Mutation rate and pattern of microsatellites in common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.)

Microsatellites are popular molecular markers in genetic and evolutionary studies. Their mutational dynamics have been extensively studied in humans and fruit flies, but few data were available in fish. By genotyping 55 individuals of a F1 pedigree, we investigated the mutation rates and patterns of 49 microsatellites in one of the most important fresh water fish species, the common carp (Cyprinus carpio L.). The overall mutation rate of the 49 loci was 5.56×10⁻⁴/locus/generation (95% confidence interval 1.52×10⁻⁴ and 1.63×10⁻³). The change of allele size was between +2 to −5 repeat units, assuming that the mutation allele arose from the parental allele most similar in size to the mutant.     

Atopic dermatitis in West Highland white terriers is associated with a 1.3-Mb region on CFA 17

Canine atopic dermatitis (AD) is an allergic inflammatory skin disease that shares similarities with AD in humans. Canine AD is likely to be an inherited disease in dogs and is common in West Highland white terriers (WHWTs). We performed a genome-wide association study using the Affymetrix Canine SNP V2 array consisting of over 42,800 single nucleotide polymorphisms, on 35 atopic and 25 non-atopic WHWTs. A gene-dropping simulation method, using SIB-PAIR, identified a projected 1.3 Mb area of association (genome-wide P = 6 × 10⁻⁵ to P = 7 × 10⁻⁴) on CFA 17. Nineteen genes on CFA 17, including 1 potential candidate gene (PTPN22), were located less than 0.5 Mb from the interval of association identified on the genome-wide association analysis. Four haplotypes within this locus were differently distributed between cases and controls in this population of dogs. These findings suggest that a major locus for canine AD in WHWTs may be located on, or in close proximity to an area on CFA 17.     

RETRACTED ARTICLE: Archaeal <Emphasis Type="Italic">amoA</Emphasis> Genes Outnumber Bacterial <Emphasis Type="Italic">amoA</Emphasis> Genes in Municipal Wastewater Treatment Plants in Bangkok

The contribution of ammonia-oxidizing archaea (AOA) to nitrogen removal in wastewater treatment plants (WWTPs) remains unknown. This study investigated the abundance of archaeal (AOA) and bacterial (ammonia-oxidizing bacteria (AOB)) amoA genes in eight of Bangkok’s municipal WWTPs. AOA amoA genes (3.28 × 10⁷ ± 1.74 × 10⁷–2.23 × 10¹¹ ± 1.92 × 10¹¹ copies l⁻¹ sludge) outnumbered AOB amoA genes in most of the WWTPs even though the plants’ treatment processes, influent and effluent characteristics, removal efficiencies, and operation varied. An estimation of the ammonia-oxidizing activity of AOA and AOB suggests that AOA involved in autotrophic ammonia oxidation in the WWTPs. Statistical analysis shows that the numbers of AOA amoA genes correlated negatively to the ammonium levels in effluent wastewater, while no correlation was found between the AOA amoA gene numbers and the oxygen concentrations in aeration tanks. An analysis of the AOB sequences shows that AOB found in the WWTPs limited to only two AOB clusters which exhibit high or moderate affinity to ammonia. In contrast to AOB, AOA sequences of various clusters were retrieved, and they were previously recovered from a variety of environments, such as thermal and marine environments.     

Genetic Variability of Thermal <Emphasis Type="Italic">Nymphaea</Emphasis> (Nymphaeaceae) Populations Based on ISSR Markers: Implications on Relationships,Hybridization, and Conservation

The globally widespread genus Nymphaea exhibits a wide range of morphological and taxonomical diversity. The intrusion of a cultivated variety by progressive propagation and its affect on aquatic habitat is demonstrated in this case study. We have studied the genetic diversity, population, and stand structure of the neophyte Nymphaea × ‘Panama Pacific’ as well as other species found in Lake Hévíz and dikes nearby using inter-simple sequence repeat (ISSR) markers. The ISSR assay revealed a low genetic variability for the small populations of Nymphaea caerulea, Nymphaea lotus var. thermalis, and a medium level for Nymphaea alba, Nymphaea rubra var. longiflora, and Nymphaea × ‘Panama Pacific’. The evolutionary genetic status of individuals found in the overlapping cultivation area of Nymphaea × ‘Panama Pacific’ and N. caerulea was affirmed to be of hybrid origin by reticulate network analysis and with morphological parameters. The Bayesian analysis of hybrid classes and the segregation of the ISSR markers also confirmed the hybrid origin of the individuals in question and revealed that they are falling into F2 or latter genotype frequency classes, indicating the viability and fertility of the hybrids. The set of analyzed species by phylogenetic network analysis of ISSR data has been divided into three major groups according to their evolutionary patterns (subg. Barachyceras, Lotos, and Nymphaea). Our results are in accordance with these three major subgenera within Nymphaea.     

