Osmoregulation in <i>Bacillus subtilis</i> under potassium limitation: a new inducible K⁺-stimulated, VO₄^3–-inhibited ATPase

Abstract

Bacillus subtilis exhibited an inducible K+-transporting ATPase activity with apparent Km and maximum velocity Vmax of 12.9 microM and 25.1 micromol x min(-1) x (g cell protein)(-1), respectively, when cultivated on a synthetic medium containing less than 400 microM K+. Due to this enzyme, the growth rate of the bacterium in synthetic medium was not changed down to 115 microM K+, and the bacterium was able to grow down to 20 microM K+. The limiting K+ concentration was higher in media with osmolarity increased by NaCl or sucrose. The ATPase was inhibited by micromolar concentrations of vanadate (Ki = 1.6 microM). The ATPase activity was not stimulated by any other monovalent cation. The subunit of this ATPase, with an Mr of 52000, covalently bound the gamma phosphate group of ATP. This phosphorylated intermediate was unstable in neutral and basic pH as well as in the presence of potassium and was stable in acid pH. The enzyme did not show immunological cross-reactivity with antibody against Kdp ATPase of Escherichia coli.

Rapid Surface Motility in Bacillus subtilis Is Dependent on Extracellular Surfactin and Potassium Ion

“…These results were each scored visually, but the extent of surface biomass was not quantified. The finding of film growth stimulation by such low levels of K ϩ ion may simply represent a threshold for the putative high-affinity K ϩ transporter in B. subtilis (22) or could signify induction of potassium-dependent genes that control colony growth.…”

KtrAB and KtrCD: Two K+Uptake Systems inBacillus subtilisand Their Role in Adaptation to Hypertonicity

“…Mutants with defects in the TetA(L) system show reduced growth in medium containing a low concentration of K ϩ (55). In addition, B. subtilis cells exhibit an inducible K ϩ uptake activity proposed to be associated with a K ϩ -activated P-type ATPase (48). This K ϩ uptake activity is clearly not mediated by a KdpFABC-type K ϩ uptake system (1,21,44), since no kdprelated genes are found in the B. subtilis genome (31).…”

“…Thus, it is apparent that B. subtilis actively modulates its intracellular K ϩ level in response to changes in growth conditions (e.g., increases in osmolality) and to the presence of compatible solutes. It is therefore not surprising that B. subtilis exhibits an increased demand for K ϩ when grown in high-osmolality minimal medium lacking compatible solutes (48).…”

Potassium Transport in a Halophilic Member of theBacteriaDomain: Identification and Characterization of the K+Uptake Systems TrkH and TrkI fromHalomonas elongataDSM 2581T

“…Homologues of Kdp were found in many other Bacteria (9,47). Furthermore, it is now known that P-type ATPases different from Kdp are involved in K ϩ uptake in Bacteria as well (36). The Ktr system consists of two components: a transmembrane-spanning subunit named KtrB, forming the actual pore, and a cytoplasmic membrane-associated KtrA protein containing a NAD ϩ -binding domain.…”