Osmoregulation in the model organismEscherichia coli: genes governing the synthesis of glycine betaine and trehalose and their use in metabolic engineering of stress tolerance |
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Authors: | Arne R Strøm |
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Institution: | (1) Department of Biotechnology and UNIGEN Center for Molecular Biology, Norwegian University of Science and Technology, N-7034 Trondheim, Norway |
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Abstract: | Glycine betaine is known to be the preferred osmoprotectant in many bacteria, and glycine betaine accumulation has also been
correlated with increased cold tolerance. Trehalose is often a minor osmoprotectant in bacteria and it is a major determinant
for desiccation tolerance in many so-called anhydrobiotic organisms such as baker's yeast(Saccharomyces cerevisiae). Escherichia coli has two pathways for synthesis of these protective molecules; i.e., a two-step conversion of UDP-glucose and glucose-6-phosphate
to trehalose and a two-step oxidation of externally-supplied choline to glycine betaine. The genes governing the choline-to-glycine
betaine pathway have been studied inE. coli and several other bacteria and higher plants. The genes governing UDP-glucose-dependent trehalose synthesis have been studied
inE. coli andS. cerevisiae. Because of their well-documented function in stress protection, glycine betaine and trehalose have been identified as targets
for metabolic engineering of stress tolerance. Examples of this experimental approach include the expression of theE. coli betA andArthrobacter globiformis codA genes for glycine betaine synthesis in plants and distantly related bacteria, and the expression of theE. coli otsA and yeastTPS1 genes for trehalose synthesis in plants. The published data show that glycine betaine synthesis protects transgenic plants
and phototrophic bacteria against stress caused by salt and cold. Trehalose synthesis has been reported to confer increased
drought tolerance in transgenic plants, but it causes negative side effects which is of concern. Thus, the much-used model
organismE. coli has now become a gene resource for metabolic engineering of stress tolerance. |
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Keywords: | Glycine betaine trehalose betA gene otsA gene codA gene TPS1 gene osmoregulation |
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