Abstract
An amount of human pro-apoptotic Bax as low as 0.01% of total protein was sufficient to cause cell death in Escherichia coli. The bacterial cell death was examined using a viable bacteria-specific fluorescence indicator system and loss of colony formation ability. Co-expression of anti-apoptotic Bcl-xL showed a modest inhibitory effect on the cell death caused by Bax. The trace amount of Bax elongated E. coli and accumulated monounsaturated fatty acids, suggesting an unusual metabolism of redox in the host. In fact, an increase of KCN-dependent O2 consumption accompanied the expression of Bax. At the same time, a fluorescent pH indicator showed the apparent accumulation of protons outside the cell, suggesting that the membrane is intact. Bax increased the level of superoxide anion as measured by the expression of superoxide-dependent promoter. Nicked DNA was significantly generated, and the frequency of mutations resistant to rifampicin was increased by 30-fold, depending upon the expression of Bax. It is proposed that trace amounts of Bax increase oxygen consumption, triggering generation of superoxide, which affects DNA, leading to bacterial death.
Highlights
Apoptosis in multicellular organisms is an active cellular self-destruction that is directed by genes
We found that an Escherichia coli cell transformed with a prokaryote expression vector carrying mammalian bax or bak cDNAs grew poorly in solid and liquid media
When this cDNA was introduced into mammalian cell FDC-P1, this version of Bax accelerated apoptosis induced by interleukin-3 withdrawal [22]
Summary
Apoptosis in multicellular organisms is an active cellular self-destruction that is directed by genes. Co-expression of anti-apoptotic proteins Bcl-2, Bcl-xL, or Mcl-1 abolished the cytotoxicity of Bax or Bak in yeast cells [13, 16, 18, 19]. Inducible expression of Bax in mammalian Jurkat T cells initiated apoptosis without an extra death stimulus [20] This process accompanied the generation of reactive oxygen species (ROS), and decrease of mitochondrial membrane potential [20]. To biochemically investigate the function(s) of Bax in detail, we have chosen this organism as a Bax-expressing host, because there is no report that E. coli has endogenous bcl-2-related genes for interaction with Bax. Here, we present that a trace expression of Bax kills E. coli cells and that this process includes many physiological changes with regard to monounsaturated fatty acid composition, dioxygen consumption, generation of reactive oxygen species, and nicked DNA
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