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     

Liquid media development for Heterorhabditis bacteriophora : lipid source and concentration

Lipids are important entomopathogenic nematode nutritional components because they are energy reserves and serve as indicators of nematode quality. The composition and concentration of the media lipid component determine bacterial and nematode yields. Heterorhabditis bacteriophora and its symbiont, Photorhabdus luminescens, were cultured in media containing various lipid sources. As lipid concentration increased from 2.5% to 8.0% (w/v), the final yield and productivity [calculated from the number of infective juveniles (IJ)] increased significantly from 2.1 × 10⁵IJ ml⁻¹ to 2.8 × 10⁵IJ ml⁻¹ (P < 0.05) and from 8.9 × 10⁵IJ l⁻¹ day⁻¹ to 11.8 × 10⁵ IJ l⁻¹day⁻¹ (P < 0.05), respectively. The nematode yield coefficient (IJ per gram of media), however, decreased from 2.8 × 10⁶ to 2.2 × 10⁶ (P < 0.05), while recovery increased from 45.3% to 58.0% (P < 0.05). Bacterial cell mass remained constant at 4.6 mg ml⁻¹ with changing lipid content (P > 0.05). The largest nematode yield (2.8 × 10⁵IJ ml⁻¹) was achieved within 8 days, using a medium containing an 8% (w/v) olive and canola oil (50:50 w/v) combination. Moreover, developmental synchrony was achieved in this medium with 96% infective juveniles. In short, lipid sources rich in mono-unsaturated fatty acids and poor in saturated fatty acids produced optimal nematode growth. Received: 1 May 2000 / Received revision: 17 July 2000 / Accepted: 27 July 2000     

Enumeration of bacteria from a Trichodesmium spp. bloom of the Eastern Arabian Sea: elucidation of their possible role in biogeochemistry

The carbon-flux via algal bloom events involves bacteria as an important mediator. The present study, carried out during the spring inter-monsoon month of April 2008 onboard CRV Sagar Manjusha-06 in the Eastern Arabian Sea, addresses the bloom-specific flow of carbon to bacteria via chromophoric dissolved organic matter (CDOM). Eleven stations monitored were located in the coastal, shelf and open-ocean areas off Ratnagiri (16°59′N, 73°17′E), Goa (15°30′N, 73°48′E) and Bhatkal (13°58′N, 74°33′E) coasts. Visible bloom of “saw-dust” color in the Ratnagiri shelf were microscopically examined and the presence of cyanobacteria Trichodesmium erythraeum and T. thieabautii with cell concentrations as high as 3.05 × 10⁶ trichomes L⁻¹ was recorded. Total bacterial counts (TBC) varied between 94.09 × 10⁸ cells L⁻¹ in the bloom to 1.34 × 10⁸ cells L⁻¹ in the non-bloom area. Chromophoric dissolved organic matter (CDOM) concentrations averaged 2.27 ± 3.02 m⁻¹ (absorption coefficient 325 nm) in the bloom to 0.28 ± 0.07 m⁻¹ in the non-bloom waters respectively. CDOM composition varied from a higher molecular size with lower aromaticity in the bloom to lower molecular size and increased aromaticity in the non-bloom areas respectively. Strong positive relationship of TBC with Chlorophyll a (R ² = 0.65, p < 0.01) and CDOM concentrations (R ² = 0.8373, p = 0.01) in the bloom area indicated hydrolysis and/or uptake of CDOM by bacteria. Absorption by mycosporine-like amino acid palythene (λ _max = 360 nm) was recorded in the filtrate of bloom. Morphotypes of Trichodesmium-associated bacteria revealed a higher frequency of Gram-positive rods. The role of bacteria in relation to changing CDOM nature and as a factor in affecting oxygen content of the water column is discussed in context of the Arabian Sea.     

