The production of labeled betaine by incubation of osmolyte-freePseudomonas aeruginosa with radioactive choline

Preparation and biophysical characterization of recombinant Pseudomonas aeruginosa phosphorylcholine phosphatase

Pseudomonas aeruginosa infections constitute a widespread health problem with high economical and social impact, and the phosphorylcholine phosphatase (PchP) of this bacterium is a potential target for antimicrobial treatment. However, drug design requires high-resolution structural information and detailed biophysical knowledge not available for PchP. An obstacle in the study of PchP is that current methods for its expression and purification are suboptimal and allowed only a preliminary kinetic characterization of the enzyme. Herein, we describe a new procedure for the efficient preparation of recombinant PchP overexpressed in Escherichia coli. The enzyme is purified from urea solubilized inclusion bodies and refolded by dialysis. The product of PchP refolding is a mixture of native PchP and a kinetically-trapped, alternatively-folded aggregate that is very slowly converted into the native state. The properly folded and fully active enzyme is isolated from the refolding mixture by size-exclusion chromatography. PchP prepared by the new procedure was subjected to chemical and biophysical characterization, and its basic optical, hydrodynamic, metal-binding, and catalytic properties are reported. The unfolding of the enzyme was also investigated, and its thermal stability was determined. The obtained information should help to compare PchP with other phosphatases and to obtain a better understanding of its catalytic mechanism. In addition, preliminary trials showed that PchP prepared by the new protocol is suitable for crystallization, opening the way for high-resolution studies of the enzyme structure.

Glycine betaine transmethylase mutant of Pseudomonas aeruginosa

The gene for glycine betaine transmethylase (gbt) was identified in Pseudomonas aeruginosa strain Fildes III by biochemical, physiological, and molecular approaches. Based on sequence analysis, the knockout gene corresponded to an open reading frame (ORF) named PA3082 in the genome of P. aeruginosa PAO1. The translated product of this ORF displayed similarity to transferases of different microorganisms. Mutation in gbt blocked the utilization of choline and glycine betaine as carbon and nitrogen sources.

Constitutive choline transport in Pseudomonas aeruginosa

Pseudomonas aeruginosa has a choline uptake system which is expressed in bacteria grown in the presence of succinate and ammonium chloride as the carbon and nitrogen source, respectively. This system obeys Michaelis-Menten kinetics with an apparent Km value of 53 microM; its activity is not inhibited by high osmolarities in the medium but is partially inhibited by choline metabolites such as betaine and dimethylglycine.

Carbons from choline present in the phospholipids of Pseudomonas aeruginosa

The phospholipid composition of Pseudomonas aeruginosa grown in a mineral medium with choline as the carbon source was: phosphatidylethanolamine, 71.6 +/- 1.4%; phosphatidylglycerol, 11.8 +/- 0.4%; diphosphatidylglycerol, 0.8 +/- 0.4%; phosphatidic acid, 2.4 +/- 0.6%; lysophosphatidylethanolamine, 1.6 +/- 0.3%; phosphatidylcholine 7.9 +/- 0.3%; lysophosphatidylcholine, 3.9 +/- 0.7%. The molar ratio between the acidic and the neutral phospholipids was 0.18. Radiolabeling experiments with [methyl-14C]choline or [1,2-14C]choline carried out in cell suspension from bacteria that were grown in the presence of choline as the sole carbon source demonstrated that the carbons of the N-methyl groups of choline contributed to the synthesis of fatty acids while the carbons comprising the backbone of choline were used for the synthesis of glycerol.

Carnitine resembles choline in the induction of cholinesterase, acid phosphatase, and phospholipase C and in its action as an osmoprotectant in Pseudomonas aeruginosa

The present study demonstrates that under conditions of iso or hyperosmolarity, P. aeruginosa utilized carnitine as the carbon, nitrogen or carbon and nitrogen sources. As occurred in the case of choline, the bacteria synthesized cholinesterase (ChE), acid phosphatase (Ac.Pase) and phospholipase C (PLC) under any of these conditions and in the presence of high or low Pi concentrations. Carnitine acted as an osmoprotectant when the cells were grown in the presence of preferred carbon and nitrogen sources and high NaCl concentrations. Under these conditions the three enzyme activities were not produced. The osmotically stressed bacteria grown under any of the above conditions accumulated betaine. Its presence indicated that carnitine may be metabolized by P. aeruginosa to produce betaine which could account for the induction of the three enzyme activities or its action as an osmoprotectant. The phosphatidylcholine encountered in the host cell membranes allows the bacteria to obtain free choline by the coordinated action of PLC and Ac.Pase. Since the consequence of this action may be cell disruption, the increase of free carnitine in the natural environment of the bacteria is also possible. These two compounds, choline and carnitine, acting in conjunction or separately, may increase the production of PLC and Ac.Pase activities by P. aeruginosa and thus enhance the degradative effect upon the host cells.