The Potassium-Uptake Systems, Trk and Kdp, Coordinately Contribute to Growth Regulation and Survival of M. tuberculosis in Ion-Depleted and Acidic Environments

The Mycobacterium tuberculosis bacterium encodes two active potassium (K+)-uptake transport systems, the Trk and the Kdp. The Trk is the low-affinity K+ transporter, consisting of two TrkA proteins, while the Kdp consists of the high-affinity K+ transporter KdpFABC and the two-component system KdpDE. Both transporters are utilised by the bacteria for growth and survival. During growth, the bacteria utilise the constitutively expressed Trk and suppress the Kdp, but upregulate both transporters during survival. In the current study, we investigated the interactive effects of these systems on bacterial growth and survival. This was achieved by first constructing a M. tuberculosis mutant strain in which both the Trk and Kdp systems were inactivated by homologous recombination. The mutant was evaluated for its growth kinetics in planktonic cultures, as well as survival in biofilm and macrophage cultures. The constructed M. tuberculosis mutant showed faster growth rates in planktonic cultures, but was attenuated for both biofilm formation and intracellular survival in isolated human monocyte-derived macrophages. These results illustrate that both K+-uptake systems are essential to sustain slow rates of bacterial growth, as well as for bacterial persistence in hostile environments via optimisation of biofilm formation, and intracellular survival in macrophages. (Words: 194)