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     

Differences among plant species in cuticular permeabilities and solute mobilities are not caused by differential size selectivities

Solute mobilities in cuticular membranes of six species (Hedera helix, Malus domestica, Populus alba, Pyrus communis, Stephanotis floribunda, Strophantus gratus) were measured using plant hormones, growth regulators and other organic model compounds varying in molar volumes from 99 to 349 mL · mol⁻¹ The dependence of mobilities (k*) on molar volume (V _x ) was exponential and could be described with equations of the type log k*=log k*⁰−^′ V _x . The y-intercepts (log k*⁰) represent mobilities of a hypothetical solute of zero molar volume. The parameter β′ is a measure of size selectivity of cuticular membranes and no differences among the six species were observed. At 25 °C the average β′ was 0.0095 mol · mL⁻¹. Solute mobility decreased by about a factor of 8.9 when molar volume increased by 100 mL · mol⁻¹ and the mobility of a compound with V _x  = 100 mL · mol⁻¹ was about 700-fold higher than the mobility of a compound with V _x  = 400 mL · mol⁻¹. Size selectivity decreased with increasing temperatures and for Strophantusβ′-values of 1.6 × 10⁻² to 8.0 × 10^-4 mol · mL⁻¹ were obtained for 10 and 30 °C, respectively. The-intercepts (log k*⁰) differed among plant species by 3 orders of magnitude and since size selectivity was the same for all species, solute mobilities for solutes having zero molar volumes were the sole cause for differences among species in solute mobilities and permeabilities. We argue that these differences in k*⁰ are related to tortuosity of the diffusion path. These results were used to derive an equation which predicts rates of cuticular penetration on the basis of k*⁰, the average size selectivity of 9.5 × 10⁻³ mol · mL⁻¹ and the driving forces of penetration. Received: 25 November 1997 / Accepted: 9 March 1998     

Plasma arginine vasotocin and angiotensin II responses to body temperature elevation in the Pekin duck

The relationship between body temperature (T _b) and the plasma concentrations of arginine vasotocin (AVT) and angiotensin II (AII) was examined in conscious, adult Pekin ducks. Exposure of birds to an ambient temperature of 40 °C for 3 h increased T _b by about 1.5 °C and increased breathing rate five-fold. Plasma osmolality was elevated from the normothermic value of 294.9 ± 1.4 mosmol kg⁻¹ by about 8 mosmol kg⁻¹ Circulating AVT levels increased by about 2 pg ml⁻¹ from a basal concentration of 4.98 ± 0.15 pg ml⁻¹, a rise which could be accounted for by the change in osmotic status. Plasma AII concentrations were unchanged from the pre-heat exposure value of 31.8 ± 3.4 pg ml⁻¹. Time control birds, exposed only to an ambient temperature of 22 °C demonstrated no significant changes in any of the measured variables. The results suggest that an increased T _b has no direct effect on the circulating concentrations of AVT or AII in ducks. Accepted: 2 June 1997     

Biofilm formation on brass coupons exposed to a cooling system of an oil refinery

Brass coupons (70% Cu 30% Zn) were exposed to a cooling freshwater system of an oil refinery, in order to investigate susceptibility of the metal to biofilm formation. The coupons were fixed on bypasses at points which allowed the circulation of makeup, cooling and return water. The number of aerobic, anaerobic and sulfate-reducing bacteria was determined in both the planktonic and the sessile phases. Maximum bacterial concentrations were detected in the cooling water, corresponding to 2.1 ± 0.1 × 10⁶ CFU ml⁻¹ (planktonic phase) and 1.3 ± 0.2 × 10⁵ CFU cm⁻² (sessile phase) for aerobic bacteria and to 3.2 ± 0.3 × 10⁵ cells ml⁻¹ (planktonic phase) and 6.2 ± 0.7 × 10⁵ cells cm⁻² (sessile phase) for anaerobic bacteria. Sulfate-reducing bacteria (SRB) were observed only in the planktonic phase, being found in greater numbers in the return water. Scanning electron microscopy (SEM) analysis indicated that biofilm formation occurred at the three monitored sites and showed a diversity in cell morphology. Nonetheless, no evidence of corrosion was observed on the brass coupons during the experimental period. Received 22 May 1997/ Accepted in revised form 19 September 1997     

Studies on water transport through the sweet cherry fruit surface: characterizing conductance of the cuticular membrane using pericarp segments

