Trehalose production in Escherichia coli DH5 alpha was explored by overexpressing otsBA operon encoding trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase. Production and subsequent degradation of trehalose resulted in low production of trehalose in engineered cells overexpressing otsBA, which was primarily due to the concomitant expression of endogenous trehalase. Through an in vitro enzyme assay and flask cultures of engineered cells, trehalase expression was shown to be directly related to the expression of otsBA rather than osmotic stress. Validamycin A effectively inhibited E. coli trehalase and the intracellular accumulation of trehalose was markedly enhanced in the presence of validamycin A at an optimal concentration in the medium. The trehalose production was further increased upon growth in a hypertonic medium in the presence of validamycin A. with most trehalose accumulating as an intracellular product. The highest titer was obtained when otsBA expression was induced by a medium-copy vector, ptrc99A, with 0.5 mM of isopropyl beta-D-1-thiogalactopyranoside. Trehalose titer was 1.7 g/L in controlled bioreactor cultures using synthetic M9 medium supplemented with 40 g/L glycerol, 0.1 mM validamycin A, and 300 mM NaCl. (C) 2011, The Society for Biotechnology, Japan. All rights reserved.