To develop a microbial production platform based on hydrogen and carbon dioxide, a genetic transformation system for the thermophilic acetogen Moorella thermoacetica ATCC39073 was developed. The uracil auxotrophic strain dpyrF was constructed by disrupting pyrF for orotate monophosphate decarboxylase. The transformation plasmids were methylated by restriction methylases of M. thermoacetica to avoid the decomposition of introduced plasmids by restriction-modification system. Reintroduction of native pyrF into the mutant by homologous recombination ensured recovery from uracil auxotrophy. To test heterologous gene expression in dpyrF, the lactate dehydrogenase (LDH) gene (T-ldh) from Thermoanaerobacter pseudethanolicus ATCC33223 was electroporated into dpyrF with a promoter of the glyceraldehyde-3-phosphate dehydrogenase (G3PD) gene of M. thermoacetica ATCC39073. The resulting transformant (C31) successfully transcribed T-ldh and exhibited higher LDH activity than ATCC39073 and dpyrF, yielding 6.8 mM of lactate from fructose, whereas ATCC39073 did not produce lactate. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.