Water conductance of the cuticular membrane (CM) of mature sweet cherry fruit (Prunus avium L. cv. Sam) was investigated by monitoring water loss from segments of the outer pericarp excised from the cheek of the fruit. Segments consisted of epidermis, hypodermis and several cell layers of the mesocarp. Segments were mounted in stainless-steel diffusion cells with the mesocarp surface in contact with water, while the outer cuticular surface was exposed to dry silica (22 ± 1 °C). Conductance was calculated by dividing the amount of water transpired per unit area and time by the difference in water vapour concentration across the segment. Conductance values had a log normal distribution with a median of 1.15 × 10⁻⁴ m s⁻¹ (n=357). Transpiration increased linearly with time. Conductance remained constant and was not affected by metabolic inhibitors (1 mM NaN₃ or 0.1 mM carbonylcyanide m-chlorophenylhydrazone) or thickness of segments (range 0.8–2.8 mm). Storing fruit (up to 42 d, 1 °C) used as a source of segments had no consistent effect on conductance. Conductance of the CM increased from cheek (1.16 ± 0.10 × 10⁻⁴ m s⁻¹) to ventral suture (1.32 ± 0.07 × 10⁻⁴ m s⁻¹) and to stylar end (2.53 ± 0.17 × 10⁻⁴ m s⁻¹). There was a positive relationship (r²=0.066**; n=108) between conductance and stomatal density. From this relationship the cuticular conductance of a hypothetical astomatous CM was estimated to be 0.97 ± 0.09 × 10⁻⁴ m s⁻¹. Removal of epicuticular wax by stripping with cellulose acetate or extracting epicuticular plus cuticular wax by dipping in CHCl₃/methanol increased conductance 3.6- and 48.6-fold, respectively. Water fluxes increased with increasing temperature (range 10–39 °C) and energies of activation, calculated for the temperature range from 10 to 30 °C, were 64.8 ± 5.8 and 22.2 ± 5.0 kJ mol⁻¹ for flux and vapour-concentration-based conductance, respectively. Received: 23 March 2000 / Accepted: 28 July 2000     

An alginate-layer technique for culture of Brassica oleracea L. protoplasts

Ten accessions belonging to the Brassica oleracea subspecies alba and rubra, and to B. oleracea var. sabauda were used in this study. Protoplasts were isolated from leaves and hypocotyls of in vitro grown plants. The influence of selected factors on the yield, viability, and mitotic activity of protoplasts immobilized in calcium alginate layers was investigated. The efficiency of protoplast isolation from hypocotyls was lower (0.7 ± 0.1 × 10⁶ ml⁻¹) than for protoplasts isolated from leaf mesophyll tissue (2 ± 0.1 × 10⁶ ml⁻¹). High (70–90%) viabilities of immobilized protoplasts were recorded, independent of the explant sources. The highest proportion of protoplasts undergoing divisions was noted for cv. Reball F1, both from mesophyll (29.8 ± 2.2%) and hypocotyl (17.5 ± 0.3%) tissues. Developed colonies of callus tissue were subjected to regeneration and as a result plants from six accessions were obtained.     

Production of recombinant herpes simplex virus protease in 10-L stirred vessels using a baculovirus–insect cell expression system

A gene expression system using recombinant Autographa californica nuclear polyhedrosis virus (baculovirus) and Sf-9 cells has been scaled up to the 10-L tank level and shown to be capable of producing herpes simplex virus (HSV) protease in serum-free media. High densities of Spodoptera frugiperda (Sf-9) cells were achieved by modifying two 10-L Biolafitte fermenters specifically for insect cell growth. The existing Rushton impellers were replaced by marine impellers to reduce shear and the aeration system was modified to allow external addition of air/O₂ mixtures at low flow rates through either the sparge line or into the head space of the fermenter. To inoculate the tanks, Sf-9 cells were adapted to grow to high cell densities (6–10 × 10⁶ cells ml⁻¹) in shake flasks in serum-free media. With these procedures, cell densities of 5 × 10⁶ cells ml⁻¹ were routinely achieved in the 10-L tanks. These cells were readily infected with recombinant baculovirus expressing the 247-amino acid catalytic domain of the HSV-1 strain 17 protease UL26 gene as a glutathione-S-transferase (GST) fusion protein (GST-247). Three days after infection at a multiplicity of infection (MOI) of 3 pfu cell⁻¹, the GST-247 fusion protein was purified from a cytoplasmic lysate by Glutathione Sepharose 4-B affinity chromatography with reproducible yields of 11–38 mg L⁻¹ of recombinant protein and ≥ 90% purity. Maximum production of this protein was observed at a cell density of 5.0 × 10⁶ cells ml⁻¹. Received 09 December 1996/ Accepted in revised form 13 April 1997     

