Streptomyces calvus is best known as the producer of the fluorinated natural product nucleocidin. This strain of Streptomycetes is also unusual for displaying a "bald" phenotype that is deficient in the formation of aerial mycelium and spores. Genome sequencing of this organism revealed a point mutation in the bldA gene that is predicted to encode a misfolded Leu-tRNA(UUA) molecule. Complementation of S. calvus with a correct copy of bldA restored sporulation and additionally promoted production of a polyeneoic acid amide, 4-Z-annimycin, and a minor amount of the isomer, 4-E-annimycin. Bioassays reveal that these compounds inhibit morphological differentiation in other Actinobacteria. The annimycin gene cluster encoding a type 1 polyketide synthase was identified and verified through disruption studies. This study underscores the importance of the bldA gene in regulating the expression of cryptic biosynthetic genes.

Drug transporters play an essential role in disposition and effects of multiple drugs. Plasma concentrations of the victim drug can be modified by drug–drug interactions occurring in enterocytes (e.g., P‐glycoprotein), hepatocytes (e.g., organic anion‐transporting polypeptide 1B1 (OATP1B1)), and/or renal proximal tubular cells (e.g., organic cation transporter 2 (OCT2)/multidrug and toxin extrusion 1 and 2‐K (MATE1/MATE2‐K)). In addition, transporter‐mediated drug–drug interactions can cause altered local tissue concentrations and possibly altered effects/toxicity (e.g., in liver and kidneys). During drug development, there is now an intensive in vitro screening of new molecular entities as transporter substrates and inhibitors, followed if necessary by drug–drug interaction studies in healthy volunteers. Nevertheless, there are still unresolved issues, which will also be discussed in this review article (e.g., the clinical significance of transporter‐mediated drug–drug interactions of particular relevance to the elderly who are prescribed multiple drugs, with additional impaired liver or kidney function, and the extent to which medication safety in real life could be improved by a reduction of those interactions).

BackgroundThe genus Saccharothrix is a representative of the family Pseudonocardiaceae, known to include producer strains of a wide variety of potent antibiotics. Saccharothrix espanaensis produces both saccharomicins A and B of the promising new class of heptadecaglycoside antibiotics, active against both bacteria and yeast.ResultsTo better assess its capabilities, the complete genome sequence of S. espanaensis was established. With a size of 9,360,653 bp, coding for 8,501 genes, it stands alongside other Pseudonocardiaceae with large genomes. Besides a predicted core genome of 810 genes shared in the family, S. espanaensis has a large number of accessory genes: 2,967 singletons when compared to the family, of which 1,292 have no clear orthologs in the RefSeq database. The genome analysis revealed the presence of 26 biosynthetic gene clusters potentially encoding secondary metabolites. Among them, the cluster coding for the saccharomicins could be identified.ConclusionS. espanaensis is the first completely sequenced species of the genus Saccharothrix. The genome discloses the cluster responsible for the biosynthesis of the saccharomicins, the largest oligosaccharide antibiotic currently identified. Moreover, the genome revealed 25 additional putative secondary metabolite gene clusters further suggesting the strain’s potential for natural product synthesis.

BackgroundAccumulating evidence indicates that trimethylamine-N-oxide (TMAO) may play a causal role in cardiovascular disease (CVD), chronic kidney disease (CKD) and type 2 diabetes (T2D). TMAO plasma concentrations show considerable intra- and inter-individual variation, underscoring the need for a reference interval in the general population to identify elevated TMAO concentrations.MethodsTMAO concentrations were determined using an LC-MS/MS assay in a community-based sample of the PopGen control cohort consisting of 694 participants (54% men; aged 25–82 years) free of clinical CVD, CKD and T2D. We defined reference intervals for TMAO concentrations in human plasma using the 2.5th and 97.5th percentiles. Using multivariable regression analysis we analyzed the association of estimated glomerular filtration rate (eGFR), sex, and dietary intake and TMAO plasma concentrations.ResultsTMAO plasma concentrations were positively skewed and differed by sex. The median TMAO plasma concentration in men was 3.91 (Q1–Q3: 2.87–6.10) μmol/L and the reference interval 1.28–19.67 μmol/L (2.5th–97.5th percentile). In women median TMAO plasma concentration was 3.56 (Q1–Q3: 2.41–5.15) μmol/L and the reference interval 1.08–17.12 μmol/L. In multivariable regression analysis plasma TMAO was associated with sex, renal function and diet. The association of TMAO and diet was significant for intake of fish and shellfish in men only.ConclusionsIn a community-based sample free of apparent CVD and renal disease, we report the distribution of TMAO plasma concentrations with sex, renal function and diet as factors associated with plasma TMAO, and suggest reference intervals. These data may facilitate standardized comparisons of TMAO across populations.

Trimethylamine-N-oxide (TMAO) gained considerable attention because of its role as a cardiovascular risk biomarker. Organic cation transporter 2 (OCT2) mediates TMAO uptake into renal proximal tubular cells. Here we investigated the potential role of multidrug and toxin extrusion protein 1 (MATE1) for translocation of TMAO across the luminal membrane of proximal tubular cells. HEK293 cells stably expressing OCT2 (HEK-OCT2) or MATE1 (HEK-MATE1) were used for uptake studies. Transcellular transport of TMAO was investigated using monolayers of MDCK control cells (MDCK-Co) as well as single- (MDCK-OCT2, MDCK-MATE1) and double-transfected cells (MDCK-OCT2-MATE1). In line with previous studies, HEK-OCT2 cells revealed a 2.4-fold uptake of TMAO compared to control cells (p < 0.001), whereas no significant uptake was observed in HEK-MATE1. In monolayers of MDCK cells, polarised TMAO transcellular transport was not significantly different between MDCK-Co and MDCK-OCT2 cells, but significantly increased in MDCK-MATE1 (p < 0.05) and MDCK-OCT2-MATE1 cells (p < 0.001). The OCT/MATE inhibitor trimethoprim abolished TMAO translocation in MDCK-OCT2-MATE1 cells (p < 0.05). The present data suggest that MATE1 contributes to renal elimination of TMAO. For selected MATE substrates, such as TMAO, uptake studies using non-polarised MATE-expressing cells can reveal false negative results compared to studies using polarised monolayers.