Global transcription profiles and intracellular pH regulation measured in Bacillus licheniformis upon external pH upshifts.

Abstract

For optimization of propagation conditions for an industrially used Bacillus licheniformis, this study examines the effect of transferring cells at the early-stationary growth phase (pH 5.3) to fresh growth medium at pH 5.0-8.0. Intracellular pH (pH(i)) was measured on a single-cell level, using fluorescence ratio imaging microscopy after staining with 5(6)-carboxyfluorescein diacetate succinimidyl ester. Transcription profiles were determined using a genome DNA microarray. The optimum extracellular pH (pH(ex)) value for growth of B. licheniformis was found to be pH 7.0, resulting in the shortest lag phase, highest maximum specific growth rate and maximum biomass formation. An average pH gradient (Delta pH = pH(i) - pH(ex)) of approx. 1.0 was found in B. licheniformis 15 min after transfer to pH(ex) 5.0-8.0. Up-regulation of genes involved in sucrose uptake at pH 7.0 could be related to the optimum growth observed. Transcription profiles indicated that the organism was experiencing phosphate starvation upon transfer to pH 7.0 and pH 8.0. Mechanisms involved in pH(i) regulation appeared to include changes in fatty acid synthesis to yield a more rigid cell membrane structure at low pH(ex) values and conversion of pyruvate to acetoin instead of acetate for neutralization of low pH(ex) values.