Migratory history and habitat use by New Zealand freshwater eels <Emphasis Type="Italic">Anguilla dieffenbachii</Emphasis> and <Emphasis Type="Italic">A. australis</Emphasis>, as revealed by otolith microchemistry

 The migratory history of Anguilla dieffenbachii and A. australis, collected from a coastal lake of New Zealand, was examined using analysis of strontium (Sr) and calcium (Ca) concentrations. Line analysis of Sr : Ca ratios along the life history transect of each otolith showed a peak (Ca. 16–20 × 10⁻³) between the core and elver mark, which corresponded to the period of their leptocephalus and early glass eel stages in the ocean. The mean Sr : Ca ratios from the elver mark to the otolith edge indicated that eels had different migratory histories, which included freshwater residency in some eels (average Sr : Ca ratios, 1.7 × 10⁻³–2.4 × 10⁻³) but not in others (average Sr : Ca ratios, 3.1 × 10⁻³–6.5 × 10⁻³). These findings suggest that New Zealand freshwater eels have a flexible migration strategy and an ability to adapt to various habitats and salinities. Received: November 25, 2002 / Revised: January 17, 2003 / Accepted: January 17, 2003     

Diversity and quantity of ammonia-oxidizing Archaea and Bacteria in sediment of the Pearl River Estuary, China

The diversity and abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the sediment of the Pearl River Estuary were investigated by cloning and quantitative real-time polymerase chain reaction (qPCR). From one sediment sample S16, 36 AOA OTUs (3% cutoff) were obtained from three clone libraries constructed using three primer sets for amoA gene. Among the 36 OTUs, six were shared by all three clone libraries, two appeared in two clone libraries, and the other 28 were only recovered in one of the libraries. For AOB, only seven OTUs (based on 16S rRNA gene) and eight OTUs (based on amoA gene) were obtained, showing lower diversity than AOA. The qPCR results revealed that AOA amoA gene copy numbers ranged from 9.6 × 10⁶ to 5.1 × 10⁷ copies per gram of sediment and AOB amoA gene ranged from 9.5 × 10⁴ to 6.2 × 10⁵ copies per gram of sediment, indicating that the dominant ammonia-oxidizing microorganisms in the sediment of the Pearl River Estuary were AOA. The terminal restriction fragment length polymorphism results showed that the relative abundance of AOB species in the sediment samples of different salinity were significantly different, indicating that salinity might be a key factor shaping the AOB community composition.     

Seasonal Dynamics and Modeling of a <Emphasis Type="Italic">Vibrio</Emphasis> Community in Coastal Waters of the North Sea

Vibrio species are ubiquitously distributed in marine waters all over the world. High genome plasticity due to frequent mutation, recombination, and lateral gene transfer enables Vibrio to adapt rapidly to environmental changes. The genus Vibrio comprises several human pathogens, which commonly cause outbreaks of severe diarrhea in tropical regions. In recent years, pathogenic Vibrio emerged also in coastal European waters. Little is known about factors driving the proliferation of Vibrio spp. in temperate waters such as the North Sea. In this study a quantification of Vibrio in the North Sea and their response to biotic and abiotic parameters were assessed. Between January and December 2009, Vibrio at Helgoland Roads (North Sea, Germany) were quantified using fluorescence in situ hybridization. Vibrio numbers up to 3.4 × 10⁴ cells × mL⁻¹ (2.2% of total microbial counts) were determined in summer, but their abundance was significantly lower in winter (5 × 10² cells × mL⁻¹). Correlations between Vibrio and nutrients (SiO₂, PO₄ ³⁻, DIN), Secchi depth, temperature, salinity, and chlorophyll a were calculated using Spearman rank analysis. Multiple stepwise regression analysis was carried out to analyze the additive influence of multiple factors on Vibrio. Based on these calculations, we found that high water temperature and low salinity best explained the increase of Vibrio cell numbers. Other environmental parameters, especially nutrients and chlorophyll a, also had an influence. All variables were shown to be subject to the overall seasonal dynamics at Helgoland Roads. Multiple regression models could represent an efficient and reliable tool to predict Vibrio abundances in response to the climate change in European waters.     

