Effect of sulfur availability on the integrity of amino acid biosynthesis in plants

Amino acid levels in plants are regulated by a complex interplay of regulatory circuits at the level of enzyme activities and gene expression. Despite the diversity of precursors involved in amino acid biosynthesis as providing the carbon backbones, the amino groups and, for the amino acids methionine and cysteine, the sulfhydryl group and despite the involvement of amino acids as substrates in various downstream metabolic processes, the plant usually manages to provide relatively constant levels of all amino acids. Here we collate data on how amino acid homeostasis is shifted upon depletion of one of the major biosynthetic constituents, i.e., sulfur. Arabidopsis thaliana seedlings exposed to sulfate starvation respond with a set of adaptation processes to achieve a new balance of amino acid metabolism. First, metabolites containing reduced sulfur (cysteine, glutathione, S-adenosylmethionine) are reduced leading to a number of downstream effects. Second, the relative excess accumulation of N over S triggers processes to dump nitrogen in asparagine, glutamine and further N-rich compounds like ureides. Third, the depletion of glutathione affects the redox and stress response system of the glutathione-ascorbate cycle. Thus, biosynthesis of aromatic compounds is triggered to compensate for this loss, leading to an increased flux and accumulation of aromatic amino acids, especially tryptophan. Despite sulfate starvation, the homeostasis is kept, though shifted to a new state. This adaptation process keeps the plant viable even under an adverse nutritional status.

Effect of spray drying temperature of yoghurt on the survival of starter cultures, moisture content and sensoric properties of yoghurt powder

A synergistic set of the strains Lactobacillus delbrueckii subsp. bulgaricus 151 and Streptococcus thermophilus MK-10 was preserved with the method of spray drying. Studies were performed on the effect of outlet air temperature in range of 60-80 degrees C upon the survival of yoghurt cultures, as well as the moisture content and sensoric properties of yoghurt powder. Survival of yoghurt cultures was the highest at 60 and 65 degrees C, but excessive moisture (10.2%) of yoghurt powder had a negative effect on its texture. Moisture content of the powder was low at 80 degrees C (4.4%), unfortunately sensoric faults appeared at this temperature, and survival of bacteria cultures decreased considerably. Temperatures within the range 70-75 degrees C ensured satisfactory survival of yoghurt cultures (L. delbrueckii subsp. bulgaricus--13.7-15.8%; S. thermophilus--51.6-54.7%), maintained proportion of the strains (L:S--1:3), satisfactory moisutre content (5.1-6.3%), and good sensoric properties of yoghurt powder.

Interaction of Bifidobacterium and Salmonella during associated growth

Interaction of 15 Bifidobacterium (belonging to species B. animalis, B. globosum and B. breve) and six Salmonella (belonging to species S. enteritidis and S. typhimurium) strains was examined during associated growth at optimum conditions for the two genera. All strains of Bifidobacterium investigated were antagonistic to Salmonella. Three strains of Bifidobacterium bactericidal to Salmonella were identified. The kinetics of Salmonella inhibition was as follows: growth of Salmonella was inhibited before the end of the exponential phase, then succeeded by a rapid decrease of live-cell numbers at the beginning of the stationary phase, after which the cell death rate was lower. Growth of Bifidobacterium in the associated cultures was similar to that in monocultures.

The heterogeneity of bovine IgG2--III. The ion-exchange heterogeneity of IgG2a is the result of VH-region variation

Bovine IgG2a from an animal homozygous at the A-locus could be fractionated on DEAE columns into subpopulations; studies using analytical size columns showed that the number of subpopulations was dependent on the ionic strength of equilibration buffer. Subpopulations of IgG2a could be purified by this method which did not differ in their carbohydrate content but had mean Ips consistent with their elution behavior. The spectrotype of their H-chains but not their L-chains, paralleled the spectrotype of the corresponding intact IgG2a subpopulations. When papain digests of each subpopulation were fractionated by chromatofocusing, their Fc fragments eluted homogeneously with a pI ca 6.0 while their Fabs eluted heterogeneously with pIs ranging from 8 to 5. The distribution of carbohydrate among such fractions corresponded to the distribution of the Fcs. The behavior of the IgG2a Fabs on chromatofocusing paralleled the elution behavior of the parent IgG2a subpopulations from DEAE-Sephadex and the isoelectric behavior of their H-chains. The antibody activity of Fab fragments, separated by chromatofocusing, are consistent with the concept of idiotypic variation. The differential antibody activity of each intact IgG2a subpopulation for seven different antigens suggests that the ion-exchange behavior of IgG2a, in which the influence of allotypes and sub-isotypes has been excluded and for which charge-related L-chain heterogeneity is minimal, must reside in the VH-regions of the different IgG2a subpopulations. Investigators are cautioned against assigning ruminant subclass designations on the basis of subpopulations isolated by ion-exchange chromatography.

The isotypic, allotypic and idiotypic heterogeneity of bovine IgG2

The antigenic heterogeneity of bovine IgG2 observed by single radial diffusion, when different cattle sera are tested with a panel of IgG2-specific reagents, was examined by a combination of biochemical and serological assays. Using an autologous anti-A1 allotypic reagent, the major antigenic heterogeneity detected by swine, rabbit and goat anti-IgG2 reagents was due to their propensity to recognize the AI allotope. All heterologous reagents and most monoclonals so far test are biased in their specificity toward this determinant. A second type of serological heterogeneity, recognized by only certain heterologous reagents, was their specificity for what we have called the IgG2b isotype of IgG2. This isotype is found in all cattle, has a restricted ion-exchange elution behaviour and does not bear a-locus allotypic determinants; molecules bearing the latter are now designated IgG2a. IgG2a elutes from anion-exchange columns in subpopulations over a wide range of ionic strength including fractions which contain IgG2b and IgG1 as well. Using IgG2a from an AI homozygous steer, these subpopulations were shown to result from idiotypic variation which appears to primarily reside in their VH-regions.

Determination of Antibiotics in Meat Using Bacillus stearothermophilus Spores

Ten parameters affecting sensitivity, accuracy and simplicity of the diffusion plate method for determining antibiotic residues in meat were evaluated with spores of Bacillus stearothermophilus as the test organism. Eight antibiotics were studied and included penicillin, bacitracin, tetracycline, chlortetracycline, oxytetracycline, streptomycin, erythromycin and neomycin. Sensitivity of the method was most influenced by concentration of inoculum, quantity of assay medium on the plate and sample size. The optimal concentration of inoculum was established as 2 × 10⁵ spores/ml of medium, quantity of the assay medium on plate/100 mm dia., as 6 ml and quantity of sample poured on disc/12.7 mm dia., as 100 μl. The pH of the assay medium was also important to both antibiotic potency and test organism growth. The activity of streptomycin and erythromycin was the most sensitive to pH variations.