The LIKE system, a novel protein expression toolbox for Bacillus subtilis based on the liaI promoter

Background

Bacillus subtilis is a very important Gram-positive model organism of high biotechnological relevance, which is widely used as a host for the production of both secreted and cytoplasmic proteins. We developed a novel and efficient expression system, based on the liaI promoter (P_liaI) from B. subtilis, which is under control of the LiaRS antibiotic-inducible two-component system. In the absence of a stimulus, this promoter is kept tightly inactive. Upon induction by cell wall antibiotics, it shows an over 100-fold increase in activity within 10 min.

Results

Based on these traits of P_liaI, we developed a novel LiaRS-controlled gene expression system for B. subtilis (the “LIKE" system). Two expression vectors, the integrative pLIKE-int and the replicative pLIKE-rep, were constructed. To enhance the performance of the P_liaI-derived system, site-directed mutagenesis was employed to optimize the ribosome binding site and alter its spacing to the initiation codon used for the translational fusion. The impact of these genetic modifications on protein production yield was measured using GFP as a model protein. Moreover, a number of tailored B. subtilis expression strains containing different markerless chromosomal deletions of the liaIH region were constructed to circumvent undesired protein production, enhance the positive autoregulation of the LiaRS system and thereby increase target gene expression strength from the P_liaI promoter.

Conclusions

The LIKE protein expression system is a novel protein expression system, which offers a number of advantages over existing systems. Its major advantages are (i) a tightly switched-off promoter during exponential growth in the absence of a stimulus, (ii) a concentration-dependent activation of P_liaI in the presence of suitable inducers, (iii) a very fast but transient response with a very high dynamic range of over 100-fold (up to 1,000-fold) induction, (iv) a choice from a range of well-defined, commercially available, and affordable inducers and (v) the convenient conversion of LIKE-derived inducible expression strains into strong constitutive protein production factories.

[Effect of tonometry and nasolacrimal duct irrigation on bacterial flora of the conjunctiva]

This study was undertaken to assess the influence of preoperative ophthalmological examinations on the microbial flora of the conjunctiva. For this purpose, 112 patients awaiting ocular surgery were included in the study. Conjunctival swabs for microbiological investigation were taken by nurses on the day of admission. In addition, specimens were taken before an ophthalmological examination, after applanation and impression tonometry, after irrigation of the lacrimal duct and 2 h after the end of all examinations. A last swab was taken preoperatively. Comparison of the microbiological results of the first two specimens only showed an agreement in 53% of the cases. The increase after tonometry and irrigation of the lacrimal duct in the number of swabs that were positive was not permanent. Swabs that were primarily germ-free and those that were mostly contaminated also showed strong bacterial fluctuation. Based on the present results, there is no strong evidence that the microorganisms found at the preoperative examinations correlate with a higher risk of postoperative infection. Disinfection of the conjunctival sac and the application of antibiotic drops are necessary on the day before the operation and immediately before it.