Addition of allochthonous fungi to a historically contaminated soil affects both remediation efficiency and bacterial diversity

Botryosphaeria rhodina DABAC P82 and Pleurotus pulmonarius CBS 664.97 were tested for their ability to grow and to degrade aromatic hydrocarbons in an aged contaminated soil. To evaluate the impact of indigenous microflora on the overall process, incubations were performed on both fumigated and nonfumigated soils. Fungal colonization by B. rhodina was unexpectedly lower in the fumigated than in the nonfumigated soil while the growth of P. pulmonarius showed an opposite response. Degradation performances and detoxification by both fungi in the nonfumigated soil were markedly higher than those observed in the fumigated one. Heterotrophic bacterial counts in nonfumigated soil augmented with either B. rhodina or P. pulmonarius were significantly higher than those of the corresponding incubation control (6.7 ± 0.3 × 10⁸ and 8.35 ± 0.6 × 10⁸, respectively, vs 9.2 ± 0.3 × 10⁷). Bacterial communities of both incubation controls and fungal-augmented soil were compared by numerical analysis of denaturing gradient gel electrophoresis profiles of polymerase chain reaction (PCR)-amplified 16S ribosomal RNA (rRNA) genes and cloning and sequencing of PCR-amplified 16S rRNA genes. Besides increasing overall diversity, fungal augmentation led to considerable qualitative differences with respect to the pristine soil.     

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.     

Quantification of Sulfate-reducing Bacteria in Industrial Wastewater,by Real-time Polymerase Chain Reaction (PCR) Using <Emphasis Type="Italic">dsrA</Emphasis> and <Emphasis Type="Italic">apsA</Emphasis> Genes

Real-time polymerase chain reaction (PCR) is considered a highly sensitive method for the quantification of microbial organisms in environmental samples. This study was conducted to evaluate real-time PCR with SybrGreen detection as a quantification method for sulfate-reducing bacteria (SRB) in industrial wastewater produced by several chemical industries. We designed four sets of primers and developed standard curves based on genomic DNA of Desulfovibrio vulgaris from pure culture and on plasmids containing dissimilatory sulfate reductase (dsrA) or adenosine-5′-phosphosulfate reductase (apsA) genes of SRB. All the standard curves, two for dsrA and two for apsA genes, had a linear range between 0.95 × 10² and 9.5 × 10⁶ copies/μL and between 1.2 × 10³ and 1.2 × 10⁷ copies/μL, respectively. The theoretical copy numbers of the tenfold dilutions of D. vulgaris genomic DNA were best estimated (between 2.7 to 10.5 times higher than theoretical numbers) by the standard curve with DSR1F and RH3-dsr-R primers. To mimic the effect of foreign DNA in environmental samples, serial dilutions of D. vulgaris genomic DNA were mixed with Escherichia coli chromosomal DNA (40 ng per assay). This influenced neither PCR amplification nor the quantification of target DNA. Industrial wastewater was sampled during a 15-month period and analyzed for the presence of SRB, based on dsrA gene amplification. SRB displayed a higher abundance during the summer (about 10⁷–10⁸ targets mL⁻¹) and lower during the winter (about 10⁴–10⁵ targets mL⁻¹). The results indicate that our real-time PCR approach can be used for detection of uncultured SRB and will provide valuable information related to the abundance of SRB in durable environmental samples, such as complex and saline industrial wastewaters.     

Screening of high-yielding biocontrol bacterium Bs<Emphasis Type="Italic">-</Emphasis>916 mutant by ion implantation

Bacillus subtilis 916 was an effective biocontrol agent in control rice sheath blight caused by Rhizoctonia solani. To further improve its antagonistic ability, low-energy ion implantation was applied in Bs-916. We studied the effects of different doses of N⁺ implantation. The optimum dose of ion implantation for the Bs-916 was from 15 × 2.6 × 10¹⁴ N⁺/cm² to 25 × 2.6 × 10¹⁴ N⁺/cm². The mutant strain designated as Bs-H74 was obtained, which showed higher inhibition activity in the screening plate. Its inhibition zone against the indicator organism increased by 30.7% compared to the parental strain. The control effect of rice sheath blight was improved by 14.6% over that of Bs-916. Thin-layer chromatography and high-performance liquid chromatography analysis indicated that lipopeptides produced by Bs-916 and the mutant strains belonged to the surfactin family. Bs-H74 produced approximately 3.0-fold surfactin compared to that of Bs-916. To determine the role of surfactin in biocontrol by Bs-916, we tested another mutant strain, Bs-M49, which produced lower levels of surfactin significantly, and found that Bs-M49 had no obvious effects against R. solani. These results suggested that the surfactin produced by Bs-916 plays an important role in the suppression of sheath blight. These observations also showed that the Bs-H74 mutant strain is a better biocontrol agent than the parental strain.     

