Pristinamycin production in Streptomyces pristinaespiralis Pr11 is tightly regulated by an interplay between different repressors and activators. A ␥-butyrolactone receptor gene (spbR), two TetR repressor genes (papR3 and papR5), three SARP (Streptomyces antibiotic regulatory protein) genes (papR1, papR2, and papR4), and a response regulator gene (papR6) are carried on the large 210-kb pristinamycin biosynthetic gene region of Streptomyces pristinaespiralis Pr11. A detailed investigation of all pristinamycin regulators revealed insight into a complex signaling cascade, which is responsible for the fine-tuned regulation of pristinamycin production in S. pristinaespiralis. Streptomycetes are filamentous, Gram-positive soil bacteria that are well known for their ability to produce varieties of bioactive secondary metabolites, including more than 70% of the commercially important antibiotics (1). The production of antibiotics is controlled by a vast array of physiological and nutritional conditions, communicated by extracellular and intracellular signaling molecules (2). The beginning of antibiotic biosynthesis is often coordinated with processes of morphological differentiation. The characteristic Streptomyces life cycle involves the formation of a feeding substrate mycelium and subsequent development of aerial hyphae, which finally septate into spores (3). Generally, antibiotic production begins as the culture enters stationary growth in liquid culture and coincidences with the onset of morphological differentiation in agar-grown cultures (reviewed in reference 4). In many Streptomyces strains, antibiotic production is regulated by low-molecular-weight compounds, called ␥-butyrolactone autoregulators (GBLs) (5, 6). GBLs are small diffusible signaling molecules that are synthesized and gradually accumulated in a growth-dependent manner, at or near the middle of the exponential phase of Streptomyces growth, when they trigger the onset of antibiotic biosynthesis and/or morphological differentiation at nanomolar concentrations (7). Often, the GBL signal is transmitted via a hierarchical signaling cascade including pleiotropic and pathway-specific regulators, which all together control the antibiotic production: when the GBL concentration reaches a critical level, the signal is transmitted into the cells by binding to specific cytoplasmic receptor proteins, the GBL receptors (7). GBL receptors belong to the TetR family of transcriptional regulators (8). In the absence of the corresponding ligand, the GBL receptor binds to conserved AT-rich, partially palindromic sequences (9), the so-called "ARE" sequences (autoregulatory element) (10), within the promoter regions of its target genes and thereby represses the transcription of these genes. By binding of the GBLs to their receptors, the latter undergo a conformational change and dissociate from the target DNA, allowing expression of the derepressed genes (11). Predominantly, targets of GBL receptors are transcriptional regulatory genes, such as TetR and SARP (Streptomyce...

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L-phenylglycine (L-Phg) is a rare non-proteinogenic amino acid, which only occurs in some natural compounds, such as the streptogramin antibiotics pristinamycin I and virginiamycin S or the bicyclic peptide antibiotic dityromycin. Industrially, more interesting than L-Phg is the enantiomeric D-Phg as it plays an important role in the fine chemical industry, where it is used as a precursor for the production of semisynthetic β-lactam antibiotics. Based on the natural L-Phg operon from Streptomyces pristinaespiralis and the stereo-inverting aminotransferase gene hpgAT from Pseudomonas putida, an artificial D-Phg operon was constructed. The natural L-Phg operon, as well as the artificial D-Phg operon, was heterologously expressed in different actinomycetal host strains, which led to the successful production of Phg. By rational genetic engineering of the optimal producer strains S. pristinaespiralis and Streptomyces lividans, Phg production could be improved significantly. Here, we report on the development of a synthetic biology-derived D-Phg pathway and the optimization of fermentative Phg production in actinomycetes by genetic engineering approaches. Our data illustrate a promising alternative for the production of Phgs.

Today, one of the biggest challenges in antibiotic research is a targeted prioritization of natural compound producer strains and an efficient dereplication process to avoid undesired rediscovery of already known substances. Thereby, genome sequence-driven mining strategies are often superior to wet-lab experiments because they are generally faster and less resource-intensive. In the current study, we report on the development of a novel in silico screening approach to evaluate the genetic potential of bacterial strains to produce protein synthesis inhibitors (PSI), which was termed the protein synthesis inhibitor ('psi’) target gene footprinting approach = Ψ-footprinting. The strategy is based on the occurrence of protein synthesis associated self-resistance genes in genome sequences of natural compound producers. The screening approach was applied to 406 genome sequences of actinomycetes strains from the DSMZ strain collection, resulting in the prioritization of 15 potential PSI producer strains. For twelve of them, extract samples showed protein synthesis inhibitory properties in in vitro transcription/translation assays. For four strains, namely Saccharopolyspora flava DSM 44771, Micromonospora aurantiaca DSM 43813, Nocardioides albertanoniae DSM 25218, and Geodermatophilus nigrescens DSM 45408, the protein synthesis inhibitory substance amicoumacin was identified by HPLC-MS analysis, which proved the functionality of the in silico screening approach.