The Isolation and Characterization of Type II Polyketides from Soil Metagenomes; Addressing the shortage of effective antibiotics by a new method of antibiotic discovery

Antibiotic-resistance has emerged as one of the major public health problems of the 21st century. The rate at which novel antibiotics are discovered has declined for over thirty years, while simultaneously the number of antibiotic resistant strains of harmful bacteria has risen. Natural products or synthetic variations of such account for about two-thirds of all FDA approved drugs. However, the standard drug discovery platform – growing and extracting liquid bacterial cultures – has become ineffective as 99% of microbes cannot be grown in the laboratory. A novel culture-free technique allows access by heterologous expression to the biosynthetic pathways of these unculturable microbes by extracting DNA directly from the environment. In the current work, three heterologously expressed bacterial type II polyketide pathways were examined for the production of new molecules. Extraction of liquid cultures and analysis by LCMS revealed the presence of clone-specific metabolites in all three pathways. Purification by HPLC and silica flash chromatography were attempted with varying degrees of success, and the product of one incomplete pathway was successfully characterized by 1-D and 2-D NMR

Doppler sonographic indices in diagnosing the nutcracker phenomenon in a hematuric adolescent

Compression of the left renal vein between the aorta and the superior mesenteric artery, known as the nutcracker phenomenon, may cause gross or microscopic hematuria, pain in the flank, proteinuria, or a combination of these symptoms. We report the case of a hematuric adolescent diagnosed with a high index of suspicion by noninvasive Doppler sonography using the diagnostic indices of Doppler sonography established for adults with hematuria. Compression of the patient's left renal vein at the aortomesenteric portion and dilatation at the hilar portion were visualized by magnetic resonance angiography, which verified the diagnosis. (C) 2003 Wiley Periodicals, Inc

Natural Product Discovery through Improved Functional Metagenomics in <i>Streptomyces</i>

Because the majority of environmental bacteria are not easily culturable, access to many bacterially encoded secondary metabolites will be dependent on the development of improved functional metagenomic screening methods. In this study, we examined a collection of diverse <i>Streptomyces</i> species for the best innate ability to heterologously express biosynthetic gene clusters. We then optimized methods for constructing high quality metagenomic cosmid libraries in the best <i>Streptomyces</i> host. An initial screen of a 1.5 million-membered metagenomic library constructed in <i>Streptomyces albus</i>, the species that exhibited the highest propensity for heterologous expression of gene clusters, led to the identification of the novel natural product metatricycloene (<b>1</b>). Metatricycloene is a tricyclic polyene encoded by a reductive, iterative polyketide-like gene cluster. Related gene clusters found in sequenced genomes appear to encode a largely unexplored collection of structurally diverse, polyene-based metabolites