Placental Alpha Hemoglobin Stabilizing Protein (AHSP) and recurrent miscarriage

AHSP inhibits cellular production of the reactive oxygen species. Reduced AHSP indicates reduced protection against oxidative stressors. Our objective was to investigate AHSP levels in recurrent miscarriage (RM). Trophoblast was collected from women of 10 weeks gestation: voluntary abortion controls (VA, n = 10); spontaneous first miscarriage with subsequent normal pregnancy (SMSN, n = 15) or with subsequent miscarriage (SMSM, n = 5); RM previously investigated (RMPS, n = 5) or not previously investigated (RM, n = 5). AHSP mRNA and protein were determined using real-time quantitative polymerase chain reaction (PCR) and Western blot, respectively. One-way ANOVA was performed to assess statistical significance (p < 0.05). ahsp mRNA levels were maximally reduced in RM and RMPS (8.0 × 10⁻⁶ ± 1.3 and 8.1 × 10⁻⁶ ± 0.7, respectively) compared with SMSN and VA (16.1 × 10⁻⁶ ± 2.3 and 26.1 × 10⁻⁶ ± 2.7, respectively). SMSM showed levels significantly reduced as well (9.0 × 10⁻⁶ ± 2.3). In RM, a reduced defense from oxidative stressors is evident at first miscarriage, identifying women at high risk for subsequent eventful pregnancy. Reduced AHSP may identify women at risk of experiencing further miscarriages. Monica Emanuelli and Monia Cecati contributed equally to this paper.     

Transfer of megaplasmid pKB1 from the rubber-degrading bacterium <Emphasis Type="Italic">Gordonia westfalica</Emphasis> strain Kb1 to related bacteria and its modification

Because engineering of the 101.016-bp megaplasmid pKB1 of Gordonia westfalica Kb1 failed due to the absence of an effective transfer system, pKB1 was transferred by conjugation from G. westfalica Kb1 to a kanamycin-resistant mutant of Rhodococcus opacus PD630 at a frequency of about 6.2 × 10⁻⁸ events per recipient cell. Furthermore, pKB1 was transferred to G. polyisoprenivorans strains VH2 and Y2K and to Mycobacterium smegmatis by electroporation at frequencies of 5.5 × 10³, 1.9 × 10³, and 8.3 × 10² transformants per microgram plasmid DNA. The pKB1-encoded cadmium resistance gene cadA was used for selection in these experiments. Recombinant pKB1-containing G. polyisoprenivorans VH2 and M. smegmatis were then used to engineer pKB1. A kanamycin resistance cassette was inserted into the pKB1-encoded cadA gene, ligated to suicide plasmid pBBR1MCS-5, and the resulting plasmid was electroporated into plasmid-harboring strains. Homologous recombination between cadA on suicide plasmid and the respective sequence in pKB1 led to its integration into pKB1. Thus, two selection markers were accommodated in pKB1 to monitor plasmid transfer into Gordonia and related taxa for analysis of genes essential for rubber degradation and others. In this study, two transfer methods for large plasmids and strategies for engineering of pKB1 were successfully applied, thereby, extending the tool box for Gordonia.     

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     

Inhibition of degradation and aggregation of recombinant human consensus interferon-α mutant expressed in <Emphasis Type="Italic">Pichia pastoris</Emphasis> with complex medium in bioreactor

The methylotrophic yeast Pichia pastoris has been used for the expression of many proteins. However, limitations such as protein degradation and aggregation became obvious when secreting heterologous protein-recombinant human consensus interferon-α mutant. Here, we investigate the effect of induction temperature on the yield and stability of interferon mutant expressed by P. patoris with buffered complex medium. The best results in terms of interferon mutant bioactivity and specific bioactivity were obtained when the microorganism was induced at 15°C, which were 2.91 × 10⁸ ± 0.3 × 10⁸ and 2.26 × 10⁸± 0.23 × 10⁸ IU mg⁻¹, respectively. At the same time, the cells grew fast owing to high AOX1-specific activity, and interferon mutant expression level reached 1.23 g l⁻¹, which was almost 30 times higher than that in the flask. Also, the proteolytic degradation of interferon mutant was inhibited completely because of lower protease bioactivity probably due to a reduced cell death rate at lower temperatures as well as protection of yeast extract and peptone in complex medium. In addition, interferon mutant aggregation was repressed significantly by the addition of Tween-80, and a specific bioactivity of 7.35 × 10⁸ ± 0.56 × 10⁸ IU mg⁻¹ was obtained. These results should be applicable to other low-stability recombinant proteins expressed in P. pastoris.     