Use of clove oil to anaesthetize freshwater amphipods

The use of clove oil as a potential anaesthetic for freshwater amphipods was examined at 20 °C. Individuals of Gammarus minus, a common species in southern Illinois, USA, spanning the entire body size range (4.3–14.3 mm), were used to test four anaesthetic concentrations varying from 1.48 × 10⁻⁴ ml ml⁻¹ to 5.9 × 10⁻⁴ ml ml⁻¹. Small-bodied individuals (mean size = 5.4 mm ± 0.27SE) were used to test additional concentrations, up to 14.7 × 10⁻⁴ ml ml⁻¹, a 10-fold span, to identify potential lethal concentrations. At the lowest concentration, time to anaesthesia and recovery was constant at all body sizes. For the three next higher concentrations, time to anaesthesia decreased with increasing concentration while recovery time increased. Activity of amphipods was not affected by the ethanol carrier. In addition, activity did not differ between amphipods that had recovered from anaesthesia and unexposed amphipods. At clove oil concentrations of 8.84 × 10⁻⁴ ml ml⁻¹ and 14.7 × 10⁻⁴ ml ml⁻¹, mortality was 7 and 40%, respectively, indicating, that 5.9 × 10⁻⁴ ml ml⁻¹ was a safe working concentration. No mortality was observed with Gammarus acherondytes, a federally endangered cave amphipod on which the protocol with 80 μl of stock was used in the field. The method enabled us to obtain information on the endangered amphipod which normally would have required the sacrifice of individuals. Thus, research can continue on species for which population numbers are low and for which basic information is needed to formulate meaningful recovery plans.     

Annual and interannual variability in phytoplankton at a permanent station off Kerguelen Islands, Southern Ocean

From November 1992 to February 1995 a quantitative and qualitative phytoplankton study was conducted at a permanent station (Kerfix) southwest off the Kerguelen Islands, in the vicinity of the Polar Front (50°40′S–68°25′E). Phytoplankton populations are low in this area both during summers and winters. They consist, in order of decreasing cell abundance, of pico- and nanoflagellates (1.5–20 μm), coccolithophorids (<10 μm), diatoms (5–80 μm) and dinoflagellates (6–60 μm). Flagellates form the dominant group throughout the year and attain the highest summer average of 3.0 × 10⁵ cells l⁻¹. Next in abundance year-round are coccolithophorids with the dominant Emiliania huxleyi (highest summer 1992 average 1.9 × 10⁵ cells l⁻¹), diatoms (summer 1992 average 1.0 × 10⁵ cells l⁻¹) and dinoflagellates (average 3.8 × 10⁴ cells l⁻¹). Winter mean numbers of flagellates and picoplankton do not exceed 8.4 × 10⁴ cells l⁻¹; those of the three remaining algal groups together attain 2 × 10⁴ cells l⁻¹. Summer peaks of diatoms and dinoflagellates are mainly due to the larger size species (>20 μm). The latter group contributes most to the total cell carbon biomass throughout the year. Dominant diatoms during summer seasons include: Fragilariopsis kerguelensis, Thalassionema nitzschioides, Chaetoceros dichaeta, C. atlanticus, Pseudonitzschia heimii, and P. barkleyi/lineola. This diatom dominance structure changes from summer to summer with only F. kerguelensis and T. nitzschioides retaining their first and second positions. Any one of the co-dominant species might be absent during some summer period. The variable diatom community structure may be due to southward meandering of the Polar Front bringing “warmer” species from the north, and to the mixing of the water masses in this area. The entire community structure characterized both during summer and winters by the dominance of flagellates can be related to deep mixing (ca. 40–200 m) of the water column as the probable controlling factor. Received: 13 November 1997 / Accepted: 11 May 1998     

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     

Role of cyclic nucleotides in pigment translocation within the freshwater shrimp, Macrobrachium potiuna, erythrophore

