glutamicum WT using the respective primer pairs A/B and C/D as indicated in CYC202 Additional file 3: Table S1. The PCR products were purified and linked by crossover PCR using the respective primer pair A/D (Additional file
3: Table S1). The either SmaI or BamHI restricted purified PCR product was cloned into pK19mobsacB resulting in the construction of the respective deletion vector (Additional file 3: Table S1). Targeted deletion of a carotenogenic buy Erastin gene via two-step homologous recombination using the respective deletion vector was carried out as described previously [26]. For the first recombination event integration of the vector into one of the flanking regions was selected via kanamycin resistance. Integration of the deletion vector into the genome results in a sucrose sensitivity because of the sacB gene product levansucrase. Selection for clones Compound C that have excised the deletion vector in a second recombination event was carried out via sucrose-resistance. Deletion of a carotenogenic gene was verified by PCR analysis of the constructed mutant using the respective primer pair E/F (Additional file 3: Table S1). Extraction of carotenoids from bacterial cell cultures To extract carotenoids
from the C. glutamicum strains 20 ml aliquots of the cell cultures were centrifuged at 10,000 × g for 15 min, and the pellets were washed with deionized H2O. The pigments were extracted with 10 ml methanol:acetone
mixture (7:3) at 60°C for 80 min with thorough vortexing every 20 min. When necessary, several extraction cycles were performed to remove all visible colors from the cell pellet. Analysis of carotenoids The extraction mixture was centrifuged 10,000 × g for 15 min and the methanol supernatant was transferred to a new tube. The absorption spectra of the various ex-tracts were measured at wavelengths between 400 and 800 nm using the UV-1202 spectrophotometer (Shimadzu, Duisburg, Germany). High performance liquid chromatography (HPLC) analyses of the C. glutamicum extracts were performed FAD on an Agilent 1200 series HPLC system (Agilent Technologies Sales & Services GmbH & Co. KG, Waldbronn), including a diode array detector (DAD) for UV/visible (Vis) spectrum recording. Quantification of carotenoids was performed using the extracted wavelength chromatogram at peak λmax, 450 nm for decaprenoxanthin and carotenoids with corresponding UV/Vis profiles and 470 nm for lycopene and corresponding carotenoids. Lycopene from tomato (Sigma, Steinheim, Germany) was used as standard. It was dissolved in chloroform according to its solubility and diluted in methanol. The HPLC protocol comprised isocratic elution for 25 min using a flow rate of 1.