The Pseudomonas aeruginosa lectins PA-IL and PA-IIL are controlled by quorum sensing and by RpoS.

In Pseudomonas aeruginosa, many exoproduct virulence determinants are regulated via a hierarchical quorum-sensing cascade involving the transcriptional regulators LasR and RhlR and their cognate activators, N-(3-oxododecanoyl)-L-homoserine lactone (3O-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL). In this paper, we demonstrate that the cytotoxic lectins PA-IL and PA-IIL are regulated via quorum sensing. Using immunoblot analysis, the production of both lectins was found to be directly dependent on the rhl locus while, in a lasR mutant, the onset of lectin synthesis was delayed but not abolished. The PA-IL structural gene, lecA, was cloned and sequenced. Transcript analysis indicated a monocistronic organization with a transcriptional start site 70 bp upstream of the lecA translational start codon. A lux box-type element together with RpoS (sigma(S)) consensus sequences was identified upstream of the putative promoter region. In Escherichia coli, expression of a lecA::lux reporter fusion was activated by RhlR/C4-HSL, but not by LasR/3O-C12-HSL, confirming direct regulation by RhlR/C4-HSL. Similarly, in P. aeruginosa PAO1, the expression of a chromosomal lecA::lux fusion was enhanced but not advanced by the addition of exogenous C4-HSL but not 3O-C12-HSL. Furthermore, mutation of rpoS abolished lectin synthesis in P. aeruginosa, demonstrating that both RpoS and RhlR/C4-HSL are required. Although the C4-HSL-dependent expression of the lecA::lux reporter in E. coli could be inhibited by the presence of 3O-C12-HSL, this did not occur in P. aeruginosa. This suggests that, in the homologous genetic background, 3O-C12-HSL does not function as a posttranslational regulator of the RhlR/C4-HSL-dependent activation of lecA expression.

Identification and characterization of pseudomonas aeruginosa PA-IIL lectin gene and protein compared to PA-IL.

Using the 33 N-terminal amino acids of the fucose/mannose binding lectin PA-IIL of Pseudomonas aeruginosa ATCC 33347 in a tblastn search of P. aeruginos PAOI genomic sequence in GenBank revealed a single open reading frame encoding a 114-amino acid protein (excluding initiator methionine) perfectly matching that amino acid sequence. Following its stop codon there is a GC-rich sequence having a perfect dyad symmetry promoting formation of a hairpin loop structure, potentially enabling rho-independent transcription termination. Upstream of the putative ribosomal binding site there are sequences resembling Vibrio fischeri luxIbox. consistent with autoinduction of this gene, The predicted PA-IIL molecular mass, confirmed by mass spectrometry, is 11,732 Da. Its pI is 3.88. The C-terminal domain is particularly hydrophobic, implying possible embedding in the cell membrane. PA-IIL is similar to P. aeruginosa PA-IL lectin in some amino acids and potential glycosylation sites but lacks cysteine, methionine and histidine. Despite their relations in functions and regulation.,their genes are widely separated (by about 867.5 kb).

'Subinhibitory' erythromycin represses production of Pseudomonas aeruginosa lectins, autoinducer and virulence factors.

Pseudomonas aeruginosa infection is preceded by selective adhesion of the bacteria to the host target cells via diverse adhesins, including lectins. This step enables maximal damage to the target host cells by the bacterially secreted injurious toxins and enzymes. The production of both lectins and many of the virulence factors is positively controlled by transcription activators including signaling autoinducers (N-acyl-L-homoserine lactones). We show in this communication that erythromycin at subminimal growth inhibitory concentrations simultaneously suppresses the production of P. aeruginosa hemagglutinins (including lectins), protease, hemolysin and homoserine lactone autoinducers. The antibiotic-treated bacteria also show reduced virulence to mice, endorsing clinical observations that indicate the efficiency of low-dose erythromycin treatment of persistent drug-resistant P. aeruginosa infections.

Purified Pseudomonas aeruginosa PA-I lectin induces gut growth when orally ingested by rats.

The effects of PA-I lectin isolated from the human pathogen Pseudomonas aeruginosa upon cellular metabolism in vivo have been studied using the rat gut as a model system. Orally ingested PA-I lectin stimulated metabolic activity and induced polyamine accumulation and growth in the small intestine, caecum and colon. The nature and extent of the changes induced by PA-I lectin were similar to those caused by dietary kidney bean lectin and were likely to lead to impaired epithelial cell function and integrity. This finding contributes to our understanding of the possible roles of these lectins in Pseudomonas aeruginosa infection.

Pseudomonas aeruginosa PA-I lectin gene molecular analysis and expression in Escherichia coli.

This communication describes a Pseudomonas aeruginosa DNA fragment (cloned in lambda gt11) which contains the structural gene coding for the galactophilic PA-I lectin (pa-1L, 369 bp) and an additional downstream 237 bp sequence. This DNA is relatively rich in G + C (54%), and exhibits a strong codon preference biased for XXC and also for XXG. The Shine-Dalgarno site of the gene is preceded by an adjacent ATATAT sequence resembling the -10 sequence of the Escherichia coli promoter. The stop codons are followed by a stem and loop structure--typical of the rho-independent transcriptional stop element. This lambda gt11-cloned DNA was expressed in E. coli Y1090 cells. The resulting cell lysates exhibited a galactose-specific hemagglutination and a protein with electrophoretic mobility similar to that of the native PA-I, which were both absent from E. coli lysates infected with ovalbumin gene-bearing bacteriophages. The recombinant PA-I, purified by gel filtration and affinity chromatography, was shown to be a galactophilic hemagglutinin resembling the native lectin in molecular weight and selective reactivity with rabbit anti native PA-I serum. These results are important for development of a safe Pseudomonas aeruginosa vaccine using recombinant DNA techniques, thus avoiding contamination with toxic products of this bacterium.

Analysis of the amino acid sequence of the Pseudomonas aeruginosa galactophilic PA-I lectin.

Based on the NH2-terminal 30-amino acid sequence of Pseudomonas aeruginosa galactophilic PA-I lectin, two degenerate primer oligonucleotides were synthesized and used in polymerase chain reaction with the bacterial chromosomal DNA as a template. A predominant DNA fragment of the appropriate size was radiolabeled and used as a probe for screening a P. aeruginosa genomic lambda gt11 library. One positive clone carrying an insert of about 630 base pairs encompassing the entire PA-I lectin gene was isolated and found to contain a 369-base pair open reading frame between an initiation codon (19 base pairs downstream from the insertion site, subsequent to a Shine-Dalgarno sequence) and two consecutive stop codons, followed by an oligo (seven) A sequence, in a partial dyad symmetry. The deduced amino acid sequence shows excellent agreement with the quantitative amino acid analysis and a perfect match with the NH2-terminal amino acid sequence of the purified lectin. It reveals that the PA-I lectin subunit contains 121 amino acids (M(r) 12,754; pI 4.94) with a predominant central hydrophilic core between two hydrophobic domains. Secondary structure algorithms predict that it is rich in beta sheets and contains several highly antigenic epitopes, but no signal peptide. In the carboxyl region a potential glycosylation site (Asn-Asn-Ser) was identified. Comparative analyses of this lectin sequence with those of lectins from other sources, reported in the protein and gene data banks, did not reveal any extensive homology.