Discovery of a family of γ-aminobutyrate ureas via rational derepression of a silent bacterial gene cluster

Gaburedins, a family of γ-aminobutyrate (GABA)-derived ureas, have been discovered by deletion of gbnR, an arpA-like putative transcriptional repressor in Streptomyces venezuelae ATCC 10712. Comparison of metabolite profiles in the wild type and mutant strains revealed six metabolites in the mutant that are lacking from the wild type. The structure of gaburedin A was established by HRMS combined with 1- and 2-D NMR spectroscopy and was confirmed by total synthesis. The other metabolites were confirmed as congeners using HRMS, MS/MS and feeding of putative biosynthetic precursors. Two genes, gbnA and gbnB, are proposed to be involved in gaburedin biosynthesis. Consistent with this hypothesis, deletion of gbnB in the gbnR mutant abolished gaburedin production. This is the first report to disclose the discovery of novel natural products via rational deletion of a putative pathway-specific regulatory gene

New Insights into Chloramphenicol Biosynthesis in Streptomyces venezuelae ATCC 10712

Comparative genome analysis revealed seven uncharacterized genes, sven0909 to sven0915, adjacent to the previously identified chloramphenicol biosynthetic gene cluster (sven0916–sven0928) of Streptomyces venezuelae strain ATCC 10712 that was absent in a closely related Streptomyces strain that does not produce chloramphenicol. Transcriptional analysis suggested that three of these genes might be involved in chloramphenicol production, a prediction confirmed by the construction of deletion mutants. These three genes encode a cluster-associated transcriptional activator (Sven0913), a phosphopantetheinyl transferase (Sven0914), and a Na(+)/H(+) antiporter (Sven0915). Bioinformatic analysis also revealed the presence of a previously undetected gene, sven0925, embedded within the chloramphenicol biosynthetic gene cluster that appears to encode an acyl carrier protein, bringing the number of new genes likely to be involved in chloramphenicol production to four. Microarray experiments and synteny comparisons also suggest that sven0929 is part of the biosynthetic gene cluster. This has allowed us to propose an updated and revised version of the chloramphenicol biosynthetic pathway

Regulation of antibiotic production in Actinobacteria: new perspectives from the post-genomic era

The antimicrobial activity of many of their natural products has brought prominence to the Streptomycetaceae, a family of Gram-positive bacteria that inhabit both soil and aquatic sediments. In the natural environment, antimicrobial compounds are likely to limit the growth of competitors, thereby offering a selective advantage to the producer, in particular when nutrients become limited and the developmental programme leading to spores commences. The study of the control of this secondary metabolism continues to offer insights into its integration with a complex lifecycle that takes multiple cues from the environment and primary metabolism. Such information can then be harnessed to devise laboratory screening conditions to discover compounds with new or improved clinical value. Here we provide an update of the review we published in NPR in 2011. Besides providing the essential background, we focus on recent developments in our understanding of the underlying regulatory networks, ecological triggers of natural product biosynthesis, contributions from comparative genomics and approaches to awaken the biosynthesis of otherwise silent or cryptic natural products. In addition, we highlight recent discoveries on the control of antibiotic production in other Actinobacteria, which have gained considerable attention since the start of the genomics revolution. New technologies that have the potential to produce a step change in our understanding of the regulation of secondary metabolism are also described

Cloning, sequencing and analysis of spirotetronate biosynthetic gene clusters

Spirotetronate antibiotics are natural products that have been shown to have a broad spectrum of biological activities, including antiviral, antibacterial, antitumor and antimalarial activities. Two representatives of this group are quartromicins and chrolactomycin, which are produced by Amycolatopsis orientalis and Streptomyces sp. 569N-3 respectively. Based on other related natural products with known biosynthetic pathways, the biosynthetic routes for quartromicins and chrolactomycin were proposed and several strategies for locating the putative gene clusters directing the biosynthesis of these natural products were used. An FkbH-like protein was proposed to be specifically involved in the biosynthetic incorporation of a glycerol-derived three-carbon unit into the tetronate moieties of quartromicins and chrolactomycin. It was selected as a target to locate the biosynthetic gene clusters of tetronate natural products. After aligning sequences of known FkbH-like proteins, a set of degenerate oligonucleotide primers for amplification of fkbH-like genes was designed and tested. Fragments of fkbH-like sequences were amplified from several available strains and sequenced. Several genomic libraries were created and screened by PCR using the degenerate fkbH primers. After validating the library, clones containing the putative biosynthetic gene cluster were identified and sequenced. The obtained sequence data was then assembled and analysed. Coding sequences were identified, protein functions assigned and a biosynthetic route was proposed for the biosynthesis of quartromicins and chrolactomycin

Use of Fracture Risk Assessment Tool in clinical practice and Fracture Risk Assessment Tool future directions

Fracture Risk Assessment Tool is a free, online fracture risk calculator which can be used to predict 10-year fracture risk for women and men over age 50 years. It incorporates seven clinical risk factors and bone density to give a 10-year risk of major osteoporotic fracture and hip fracture. This dynamic tool can be used with patients at the bedside to help guide treatment decisions. There are some limitations to Fracture Risk Assessment Tool, with the most central limitation being the fact that inputs are binary. Much research has been done to try to refine Fracture Risk Assessment Tool to allow for more accurate risk prediction, and this article describes the data for adjusting Fracture Risk Assessment Tool depending on the clinical scenario such as the dose of glucocorticoid use, presence of diabetes and others. Recently, the new FRAXplus tool has been developed to address many of these concerns and will likely replace the old Fracture Risk Assessment Tool in the future. At the current time, it is available in beta form