Potassium Transport Mechanisms in Bacterial Systems

Potassium ions are indispensable for bacterial life, contributing to osmotic balance, enzyme activity and maintenance of membrane potential. Bacteria employ multiple transport systems to import K+ across the cytoplasmic membrane, calibrated to prevailing environmental conditions. At low external K+ concentrations, the high‐affinity Kdp‐ATPase system is induced, utilising ATP hydrolysis to drive K+ uptake against steep gradients. Constitutive systems, such as the Trk and Kup uptake pathways, operate under moderate K+ availability, relying on membrane potential and accessory subunits to facilitate ion flow. Under high‐potassium or alkaline stress, specialised transporters like the Ktr channels become active, ensuring continued homeostasis. Regulation occurs at both transcriptional and post‐translational levels, with second messengers such as cyclic di‐adenosine monophosphate (c-di-AMP) modulating transporter activity and abundance in response to osmotic and nutritional cues. Structural studies have revealed the modular architecture of these systems, highlighting conformational changes that underlie gating and ion selectivity. Together, these mechanisms confer resilience to fluctuating environments, underpinning bacterial survival in diverse ecological niches and informing strategies to target pathogenic species.

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Technical terms

Kdp‐ATPase: A high‐affinity, P‐type ATPase complex that pumps K+ into the cytoplasm at low external concentrations through ATP hydrolysis and transient phosphorylation of the KdpB subunit.

Trk system: A constitutive, multisubunit K+ uptake pathway in many bacteria, comprising TrkA regulatory proteins and membrane-embedded TrkH/G transporters that exploit membrane potential for ion movement.

Kup transporter: A secondary K+ import system with lower affinity than Kdp‐ATPase, often regulated by auxiliary domains responding to cellular energy status and ionic milieu.

Ktr channel: A passive or voltage‐gated K+ channel activated under high external K+ or alkaline conditions, contributing to rapid K+ equilibration and osmotic adjustment.

c-di-AMP: Cyclic di-adenosine monophosphate, a bacterial second messenger that binds to regulatory motifs on transport proteins to mediate feedback control of potassium homeostasis.

References

1. Wie Bakterien die Aufnahme von Kaliumionen regulieren. BIOspektrum (2022).
2. K+-transport Protein TrkA of Escherichia coli Is a Peripheral Membrane Protein That Requires other trk Gene Products for Attachment to the Cytoplasmic Membrane*. Journal of Biological Chemistry (1989).
3. Characterization of the Phosphorylated Intermediate of the K+-translocating Kdp-ATPase from Escherichia coli. Journal of Biological Chemistry (1989).