Biochemical mechanism of the effect of barbital on rifamycin B biosynthesis by Amycolatopsis mediterranei (M18 strain)

It is well known that 5,5-diethylbarbituric acid (barbital) in the culture medium can stimulate the production of rifamycin B by Amycolatopsis mediterranei, particularly in industrial processes. However, the mechanism by which barbital exerts this effect is unknown. Results in this work show that the barbital effect is only evident under low aeration conditions (50-ml microfermentors with 7 ml of medium, 0.08 l/h air flow). Under these conditions, cultures with barbital showed similar CO2 production (in relation to a control without barbital), but higher oxygen uptake indicated that the extra O2 consumed was used in the increased rifamycin biosynthesis. Moreover, using a resting cell system where no antibiotic is produced, it was possible to show that barbital inhibits the respiratory chain, since O2 uptake decreased by 30%. Finally, we present biochemical results that suggest that a cytochrome P450-type monoxygenase, which can use atmospheric oxygen, is induced by barbital in an industrial-type strain of A. mediterranei.     

Correlation between DNA synthesis in the second, third and fourth generations of spermatogonia and the occurrence of apoptosis in both spermatogonia and spermatocytes

In the seminiferous epithelium, both DNA synthesis and apoptosis occur at equivalent stages in various species, with apoptosis taking place mainly at the same stages as DNA replication in the second, third and fourth spermatogonial generations. As preservation of the cellular associations found at these stages may have some functional significance, it is important to determine whether there is a correlation between these cellular events. In this study, pairs of immunoperoxidase-stained adjacent testis sections from rats, mice, rabbits and cats in which either bromodeoxyuridine incorporated into the newly synthesized DNA strand (BrdU labelling) or DNA 3' end labelling of the apoptotic DNA fragments (TUNEL assay) were detected were compared. In addition, both events were analysed in double-labelled sections. These two methods revealed a clear correlation between the occurrence of DNA replication in the second to fourth generations of spermatogonia and most physiological apoptosis taking place in both spermatogonia and spermatocytes in the three different mammalian orders (Rodentia, Lagomorpha and Carnivora). This correlation may result from the synchronization of mitotic spermatogonial and meiotic spermatocyte cell cycle checkpoints operating at these stages.     

Direct determination of carbohydrates, amino acids, and antibiotics by microchip electrophoresis with pulsed amperometric detection

The separation and detection of underivatized carbohydrates, amino acids, and sulfur-containing antibiotics in an electrophoretic microchip with pulsed amperometric detection (PAD) is described. This report also describes the development of a new chip configuration for microchip electrophoresis with PAD. The configuration consists of a layer of poly(dimethylsiloxane) that contains the microfluidic channels, reservoirs, and a gold microwire, sealed to a second layer of poly(dimethylsiloxane). Example separations of carbohydrates, amino acids, and sulfur-containing antibiotics are shown. The effect of the separation and injection potentials, buffer pH and composition, injection time, and PAD parameters were studied in an effort to optimize separations and detection. Detection limits ranging from 6 fmol (5 microM) for penicillin and ampicillin to 455 fmol (350 microM) for histidine were obtained.     

Group velocity and dispersion model of coupled-cavity waveguides in photonic crystals

A theoretical model of the group velocity, dispersion parameter, and dispersion slope of coupled-cavity waveguides in photonic crystals is reported. Results arising from closed-form expressions show a good agreement with simulation results obtained by employing a plane-wave expansion method. Coupled-cavity waveguides present interesting dispersion properties that may be employed in applications such as optical signal processing, dispersion compensation, and optical delay lines.     

Determination of aniline derivatives in oils related to the toxic oil syndrome by atmospheric pressure ionization-tandem mass spectrometry

In 1981, an unknown disease appeared in Spain, the Spanish Toxic Oil Syndrome. Nowadays and despite all efforts, the etiological agent is still unknown. Early studies showed a link between this illness and the consumption of denatured rapeseed oil fraudulently processed and marketed as edible oil. Two families of aniline derivatives present in these oils (fatty acid anilides and acylated phenyl amino propanediol derivatives or PAPs) were found to be good chemical markers of toxic oils. In this work, a new method has been developed to analyze these aniline derivatives in oil samples by HPLC-MS and HPLC-MS/MS with an API source. For their quantification, three different internal standards were used, one for anilides and two for PAPs. Quantification limits were 8 ppm for anilides and 0.2 ppm for PAPs. Anilides and PAPs were found in marker-positive samples at levels up to 50,000 and 330 ppm, respectively. The relative abundance of the different fatty acid anilides and PAPs correlates with the fatty acid composition of the oils. More than 2,600 different samples were analyzed by this method in the most exhaustive screening of suspected toxic oils carried out to date.     

Contribution of starter culture to the sensory characteristics of fermented Almagro eggplants

Trial fermentations were performed using three experimental starter cultures with a view to selecting the most appropriate starter for use in the manufacture of Almagro eggplants. The lactic acid bacterial strains used in the starters had previously been isolated from spontaneous fermentations. The combined action of the obligate heterofermentative species Lactobacillus brevis and the facultative heterofermentative species L. plantarum yielded Almagro eggplants with sensory properties preferred by panelists. Conversely, another obligate heterofermentative species, namely, L. fermentum, present in certain starter formulations tested, appeared to encounter difficulty growing during fermentation and exerted little influence on the sensory characteristics of the eggplants produced.     

n-Alkane content of intramuscular lipids of Iberian fresh ham from different feeding systems and crossbreeding

n-Alkane content of intramuscular lipids (Biceps femoris muscle) of the Iberian pig have been determined. Thirty-four pigs, divided into four groups, based in the feeding system (Montanera, fed on acorns and pasture; and Pienso, fed on a concentrate feed) and in the genotype (Iberian pure pigs; and Iberian crossbred with Duroc 50%) were studied. n-Alkane content of intramuscular lipids has not been affected by neither crossbreeding nor feeding, although the analysis of feeds administered to the pigs showed greater n-alkane values in pasture (consumed by animals in montanera), than in acorns and concentrate feed.     

Isolation and sequence of the MIG1 homologue from the yeast Candida utilis

The Mig1p repressor from the food yeast Candida utilis has been isolated using a homologous PCR hybridization probe. This probe was amplified with two sets of degenerate primers designed on the basis of highly conserved motifs in the DNA-binding region (zinc-finger domain) from yeast Mig1p and fungi CreA repressors. The cloned gene was sequenced and found to encode a polypeptide of 345 amino acids which shows significant identity with other yeast and fungus repressors in the DNA-binding domain and also with the yeast Mig1 proteins in the C-terminal region (effector domain). The MIG1 repressor gene from C. utilis was able to complement functionally the mig1 mutation of S. cerevisiae. The sequence presented here has been deposited in the EMBL data library under Accession No. AJ277830.     

用有机掺杂硅酸盐法制备稳定的pH传感膜

采用溶胶-凝胶法制备基于染料吸收原理的光纤化学pH传感膜.通过有机掺杂,获得了对溶液pH具有宽范围动态响应的敏感膜.将四乙氧基硅烷和有机硅单体水解后加入pH指示剂,铺成溶胶-凝胶薄膜.该pH传感器的pH感应范围可达到pH3～11,响应速度3 min,一个月稳定性在RSD＜18%.