Optimization of protoplast yields from the red algae <Emphasis Type="Italic">Gracilaria dura</Emphasis> (C. Agardh) J. Agardh and G. <Emphasis Type="Italic">verrucosa</Emphasis> (Huds.) Papenfuss

This study reports on the optimization of protoplast yield from two important tropical agarophytes Gracilaria dura and Gracilaria verrucosa using different cell-wall-degrading enzymes obtained from commercial sources. The conditions for achieving the highest protoplast yield was investigated by optimizing key parameters such as enzyme combinations and their concentrations, duration of enzyme treatment, enzyme pH, mannitol concentration, and temperature. The significance of each key parameter was also further validated using the statistical central composite design. The enzyme composition with 4% cellulase Onozuka R-10, 2% macerozyme R-10, 0.5% pectolyase, and 100 U agarase, 0.4 M mannitol in seawater (30‰) adjusted to pH 7.5 produced the highest protoplast yields of 3.7 ± 0.7 × 10⁶ cells g⁻¹ fresh wt for G. dura and 1.2 ± 0.78 × 10⁶ cells g⁻¹ fresh wt for G. verrucosa when incubated at 25°C for 4–6 h duration. The young growing tips maximally released the protoplasts having a size of 7–15 μm in G. dura and 15–25 μm in G. verrucosa, mostly from epidermal and upper cortical regions. A few large-size protoplasts of 25–35 μm, presumably from cortical region, were also observed in G. verrucosa.     

EST-derived single nucleotide polymorphism markers for assembling genetic and physical maps of the barley genome

In a panel of seven genotypes, 437 expressed sequence tag (EST)-derived DNA fragments were sequenced. Single nucleotide polymorphisms (SNPs) that were polymorphic between the parents of three mapping populations were mapped by heteroduplex analysis and a genome-wide consensus map comprising 216 EST-derived SNPs and 4 InDel (insertion/deletion) markers was constructed. The average frequency of SNPs amounted to 1/130 bp and 1/107.8 bp for a set of randomly selected and a set of mapped ESTs, respectively. The calculated nucleotide diversities (π) ranged from 0 to 40.0 × 10⁻³ (average 3.1 × 10⁻³) and 0.52 × 10⁻³ to 39.51 × 10^–3 (average 4.37 × 10⁻³) for random and mapped ESTs, respectively. The polymorphism information content value for mapped SNPs ranged from 0.24 to 0.50 with an average of 0.34. As expected, combination of SNPs present in an amplicon (haplotype) exhibited a higher information content ranging from 0.24 to 0.85 with an average of 0.50. Cleaved amplified polymorphic sequence assays (including InDels) were designed for a total of 87 (39.5%) SNP markers. The high abundance of SNPs in the barley genome provides avenues for the systematic development of saturated genetic maps and their integration with physical maps. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Both R. Kota and R.K. Varshney contributed equally to this work.     

Kinetics and thermodynamics of peroxidase- and laccase-catalyzed oxidation of N-substituted phenothiazines and phenoxazines

N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k _cat/K _m) varied from 1 ×10⁷M⁻¹s⁻¹to 2.6×10⁸M⁻¹s⁻¹ at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable groups with pK _a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent bimolecular rate constants varied from 1.8×10⁵M⁻¹s⁻¹ to 2.0×10⁷M⁻¹s⁻¹ at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO, fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×10⁸M⁻¹s⁻¹ and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×10⁷M⁻¹s⁻¹ and 0.29 eV. Received: 20 September 1999 / Accepted: 24 February 2000     

Kinetics of Phase Separation of Oat β-Glucan/Whey Protein Isolate Binary Mixtures

The kinetics of phase separation and microstructure of oat β-glucan/whey protein binary mixtures varying in concentration (4–16% w/v protein, 0.3–1.2% w/v β-glucan) and β-glucan molecular weight (1.3 × 10⁶, 640 × 10³, 180 × 10³, and 120 × 10³ g/mol) was investigated by turbidimetry and fluorescent microscopy. The phase separation of the mixed systems was followed at pH 7.0 and at room temperature under quiescent conditions. Application of first principles revealed that phase separation of the systems follows first-order kinetics. Acceleration of the phase-separation process was observed with increase of β-glucan concentration for the three lowest-MW samples but the highest molecular weight (1.3 × 10⁶ g/mol) exhibited the opposite trend. Changes in the polysaccharide molecular weight resulted in considerable differences in β-glucan aggregate morphology in the mixed systems. The change in the continuity of the mixed system from polysaccharide-, to bi-, to protein-continuous was confirmed for a wide range of mixed systems differing in biopolymer concentration, and β-glucan molecular weight.     

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