Streptomyces are well-known producers of valuable secondary metabolites which include a large variety of antibiotics and important model organisms for developmental studies in multicellular bacteria. The conserved transcriptional regulator AdpA of Streptomyces exerts a pleiotropic effect on cellular processes, including the morphological differentiation and biosynthesis of secondary metabolites.

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According to recent reports, bacterial chromosomes exhibit a hierarchical organization. The number of proteins that bind DNA are responsible for local and global organization of the DNA ensuring proper chromosome compaction. Advanced molecular biology techniques combined with high-throughput DNA sequencing methods allow a precise analysis of bacterial chromosome structures on a local and global scale. Methods such as in vivo footprinting and ChIP-seq allow to map binding sites of analyzed proteins in certain chromosomal regions or along the whole chromosome while analysis of the spatial interactions on global scale could be performed by 3C techniques. Additional insight into complex structures created by chromosome-organizing proteins is provided by high-resolution fluorescence microscopy techniques.

In this work the subC gene from Bacillus licheniformis encoding subtilisin was cloned into the nisin-controlled expression (NICE) vectors (pNZ8048 and pNZ8148) with or without the signal peptide SP Usp45 directing extracellular secretion via Sec machinery. Extracellular protease production and activity was tested using Lactococcus lactis NZ9000 as host, which could be used for rennet production. The efficiency of protein production was tested using purified nisin and the supernatant of L. lactis NZ970 nisin producer. Similar results were obtained for 1 ng/ml nisin and 10 000 diluted supernatant. SP Usp45 signal peptide effectively directed extracellular localization of active and stable protease. SubC signal for extracellular localization in B. licheniformis, was also recognized by L. lactis Sec pathway, although with lower efficiency, as shown by a 3-fold lower protease activity in the medium. Protease production and activity was optimized using parameters such as induction time, nutrients (glucose, casitone) supplementation during growth or protease stabilization by calcium ions. The results were also verified in fed-batch bioreactor for further scale-up of the expression system.