specialists. Mass-specific power input (W kg⁻¹) during hovering flight appeared constant with regard to body size (for the mass ranges considered), but differed significantly (P < 0.001) between groups. Group means were 393 W kg⁻¹ (sphingid moths), 261 W kg⁻¹ (hummingbirds) and 159 W kg⁻¹ (glossophagine bats). Thus, glossophagine bats expend the least metabolic power per unit of body mass supported during hovering flight. At a metabolic power input of 1.1 W a glossophagine bat can generate the lift forces necessary for balancing 7 g against gravitation, whereas a hummingbird can support 4 g and a sphingid moth only 3 g of body mass with the same amount of metabolic energy. These differences in power input were not fully explained by differences in induced power output estimated from Rankine-Froude momentum-jet theory. Accepted: 10 November 1998     

Mineralization of pentachlorophenol in a contaminated soil by Pseudomonas sp UG30 cells encapsulated in κ-carrageenan

A fermentation process in Escherichia coli for production of supercoiled plasmid DNA for use as a DNA vaccine was developed using an automated feed-back control nutrient feeding strategy based on dissolved oxygen (DO) and pH. The process was further automated through a computer-aided data processing system to regulate the cell growth rate by controlling interactively both the nutrient feed rate and agitation speed based on DO. The process increased the total yield of the plasmid DNA by approximately 10-fold as compared to a manual fed-batch culture. The final cell yield from the automated process reached 60 g L⁻¹ of dry cell weight (OD₆₀₀ = 120) within 24 h. A plasmid DNA yield of 100 mg L⁻¹ (1.7 mg g⁻¹ cell weight) was achieved by using an alkaline cell lysis method. Plasmid yield was confirmed using High Performance Liquid Chromatography (HPLC) analysis. Because cells had been grown under carbon-limiting conditions in the automated process, acetic acid production was minimal (below 0.01 g L⁻¹) throughout the fed-batch stage. In contrast, in the manual process, an acid accumulation rate as high as 0.36 g L⁻¹ was observed, presumably due to the high nutrient feed rates used to maintain a maximum growth rate. The manual fed-batch process produced a low cell density averaging 10–12 g L⁻¹ (OD₆₀₀ = 25–30) and plasmid yields of 5–8 mg L⁻¹ (approximately 0.7 mg g⁻¹ cells). The improved plasmid DNA yields in the DO- and pH-based feed-back controlled process were assumed to be a result of a combination of increased cell density, reduced growth rate (μ) from 0.69 h⁻¹ to 0.13 h⁻¹ and the carbon/nitrogen limitation in the fed-batch stage. The DO- and pH-based feed-back control, fed-batch process has proven itself to be advantageous in regulating cell growth rate to achieve both high cell density and plasmid yield without having to use pure oxygen. The process was reproducible in triplicate fermentations at both 7-L and 80-L scales. Received 22 March 1996/ Accepted in revised form 20 September 1996     

Reduction of biomass in a bioscrubber for waste gas treatment by limited supply of phosphate and potassium ions

  Elimination of n-butanol from the gas phase was examined with a mixed culture in a compact bioscrubber. The extent of the cell concentration was limited by the supply of n-butanol, phosphate or potassium, and the growth rate was determined by the dilution rate. With n-butanol as the limiting substrate the cellular yield was 0.53 g dry cell weight/g n-butanol. Phosphate limitation decreased this yield to 0.34 g and potassium limitation to 0.31 g dry cell weight/g n-butanol at a dilution rate of 0.1/h. Under these conditions n-butanol was eliminated from the gas phase by 84%–100%. In the same order of limitations the specific degradation rate ranged from 0.19 g to 0.32 g n-butanol g dry cell weight⁻¹ h⁻¹. The fraction of n-butanol required to satisfy the needs for maintenance energy increased significantly depending on the limiting nutrient. Limitation by n-butanol, phosphate or potassium caused a maintenance requirement of 0.07, 0.16 and 0.34 g n-butanol g dry cell weight⁻¹ h⁻¹, thus showing a fivefold increase. This high demand for the carbon source demonstrated the feasibility of operating a bioscrubber under mineral limitation to reduce biomass formation significantly, and to maintain a high degree of substrate elimination from the gas phase. Received: 22 May 1996 / Received revision: 23 July 1996 / Accepted: 5 August 1996     

Fed-batch production of unsaturated medium-chain-length polyhydroxyalkanoates with controlled composition by <Emphasis Type="Italic">Pseudomonas putida</Emphasis> KT2440

Unsaturated medium-chain-length polyhydroxyalkanoates (MCL-PHA) were produced at a productivity of 0.63–1.09 g PHA l⁻¹ h⁻¹ with final PHA content ranging from 42.6 to 55.8% in single-stage, carbon-limited, fed-batch fermentations of Pseudomonas putida KT2440. A mixture of nonanoic acid (NA) and 10-undecenoic acid (UDA⁼) was fed exponentially to control growth rate. Varying the specific growth rate (0.14 h⁻¹ vs. 0.23 h⁻¹) at similar substrate feed ratios (NA:UDA⁼ = 5:1) had little effect on the final PHA content and relative composition. However, decreasing the NA:UDA⁼ ratio decreased the final amount of PHA produced from 56% with NA:UDA⁼ = 5.07:1 to only 42% at NA:UDA⁼ = 2.47:1. The molar fraction of all 3-hydroxyalkanoate monomers in the PHA product was relatively constant throughout each fermentation, indicating that the final product was homogeneous rather than a mixture of different copolymers. A linear relationship between unsaturation of the PHA produced and unsaturation of the carbon feed was found, which demonstrates the feasibility of producing unsaturated MCL-PHAs with controlled polymeric composition in a fed-batch process.