The participation of cyclic nucleotide-dependent intracellular signalling pathways in the pigment translocation induced by pigment-dispersing hormone (α -PDH) or pigment-concentrating hormone (PCH) was investigated in the erythrophores of the freshwater shrimp, Macrobrachium potiuna. Cholera toxin, forskolin and dibutyryl cyclic adenosine 3′5′ monophosphate (dbcAMP) were able to induce pigment dispersion with effective agonist concentrations for half maximal response (EC₅₀s) of 2.8 · 10⁻¹¹ mol · l⁻¹, 7.0 · 10⁻⁷ mol · l⁻¹ and 3.3 · 10⁻⁷ mol · l⁻¹, respectively. KT5720 (10⁻⁷ mol · l⁻¹ and 10⁻⁶ mol · l⁻¹) significantly shifted the dose response curve to α -PDH to the right. Dibutyryl cyclic guanosine 3′5′ monophosphate (dbcGMP) was ineffective in inducing either pigment aggregation or dispersion. 2′5′ dideoxyadenosine (DDA) and SQ22,536 essentially elicit a pigment-aggregating response in a dose-dependent manner. These effects were not due to the activation of purinergic receptors, since concentrations up to 10⁻⁴ mol · l⁻¹ of adenosine and adenosine triphosphate (ATP), and up to 10⁻³ mol · l⁻¹ of uracil triphosphate (UTP) did not elicit pigment aggregation. In order to verify if PCH decreased cyclic adenosine 3′5′ monophosphate (cAMP) levels, cumulative dose-response curves to PCH in the absence and presence of pertussis toxin and 8-MOM-IBMX were determined. However, neither drug significantly affected PCH activity. The levels of cAMP in the integument cells of M. potiuna were significantly increased (P < 0.05) by α -PDH (10⁻⁷ mol · l⁻¹) and forskolin (10⁻⁶ mol · l⁻¹), but were not affected by PCH (10⁻⁷ or 10⁻¹⁰ mol · l⁻¹). In conclusion, α -PDH seems to elicit pigment dispersion through the activation of a Gs-protein coupled receptor resulting in cAMP increase and cAMP-dependent protein kinase (PKA) activation. Furthermore, although a decrease in cAMP was assumed to be responsible in turn for the action of PCH, such a decrease could not be directly demonstrated. Accepted: 11 August 1998     

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     

Modeling growth for predicting the contamination level of guava nectar by Candida pelliculosa under different conditions of pH and storage temperature

The combined effects of temperature (2–46°C) and pH (1.55–6.25) on the growth of Candida pelliculosa isolated from guava nectar produced in Cameroon were studied using a turbidity method, ie measurement of optical density at 630 nm. A quadratic polynomial model was constructed to predict the effects and interactions of these two environmental conditions on the maximal optical density obtained (r ² = 0.97). The relation between optical density and population density of C. pelliculosa (CFU ml⁻¹) was also established using an exponential regression (r ² = 0.99). According to the model, maximal growth conditions were 37°C and pH 6.25 for obtaining the maximal optical density of 1.25 corresponding to about 60 × 10⁶ CFU ml⁻¹. A good agreement of the model was found between the predicted values and the observed values of maximal optical density. The model was validated by the experimental values of maximal optical density obtained in the growth of C. pelliculosa in commercial guava nectar (pH 3.15). Received 01 December 1995/ Accepted in revised form 30 August 1996     

Seasonal changes of Antarctic marine bacterioplankton and sea ice bacterial assemblages

The distributions of bacterial populations in sea ice and underlying seawater were investigated on the continental shelf of the “Terre Adélie” area. A reference station was sampled weekly from January 1991 to January 1992. In winter, the survey included a minimum of six sampling layers: surface and bottom ice, brine, seawater from the interface, and at 0.5 and 2 m depth. In seawater, the total bacterial abundance ranged from 0.5 × 10⁵ cells ml⁻¹ in July to 6.0 × 10⁵ cells ml⁻¹ after ice break. Values reaching 2.5 × 10⁶ cells ml⁻¹ were recorded in the overlying ice cover. Mean cell volumes were twice as high in brine as in seawater. The saprophytic bacterial abundance ranged from 5.0 × 10⁴ CFU (colony-forming units) ml⁻¹ in some winter interface samples to less than 1.0 × 10³ CFU ml⁻¹ in most of the summer seawater samples. In sea ice a clear decreasing gradient for most of the studied bacterial parameters from the surface layers towards the bottom layer was found. The ice cover had a discernible impact on underlying seawater, but its influence was restricted to a limited interface layer.     

