Characterization of two phosphate transport systems in Acinetobacter johnsonii 210A

Abstract

The transport of Pi was characterized in Acinetobacter johnsonii 210A, which is able to accumulate an excessive amount of phosphate as polyphosphate (polyP) under aerobic conditions. P. is taken up against a concentration gradient by energy-dependent, carrier-mediated processes. A. johnsonii 210A, grown under P.limitation, contains two uptake systems with K, values of 0.7 ± 0.2 PuM and 9 ± 1 uM. Pi uptake via the high-affinity component is drastically reduced by NN'-dicyclohexylcarbodiimide, an inhibitor of H+-ATPase, and by osmotic shock. Together with the presence of P,-binding activity in concentrated periplasmic protein fractions, these results suggest that the high-affinity transport system belongs to the group of ATP-driven, binding-protein-dependent transport systems. Induction of this transport system upon transfer of cells grown in the presence of excess Pi to P,-free medium results in a 6-to 10-fold stimulation of the Pi uptake rate. The constitutive low-affinity uptake system for P1 is inhibited by uncouplers and can mediate counterflow of Pi, indicating its reversible, secondary nature. The presence of an inducible high-affinity uptake system for P. and the ability to decrease the free internal P1 pool by forming polyP enable A. johnsonii 210A to reduce the P1 concentration in the aerobic environment to micromolar levels. Under anaerobic conditions, polyP is degraded again and Pi is released via the low-affinity secondary transport system. Enhanced biological phosphorus removal from domestic wastewaters in full-scale activated-sludge plants is currently perceived to hinge on the provision of alternate stages in which the activated sludge is subjected to anaerobic and aerobic conditions (40). A characteristic feature of such plants is that Pi, after being released from the biomass in an anaerobic stage, is reincorporated in the biomass during aeration, together with part or all of the influent Pi (16).

Studies of Cytochrome c Oxidase-Driven H+-Coupled Phosphate Transport Catalyzed by the Saccharomyces cerevisiae Pho84 Permease in Coreconstituted Vesicles

“…At the experimental P i and Mg 2+ , Mn 2+ , and Co 2+ concentrations, 36% (Mg 2+ ), 87% (Mn 2+ ), and 70% (Co 2+ ) of the P i is at pH 7 present as metal-P i complexes in the incubation mixture (22)(23)(24). These observations indicate that P i is transported as MeHPO 4 in symport with H + , in agreement with the phosphate uptake system in Acinetobacter johnsonii (25). When EDTA was added to energized proteoliposomes prior to addition of the divalent cations, phosphate uptake was essentially abolished as in the presence of EDTA alone (not shown).…”

“…Transport was assessed in the absence (2) and in the presence of 2 mM Mn 2+ ([), 2 mM Co 2+ (O), 2 mM Mg 2+ (9), and 0.5 mM EDTA (b). system of A. johnsonii 210A (25), the presence of Mg 2+ exerted an inhibitory effect on phosphate accumulation in reconstituted proteoliposomes as compared to the effects of Mn 2+ and Co 2+ (Figure 4). When the predominance of the MeHPO 4 complex under the experimental conditions used in this study and the influence on the Pho84p transport activity are considered, the obtained results suggest that P i is most likely transported as a MeHPO 4 complex.…”

Inorganic polyphosphate and the induction of rpoS expression

“…Poly(P) accumulates in massive amounts in many bacteria and fungi and in smaller amounts in every microbe, plant, and animal examined (1)(2)(3). Potential functions of poly(P) include the following: (i) a substitute for ATP for sugar and adenylate kinases (4-6), (ii) a phosphate reservoir (1), (iii) a chelator for divalent cations (7,8), (iv) a buffer for alkaline stress (9), (v) a component in competence for DNA entry and transformation (10,11), and (vi) a factor in regulatory responses to stresses and nutritional deficiencies (12).…”

Phosphate concentration regulates transcription of the Acinetobacter polyhydroxyalkanoic acid biosynthetic genes

“…After extension with reverse transcriptase, cDNA products were examined by electrophoresis through an 8% polyacrylamide gel. To map transcriptional start points, sequencing reactions were performed on the corresponding DNA by the dideoxychain method (30), using [␣- 35 S]dATP and a T7 sequencing kit (Pharmacia LKB) with the same primers used for the primer extension reactions.…”

“…Although the phosphate uptake systems in Acinetobacter spp. resemble the two major transport systems of Escherichia coli (35), little is known of these processes at the molecular level. In E. coli, a number of genes in the phosphate (pho) regulon which are involved in the transport and use of phosphate are expressed coordinately when the cell is starved of phosphate (36).…”