Glycerol andl-α-Glycerol-3-phosphate uptake bypseudomonas aeruginosa

Transport of glycerol by Pediococcus pentosaceus isolated from wine

Pediococcus pentosaceus N(5)p is a strain isolated from wine that uses glycerol as its sole carbon source, mainly via the glycerol kinase pathway. The transport of glycerol was investigated in resting cells of this strain. Glycerol uptake followed a Michaelis-Menten relationship with an observed apparent K(m) of 33 microM and a V(max) of 2.5 nmol/min/mg of cell protein. The transport system was specific for glycerol, which was present in the cells grown either on glycerol or glucose suggesting its constitutive nature. The presence of uptake when resting cells were treated with HgCl(2) and the absence of counterflow indicate that facilitated diffusion is not involved in glycerol transport. On the other hand, glycerol uptake was inhibited by the metabolic poisons that affect ATP availability by acting on either electron transport or ATPase activity, and by the proton-conducting uncouplers without any effect on glycerol kinase activity. The restoration of glycerol uptake in de-energized cells by the addition of glucose and low concentration of cyanide-m-chlorophenyl hydrazone was achieved. These results, the first in the genus Pediococcus, provide evidence for an energy-dependent uptake of glycerol that involves the proton motive force directly or coupled with ATP synthesis.

Structure and gene-polypeptide relationships of the region encoding glycerol diffusion facilitator (glpF) and glycerol kinase (glpK) of Pseudomonas aeruginosa

The glycerol facilitator is one of the few known examples of bacterial solute transport proteins that catalyse facilitated diffusion across the cytoplasmic membrane. A second protein, glycerol kinase, is involved in entry of external glycerol into cellular metabolism by trapping glycerol in the cytoplasm as sn-glycerol 3-phosphate. Evidence is presented that glycerol transport in Pseudomonas aeruginosa is mediated by a similar transport system. The genes encoding the glycerol facilitator, glpF, and glycerol kinase, glpK, were isolated on a 4.5 kb EcoRI fragment from a chromosomal mini-library by functional complementation of an Escherichia coli glpK mutant after establishing a map of the chromosomal glpFK region with the help of a PCR-amplified glpK segment. The nucleotide sequence revealed that glpF is the promoter-proximal gene of the glpFK operon. The glycerol facilitator and glycerol kinase were identified in a T7 expression system as proteins with apparent molecular masses of 25 and 56 kDa, respectively. The identities of the glycerol facilitator and glycerol kinase amino acid sequences with their counterparts from Escherichia coli were 70 and 81%, respectively; this similarity extended to two homologues in the genome sequence of Haemophilus influenzae. A chromosomal delta glpFK mutant was isolated by gene replacement. This mutant no longer transported glycerol and could no longer utilize it as sole carbon and energy source. Two ORFs, orfX and orfY, encoding a putative regulatory protein and a carbohydrate kinase of unknown function, were located upstream of the glpFK operon.

Regulation of glycerol metabolism in Pseudomonas aeruginosa: characterization of the glpR repressor gene

The operons of the glp regulon encoding the glycerol metabolic enzymes of Pseudomonas aeruginosa were hitherto believed to be positively regulated by the product of the glpR regulatory gene. During nucleotide sequence analysis of the region located upstream of the previously characterized glpD gene, encoding sn-glycerol-3-phosphate dehydrogenase, an open reading frame (glpR) was identified which encodes a protein of 251 amino acids that is 59% identical to the Glp repressor from Escherichia coli and could be expressed as a 28-kDa protein in a T7 expression system. Inactivation of chromosomal glpR by gene replacement resulted in constitutive expression of glycerol transport activity and glpD activity. These activities were strongly repressed after introduction of a multicopy plasmid containing the glpR gene; the same plasmid also efficiently repressed expression of a glpT-lacZ+ transcriptional fusion in an E. coli glpR mutant. Analysis of the glpD and glpF upstream region identified conserved palindromic sequences which were 70% identical to the E. coli glp operator consensus sequence. The results suggest that the operons of the glp regulon in P. aeruginosa are negatively regulated by the action of a glp repressor.

Identification of Pseudomonas aeruginosa glpM, whose gene product is required for efficient alginate biosynthesis from various carbon sources

In a mucB (algN) genetic background, insertion of an omega element approximately 200 bp downstream of glpD, encoding sn-glycerol-3-phosphate dehydrogenase from Pseudomonas aeruginosa, had an adverse effect on alginate biosynthesis from various carbon sources. The insertion inactivated glpM, a gene encoding a 12,040-M(r) hydrophobic protein containing 109 amino acids. This protein, which was expressed in a T7 RNA polymerase expression system, appears to be a cytoplasmic membrane protein.

