Effect of fermentation conditions on N2 fixation by Methylococcus capsulatus

Nitrogen fixation has been investigated during chemostat fermentations with a culture of Methylococcus capsulatus with natural gas. It is demonstrated that nitrogen fixation occurs under conditions when either nitrate or ammonia as nitrogen source is insufficient for the growth on fixed supply of methane and oxygen. The fixation occurs contrary to expectations within a wide range of dilution rates and with variation of concentration of liquid source of nitrogen. An O₂ optimum is determined for the nitrogenase system of the culture in an assay. During fermentation a complete abolishment of nitrogenase reaction is attained at 15% air saturation (dissolved oxygen). Conditions for N₂ fixation is unaltered with change of pH from 6.8 to 5.7.     

Mycoplasma hyopneumoniae and Mycoplasma hyosynoviae Infection in Cases of Fibrinous Pericarditis in Slaughter Pigs

Pericarditis, acute or subacute, is found at post mortem meat inspection of baconers in about 0.02 to 0.04% of slaughtered pigs in Denmark. The pathological findings are usually restricted to the pericardial sac. The pericardial sac is filled with a fibrinous exudate, which may be blood stained. In some cases massive granulation tissue formation is seen underlying the fibrinous exudate. Other constantly occurring, but less aggravating lesions, are chronic catarrhal bronchopneumonia and increased volume of serosanguinous synovial fluid in the large joints of the limbs. Lesions usually seen as sequelae to septicaemia have not been observed. The lesions seem to be part of a pathological entity which may be involved in the pathogenesis of fibrinous pericarditis in baconers.     

Polyphosphate accumulation among denitrifying bacteria in activated sludge

Bacterial polyphosphate accumulation and denitrification are important processes in biological removal of nutrients from wastewater. It has been suggested that phosphorus accumulators are able to denitrify. However, the bacteria known as the most important phosphorus accumulators, belonging to the genus Acinetobacter are generally not known to denitrify. To clarify how commonly both physiological traits are present in the same organism, we screened 165 isolates from activated sludge and wastewater for their ability to denitrify, and the ability of the denitrifying isolates to accumulate polyphosphate. Of the 165 isolates, 149 were from acetate mineral medium (87 of these identified as Acinetobacter by the API 20 NE identification system) and 16 were from nutrient broth and nitrate medium. Only 15 of 165 isolates tested showed true respiratory denitrification activity. In the presence of acetylene they converted more than 80% of 5mM NO3- to N2O in 6 days. None of the Acinetobacter isolates were among the 15 respiratory denitrifiers. The denitrifying isolates were identified as species of Pseudomonas, Agrobacterium, Pasteurella, Sphingomonas or could not be identified by the API 20 NE identification system. According to the BIOLOG identification system the denitrifiers were species of Pseudomonas, Hydrogenophaga, Citrobacter, Xanthomonas or they could not be identified. The ability of confirmed denitrifiers to accumulate phosphate was measured in experiments where cells pregrown under phosphorus limitation were exposed to phosphate (8 mg P/L) under aerobic conditions. The rates of excess phosphate uptake varied from 0.3 to more than 23 mg P/g dry matter/h. Rates for four isolates were higher than those reported for Acinetobacter strains. These results show that polyphosphate accumulation and denitrification in activated sludge can be carried out by the same organisms.     

Evaluation of mass spectrometric techniques for charaterization of engineered proteins

A simple and versatile method of in vitro site-specific mutagenesis based on polymerase chain reaction (PCR) is described. The complete method required the use of three oligonucleotide primers and two PCRs. The product of the first PCR was used as one of the primers (megaprimer) in the second PCR. Essentially 100% of the final product incorporated the desired mutation. The various aspects of the procedure and its application is described in detail.     

Inhibitory effect of lignin by-products of pulping on yeast growth

The antimicrobial properties of lignin by-products obtained by organic solvent, neutral sulfite semichemical and kraft pulping were shown in a series of yeasts. Lignin can act as an inhibitor of growth ofSporobolomyces roseus, Candida tropicalis, Trichosporon cutaneum andCandida albicans. Oxidation of all lignin samples tested depresses their inhibitory effects.     

A hydroxyproline-containing class IV chitinase of sugar beet is glycosylated with xylose

