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. 2025 Mar;603(5):1325-1328.
doi: 10.1113/JP288355. Epub 2025 Feb 5.

Evolutionary poker lacks a full deck when modelling the LTEE Cit+ phenotype

Scott A Minnich  1 , Carolyn J Hovde  1
Affiliations

Evolutionary poker lacks a full deck when modelling the LTEE Cit+ phenotype

Scott A Minnich et al. J Physiol. 2025 Mar.
No abstract available

Keywords: contingency; escherichia coli Cit+; evolution modeling; long‐term evolution experiment.

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Conflict of interest statement

No competing interests declared.

Figures

Figure 1
Figure 1. E. coli B aerobic citrate utilization requires constitutive expression of CitT and a suppressor mutation of dcuS −
The CitT antiporter (green complex in the inner membrane) is expressed aerobically after citT amplification followed by chromosome remodelling to capture an aerobic promoter. The antiporter function of CitT is depicted as uptake of external citrate (green spheres) and export of a C4‐dicarboxylic acid, such as succinate (red spheres). At this initial stage, import of citrate yields a net gain of two carbons for metabolism. However, as growth continues and succinate accumulates outside the cell, succinate cannot be recaptured. This is because in E. coli B DcuS is defective and cannot phosphorylate DcuR (see X under DcuS) preventing expression of DctA that is required for C4‐dicarboxylate uptake. Overcoming the lack of the DcuSR two‐component system requires a point mutation of the dctA promoter. This took 15 years (33,000 generations) to occur in LTEE and only happened in one of the 12 populations.
Figure 2
Figure 2. E. coli K12 aerobic citrate utilization only requires constitutive expression of CitT.
The CitT antiporter (green complex in the inner membrane) is expressed aerobically after citT amplification followed by chromosome remodelling to capture an aerobic promoter. The antiporter function of CitT is depicted as uptake of external citrate (green spheres) by CitT driven by export of a C4‐dicarboxylic acid, such as succinate (red spheres). As growth continues and succinate accumulates in the environment, it binds to the DcuS sensor protein of the DcuSR two‐component system (purple complex in inner membrane). This binding induces DcuS to auto‐phosphorylate (DcuS∼P) which then phosphorylates DcuR. DcuR∼P transcriptionally activates dctA, coding for a C4‐dicarboxylate transporter. The DctA protein transporter, orange complex in the inner membrane, recaptures the four carbons lost by the CitT antiporter. Imported succinate can feed directly into the citric acid cycle and be fully oxidized to CO2 and H2O.
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