Cloning and nucleotide sequence of the glpD gene encoding sn-glycerol-3-phosphate dehydrogenase of Pseudomonas aeruginosa

Nitrosoguanidine-induced Pseudomonas aeruginosa mutants which were unable to utilize glycerol as a carbon source were isolated. By utilizing PAO104, a mutant defective in glycerol transport and sn-glycerol-3-phosphate dehydrogenase (glpD), the glpD gene was cloned by a phage mini-D3112-based in vivo cloning method. The cloned gene was able to complement an Escherichia coli glpD mutant. Restriction analysis and recloning of DNA fragments located the glpD gene to a 1.6-kb EcoRI-SphI DNA fragment. In E. coli, a single 56,000-Da protein was expressed from the cloned DNA fragments. An in-frame glpD'-'lacZ translational fusion was isolated and used to determine the reading frame of glpD by sequencing across the fusion junction. The nucleotide sequence of a 1,792-bp fragment containing the glpD region was determined. The glpD gene encodes a protein containing 510 amino acids and with a predicted molecular weight of 56,150. Compared with the aerobic sn-glycerol-3-phosphate dehydrogenase from E. coli, P. aeruginosa GlpD is 56% identical and 69% similar. A similar comparison with GlpD from Bacillus subtilis reveals 21% identity and 40% similarity. A flavin-binding domain near the amino terminus which shared the consensus sequence reported for other bacterial flavoproteins was identified.

The agmR gene, an environmentally responsive gene, complements defective glpR, which encodes the putative activator for glycerol metabolism in Pseudomonas aeruginosa

The genes for the peripheral glycerol carbon metabolic pathway (glp) in Pseudomonas aeruginosa are postulated to be positively regulated by GlpR. A gene complementing the glpR2 allele, affecting expression of the putative activator, was cloned by a bacteriophage mini-D3112-based in vivo cloning method. Mini-D3112 replicons were isolated by transfecting glpR2 strain PRP406 and selecting clones able to grow on minimal medium containing glycerol as the sole carbon and energy source. Preliminary biochemical characterization indicated that the cloned activator gene for glycerol metabolism (agmR) may not be allelic to glpR. Restriction analysis and recloning of DNA fragments located the agmR gene to a 2.3-kb EcoRV-SstI DNA fragment. In a T7 RNA polymerase expression system, a single 26,000-Da protein was expressed from this DNA fragment. The amino acid sequence of this protein, deduced from the nucleotide sequence reported here, demonstrates its homology to the effector (or regulator) proteins of the environmentally responsive two-component regulators. The carboxy-terminal region of AgmR contains a possible helix-turn-helix DNA-binding motif and resembles sequences found in transcriptional regulators of the LuxR family.

Chromosomal mapping of mutations affecting glycerol and glucose catabolism in Pseudomonas aeruginosa PAO

Mutations causing deficiencies in the inducible, membrane-associated sn-glycerol-3-phosphate dehydrogenase (glpD) and in inducible glucose transport (glcT) were mapped on the Pseudomonas aeruginosa PAO1 chromosome by using the generalized transducing phages F116L and G101. These mutations, in separate catabolic regulatory units, were cotransducible with a previously described cluster of carbohydrate catabolic gene loci (zwf-1 eda-9001 edd-1) that maps at ca. 50 to 53 min on the chromosome. Mutant strain PFB362 (glcT1) did not transport glucose and did not produce a functional, periplasmic, glucose-binding protein that is required for glucose transport. This mutation was cotransducible with zwf-1 (70%), nalA (29%), and phe-2 (19%) but not with glpD1 or leu-10. The glpD1 mutation in strain PRP408 was cotransducible with zwf-1 (5%), eda-9001 (4%), and edd-1 (1%) and also with ami-151 (17%) and phe-2 (33%). These results expand the number of known carbohydrate catabolism genes that are clustered in the 50- to 55-min region of the PAO1 chromosome and allow us to propose the following relative gene order: ami-151 glpD1 phe-2 nalA zwf-1 eda-9001 edd-1 glcT1 leu-10. Three independently obtained nal determinants for high-level resistance to nalidixic acid, which were employed in these studies, exhibited similar cotransduction frequencies with several flanking marker mutations.

Permeability of Pseudomonas aeruginosa outer membrane to hydrophilic solutes

Pseudomonas aeruginosa is usually resistant to a wide variety of antibacterial agents, and it has been inferred, on the basis of indirect evidence, that this was due to the low permeability of its outer membrane. We determined the permeability of P. aeruginosa outer membrane directly, by measuring the rates of hydrolysis of cephacetrile, cephaloridine, and various phosphate esters by hydrolytic enzymes located in the periplasm. The permeability to these compounds was about 100-fold lower than in the outer membrane of Escherichia coli K-12. Also, we found that the apparent Km values for active transport of various carbon and energy source compounds were typically higher than 20 microM in P. aeruginosa, in contrast to E. coli in which the values are usually lower than 5 microM. These results also are consistent with the notion that the P. aeruginosa outer membrane indeed has a low permeability to most hydrophilic compounds and that this membrane acts as a rate limiting step in active transport processes with high Vmax values.