Two acidic chitinase isoforms, SP1 and SP2, have been purified to homogeneity from leaves of sugar beet (Beta vulgaris) infected with Cercospora beticola. SP1 and SP2 are extracellular proteins with an apparent molecular mass of 35 kDa and an approximate pI of 4.2. Since the only major difference was slightly diverging M _r's, only the SP2 chitinase was further characterized. Partial amino acid sequence data for SP2 was used to generate a polymerase chain reaction (PCR) clone employed for the isolation of a cDNA clone encoding SP2. SP2 exhibits significant structural identity with the class IV chitinases from sugar beet, rapeseed, bean and maize, but differs from the other members of this class in having a longer hinge region, comprising 22 amino acid residues, with a repeated TTP motif. Western blotting analyses, using antibody raised against SP2, demonstrated an induction of SP protein during infection with C. beticola. The induction was very local, with high protein accumulation found close to the infection site only. Amino acid compositional analysis of SP2 revealed that five out of fourteen prolines are hydroxylated. No glucosamine or galactosamine residues are present. Evidence was obtained that SP2 is glycosylated with a limited number (7) of xylose residues: (1) SP2 was stained with the periodic acid-Schiff (PAS) reagent, (2) electrospray mass spectrometry on SP2 gave a series of M _r's with a consistent increase between two molecular masses of 132 Da, (3) SP2 was recognized by an antibody specific for -1,4-D-xylopyranose. The vacuolar class I chitinases A and B in tobacco have recently been shown to comprise a new class of hydroxyproline-containing proteins (Sticher et al., Science 257 (1992) 655–657). The SP2 chitinase differs from these in being glycosylated and, thus, represents a novel type of hydroxyproline-containing glycoproteins in plants.     

Carotenoids in the eyespot apparatus of the flagellate green alga Spermatozopsis similis: Adaptation to the retinal-based photoreceptor

Isolated intact eyespot apparatuses, the photoreceptive organelles involved in blue-light-mediated photoresponses of flagellate green algae, were analyzed regarding their carotenoid composition. Carotenoids from the eyespot apparatuses of Spermatozopsis similis were identified by high-performance liquid chromatography, visible-light absorption spectra, mass spectroscopy and by ¹H-nuclear magnetic resonance spectroscopy (carotenes), and compared with those of whole-cell extracts. Both extracts contained ,-carotene, ,-carotene (formerly -carotene), lycopene, lutein, zeaxanthin, violaxanthin and all-E-and 9-Z-neoxanthin. The relative carotenoid compositions, however, differed significantly. A twofold relative increase in the total carotene level was evident in the fraction enriched in eyespot apparatuses. This was mainly due to an increase in the monocyclic ,-carotene and the aliphatic lycopene, whereas the relative content of ,-carotene remained unchanged. On the other hand a relative decrease in the total xanthophyll content, especially of lutein and the epoxidic carotenoid neoxanthin, was observed in the eyespot apparatuses compared with the whole-cell extracts. The decrease of the latter resulted almost solely from a reduction of the 9-Z-rather than the all-E-isomer. The bulk of the carotenes is thought to be localized in the highly organized eyespot lipid globules, which act as a combined quarter-wave interference reflector and absorption screen for the photoreceptor in green algae. The enrichment of ,-carotene and lycopene in the eyespot apparatuses, extending the range of visible light absorption to longer wavelengths, represents an adaptation of the screen to the retinal-based photoreceptor of flagellate green algae and is one of the prerequisites for maximal directional sensitivity of the eyespot apparatus.Abbreviations ¹H-NMR nuclear magnetic resonance - IUPAC International Union of Pure and Applied Chemistry - VIS visible absorption spectra This work was supported by the Deutsche Forschungsgemeinschaft (G.K. and M.M.). M.G. was supported by a fellowship from the Norwegian Research Council of Science and Humanities.     

Determination of the overall volumetric mass transfer coefficient kLa,by a temperature dependent change of gas solubility

Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and k_La was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum k_La that can be measured by this method in a standard laboratory scale bioreactor is 145 h^–1 corresponding to a temperature change rate of 320°C h^–1.Nomenclature p Difference between p_G and p_L (% saturation) - T Ramp change of temperature (°C) - E Temperature-compensated output from the oxygen electrode (A) - E_u Uncompensated output from the oxygen electrode (A) - k_La Overall volumetric mass transfer coefficient (h^–1) - k_La_Tm Overall volumetric mass transfer coefficient at temperature T_m (h^–1) - P_G Dissolved oxygen activity in equilibrium with the gas phase (% saturation) - p_L Dissolved oxygen activity (% saturation) - p_Lm Dissolved oxygen activity at time t_m (% saturation) - t Time (h) - t_m Time of maximum p (h) - T Temperature (°C) - T_cal Calibration temperature of the oxygen electrode (°C) - T_m Final temperature after a temperature shift (°C) - T_n Temperature at time t_n     

Habitat shift in roach (Rutilus rutilus) induced by pikeperch (Stizostedion lucioperca) introduction: predation risk versus pelagic behaviour

Changes in the fish community structure and habitat use were followed after the introduction of pikeperch (Stizostedion lucioperca) to the roach-dominated Lake Gjersjøen. Quantitative echosounding showed that the density of juvenile roach (Rutilus rutilus) was dramatically reduced in pelagic areas, from 12 000–15 000 fish/ha to 250 fish/ha, while total fish density remained unchanged in littoral areas. At the same time, the habitat segregation between different size groups of roach was altered as larger roach utilized the pelagic zone after pikeperch introduction. The loss of the pelagic refuge for juvenile roach increased the availability of juvenile roach to littoral predators, notably perch. In littoral areas, the fish community changed from one dominated by roach (> 95%) to one dominated by perch (> 50%).