Expanding the promoter toolbox of Bacillus megaterium

Abstract

Over the past decades, Bacillus megaterium has gained significant interest in the biotechnological industry due to its high capacity for protein production. Although many proteins have been expressed efficiently using the optimized xylose inducible system so far, there is a considerable demand for novel promoters with varying activities, particularly for the adjustment of protein levels in multi-enzyme cascades. Genome-wide microarray analyses of the industrially important B. megaterium strain MS941 were applied to identify constitutive and growth phase dependent promoters for the expression of heterologous proteins from the early exponential to the early stationary phase of bacterial growth. Fifteen putative promoter elements were selected based on differential gene expression profiles and signal intensities of the generated microarray data. The corresponding promoter activities were evaluated in B. megaterium via β-galactosidase screening. β-Galactosidase expression levels ranged from 15% to 130% compared to the optimized xylose inducible promoter. Apart from these constitutive promoters we also identified and characterized novel inducible promoters, which were regulated by the addition of arabinose, galactose and the commonly used allolactose analog IPTG. The potential application of the identified promoters for biotechnologically relevant processes was demonstrated by overexpression of the cholesterol oxidase II from Brevibacterium sterolicum, thus obtaining product yields of up to 1.13 g/l/d. The provided toolbox of novel promoters offers versatile promoter strengths and will significantly contribute to harmonize protein expression in synthetic metabolic pathways, thereby pushing forward the engineering of B. megaterium as microbial cell factory for the biosynthesis and conversion of valuable compounds.