Elucidation of the Streptomyces coelicolor pathway to 4-methoxy-2,2'-bipyrrole-5-carboxaldehyde, an intermediate in prodiginine biosynthesis

The biosynthetic pathway to 4-methoxy-2,2'-bipyrrole-5-carboxaldehyde (MBC), a key intermediate in the biosynthesis of prodiginine antibiotics in Streptomyces coelicolor, has been elucidated using a combination of gene replacements and feeding experiments with chemically synthesised MBC and a synthetic analogue of a pathway intermediate.     

Identification of a cluster of genes that directs desferrioxamine biosynthesis in Streptomyces coelicolor M145

Desferrioxamines are a structurally related family of tris-hydroxamate siderophores that form strong hexadentate complexes with ferric iron. Desferrioxamine B has been used clinically for the treatment of iron overload in man. We have unambiguously identified desferrioxamine E as the major desferrioxamine siderophore produced by Streptomyces coelicolor M145 and have identified a cluster of four genes (desA-D) that directs desferrioxamine biosynthesis in this model actinomycete. On the basis of comparative sequence analysis of the proteins encoded by these genes, we propose a plausible pathway for desferrioxamine biosynthesis. The desferrioxamine biosynthetic pathway belongs to a new and rapidly emerging family of pathways for siderophore biosynthesis, widely distributed across diverse species of bacteria, which is biochemically distinct from the better known nonribosomal peptide synthetase (NRPS) pathway used in many organisms for siderophore biosynthesis.     

Hot phonon-assisted electron resonant tunnelling through a donor level in a quantum well

We develop a theoretical model of resonant tunnelling assisted by non-equilibrium acoustic phonons through a donor state in a quantum well and compare the numerical results of the phonon-induced current with recent experiments. Qualitative agreement has been obtained, although the calculated amplitudes are 1–2 orders of magnitude smaller than the experimental values. A possible model to explain this is proposed.     

Discovery and Biosynthesis of Bolagladins: Unusual Lipodepsipeptides from Burkholderia gladioli Clinical Isolates**

Two Burkholderia gladioli strains isolated from the lungs of cystic fibrosis patients were found to produce unusual lipodepsipeptides containing a unique citrate-derived fatty acid and a rare dehydro-β-alanine residue. The gene cluster responsible for their biosynthesis was identified by bioinformatics and insertional mutagenesis. In-frame deletions and enzyme activity assays were used to investigate the functions of several proteins encoded by the biosynthetic gene cluster, which was found in the genomes of about 45 % of B. gladioli isolates, suggesting that its metabolic products play an important role in the growth and/or survival of the species. The Chrome Azurol S assay indicated that these metabolites bind ferric iron, which suppresses their production when added to the growth medium. Moreover, a gene encoding a TonB-dependent ferric-siderophore receptor is adjacent to the biosynthetic genes, suggesting that these metabolites may function as siderophores in B. gladioli.     

Acoustic scattering by a spherical obstacle: modification to the analytical long-wavelength solution for the zero-order coefficient

Classical long wavelength approximate solutions to the scattering of acoustic waves by a spherical liquid particle suspended in a liquid (an emulsion) show small but significant differences from full solutions at very low k(c)a (typically k(c)a < 0.01) and above at k(c)a > 0.1, where k(c) is the compressional wavenumber and a the particle radius. These differences may be significant in the context of dispersed particle size estimates based on compression wave attenuation measurements. This paper gives an explanation of how these differences arise from approximations based on the significance of terms in the modulus of the complex zero-order partial wave coefficient, A(0). It is proposed that a more accurate approximation results from considering the terms in the real and imaginary parts of the coefficient, separately.