The crystal and molecular structure of the alpha-helical nonapeptide antibiotic leucinostatin A

The crystal and molecular structure of the nonapeptide antibiotic leucinostatin A, containing some uncommon amino acids and three Aib residues, has been determined by x-ray diffraction analysis. The molecule crystallizes in the orthorhombic space group P2(1)2(1)2(1), a = 10.924, b = 17.810, c = 40.50 A, C62H111N11O13, HCl.H2O, Z = 4. The peptide backbone folds in a regular right-handed alpha-helix conformation, with six intramolecular i----(i + 4) hydrogen bonds, forming C13 rings. The nonapeptide chain includes at the C end an unusual beta-Ala residue, which also adopts the helical structure of the other eight residues. In the crystal the helices are linked head to tail by electrostatic and hydrogen-bond interactions, forming continuous helical rods. The crystal packing is formed by adjacent parallel and antiparallel helical rods. Between adjacent parallel helical columns there are only van der Waals contacts, while between adjacent antiparallel helical columns hydrogen-bond interactions are formed.     

A Comparison of the Use of In Vitro-Transcribed and Native rRNA for the Quantification of Microorganisms in the Environment

Abstract Nearly full-length, small subunit (SSU) rRNA was transcribed in vitro from clones of SSU rDNA genes. Comparing the use of in vitro-transcribed and native rRNA indicated that, when in vitro-transcribed rRNA was used as a standard for quantitative hybridizations with oligonucleotide probes, the population was consistently underestimated. The population abundance was expressed as a percentage of specific target SSU rRNA (determined with a specific oligonucleotide probe), relative to the total SSU rRNA (measured with a universal probe). Differences in hybridization signals could be related to specific probe target locations and rRNA denaturation conditions, suggesting that higher order structure is important in quantitative membrane hybridizations. Therefore, in vitro-transcribed rRNA cannot always be used for the absolute quantification of microbial populations, but can be employed as a standard to quantify shifts in population abundance over time, and to compare community structure in various environments.     

Fertility table and rate of population growth of the predator Supputius cincticeps (Heteroptera: Pentatomidae) on one plant of Eucalyptus cloeziana in the field

The reproductive potential and population growth (r_m and λ) of the predator Supputius cincticeps (Heteroptera: Pentatomidae) were evaluated using a life and fertility table. S. cincticeps was reared on one plant of Eucalyptus cloeziana in the field and fed with Tenebrio molitor (Coleoptera: Tenebrionidae) pupae. Females of this predator had a net reproductive rate (R₀) of 21.02 females/female; an intrinsic rate of population increase (r_m) of 0.041 and finite rate of increase (λ) of 1.042. This resulted in population growth of S. cincticeps in the eucalyptus plant with a doubling time of 17.01 days. This natural enemy can be reared under field conditions with alternative prey for use in biological control. Such individuals of S. cinticeps will be better adapted to field conditions when they are liberated.     

Mitochondrial DNA sequence variation in the spruce budworm species complex (Choristoneura: Lepidoptera)

A combination of polymerase-chain-reaction amplification and automated DNA sequencing was used to survey variation in a species complex of pest insects, the spruce budworms (Choristoneura fumiferana species group), and an outgroup species, C. rosaceana. We sequenced an mtDNA region of 1,573 bp that extends from the middle of cytochrome oxidase subunit I (COI) through tRNA leucine (UUR) to the end of cytochrome oxidase subunit II. In addition, we examined levels of intraspecific variation within a 470-bp region of the COI gene. Choristoneura fumiferana clearly represented the oldest lineage within its species group, with 2.7%-2.9% sequence divergence from the other species. In contrast, the four remaining species (C. pinus, C. biennis, C. occidentalis, and C. orae) had closely related or identical mtDNA, with < 1% divergence among most of their haplotypes. Despite its older lineage and widespread geographic distribution, C. fumiferana showed significantly lower intraspecific genetic diversity than did C. occidentalis. Choristoneura orae shared haplotypes with C. occidentalis and C. biennis, and species-level separation of these three species was not supported. Two divergent, uncommon haplotypes were also found in C. occidentalis and C. biennis. The divergent haplotype in C. biennis had an unusually high number of inferred amino acid replacements, suggesting selective differences between mitochondrial DNA haplotypes. Transition:transversion ratios in Choristoneura paralleled those found in Drosophila; transition:transversion ratios were highest in closely related sequences but decreased with increasing sequence divergence. Nucleotide composition showed an A+T bias that was near the high end of the range known for insects. This work illustrates the potential utility of direct DNA sequencing in assessing population structures, species limits, and phylogenetic relationships among organisms that have not previously been subjected to DNA analysis.      

Insights into stereochemical features of sulphated carbohydrates: X-ray crystallographic and modelling investigations

The three-dimensional structures of the 2-, 3-, 4- and 6-monosulphatesof methyl -D-galactopyranoside have been determined by X-raycrystallography; the first two as the sodium salt, the thirdas both the sodium and potassium salts, and the fourth as apotassium salt. These represent the principal sulphated monomersof the carrageenan polysaccharides. The results extend our knowledgeof the stereochemical features, such as ring conformation, sulphategeometry, hydrogen bonding and cation co-ordination, which characterizesulphated monosaccharides. The stereochemical data have beenused to derive a mean geometry of the O-sulphate group and aset of force constants for use in molecular mechanics calculationson sulphated monosaccharides. These may be used in an extrapolationof the populations of stable conformers of related oligo- andpolysaccharides. crystal structures molecular mechanics O-sulphated carbohydrates X-ray diffraction     

A Synthetic Medium for Comparative Nutritional Studies of Lactobacilli

The composition of a synthetic medium supporting the growth of lactobacilli is given (Table 1). The medium, containing glucose, amino acids, vitamins, mineral salts, purines and pyrimidines, allows the study of nutritional requirements of different strains of lactobacilli under identical environmental conditions. It was found that all the strains tested needed L-glutamic acid, L-valine and L-leucine, and a group of them also required L-arginine, L-tyrosine and L-tryptophan. Some strains required vitamins, e.g. L. bulgaricus (pantothenic acid), L. fermenti (pantothenic acid and niacin). These results are compared with those found by others employing different media.