Antarctic sea ice viral dynamics over an annual cycle

Viral abundance, burst sizes, lytic production and temperate phage were investigated in land-fast ice at two sites in Prydz Bay Antarctica (68°S, 77°E) between April and November 2008. Both ice cores and brine were collected. There was no seasonal pattern in viral or bacterial numbers. Across the two sites virus abundances ranged between 0.5 × 10⁵ and 5.1 × 10⁵ viruses ml⁻¹ in melted ice cores and 0.6 × 10⁵–3.5 × 10⁵ viruses ml⁻¹ in brine, and bacterial abundances between 2.7 × 10⁴ and 17.3 × 10⁴ cells ml⁻¹ in melted ice cores and 3.9 × 10⁴–32.5 × 10⁴ cells ml⁻¹ in brine. Virus to bacterium ratios (VBR) showed a clear seasonal pattern in ice cores with lowest values in winter (range 1.2–20.8), while VBRs in brine were lower (0.2–4.9). Lytic viral production range from undetectable to 2.0 × 10⁴ viruses ml⁻¹ h⁻¹ in ice cores with maximum rates in September and November. In brine maximum, lytic viral production occurred in November (1.18 × 10⁴ viruses ml⁻¹ h⁻¹). Low burst sizes were typical (3.94–4.03 viruses per bacterium in ice cores and 3.16–4.0 viruses per bacterium in brine) with unusually high levels of visibly infected cells—range 40–50%. This long-term investigation revealed that viral activity was apparent within the sea ice throughout its annual cycle. The findings are discussed within the context of limited data available on viruses in sea ice.     

Determination of shelf life of <Emphasis Type="Italic">Spirulina platensis</Emphasis> (MI<Subscript>2</Subscript>) grown in the Philippines

Gamma linolenic acid (GLA) degradation in Spirulina followed first-order reaction kinetics. At an accelerated temperature range of 45 to 55°C, the degradation rate constants (k _r) of GLA obtained were 4.0 × 10⁻² to 8.8 × 10⁻² day⁻¹. The energy of activation (E _a) was 16.53 kcal mol⁻¹, and the Q₁₀ was 2.22. Based on 20% GLA degradation, the shelf life of sun-dried Spirulina at 30°C is 263 days or 8.6 months using the Arrhenius plot, and 258 days or 8.5 months using the Q ₁₀ approach. Presented at the 6th Meeting of the Asia Pacific Society of Applied Phycology, Manila, Philippines.     

Carob pulp as raw material for production of the biocontrol agent <Emphasis Type="Italic">P. agglomerans</Emphasis> PBC-1

Large-scale production has been the major obstacle to the success of many biopesticides. The spreading of microbial biocontrol agents against postharvest disease, as a safe and environmentally friendly alternative to synthetic fungicides, is quite dependent on their industrial mass production from low-cost raw materials. Considerable interest has been shown in using agricultural waste products and by-products from food industry as nitrogen and carbon sources. In this work, carob pulp aqueous extracts were used as carbon source in the production of the biocontrol agent Pantoea agglomerans PBC-1. Optimal sugar extraction was achieved at a solid/liquid ratio of 1:10 (w/v), at 25°C, for 1 h. Batch experiments were performed in shake flasks, at different concentrations and in stirred reactors at two initial inoculums concentrations, 10⁶ and 10⁷ cfu ml⁻¹. The initial sugar concentration of 5 g l⁻¹ allowed rapid growth (0.16 h⁻¹) and high biomass productivity (0.28 g l⁻¹ h⁻¹) and was chosen as the value for use in stirred reactor experiments. After 22 and 32 h of fermentation the viable population reached was 3.2 × 10⁹ and 6.2 × 10⁹ cfu ml⁻¹ in the fermenter inoculated at 10⁶ cfu ml⁻¹ and 2.7 × 10⁹ and 6.7 × 10⁹ cfu ml⁻¹ in the bioreactor inoculated at 10⁷ cfu ml⁻¹. A 78% reduction of the pathogen incidence was achieved with PBC-1 at 1 × 10⁸ cfu ml⁻¹, grown in medium with carob extracts, on artificially wounded apples stored after 7 days at 25°C against P. expansum.