Isolation and characterization of two genes, waaC (rfaC) and waaF (rfaF), involved in Pseudomonas aeruginosa serotype O5 inner-core biosynthesis.

Recent studies have provided evidence to implicate involvement of the core oligosaccharide region of Pseudomonas aeruginosa lipopolysaccharide (LPS) in adherence to host tissues. To better understand the role played by LPS in the virulence of this organism, the aim of the present study was to clone and characterize genes involved in core biosynthesis. The inner-core regions of P. aeruginosa and Salmonella enterica serovar Typhimurium are structurally very similar; both contain two main chain residues of heptose linked to lipid A-Kdo2 (Kdo is 3-deoxy-D-manno-octulosonic acid). By electrotransforming a P. aeruginosa PAO1 library into Salmonella waaC and waaF (formerly known as rfaC and rfaF, respectively) mutants, we were able to isolate the homologous heptosyltransferase I and II genes of P. aeruginosa. Two plasmids, pCOREc1 and pCOREc2, which restored smooth LPS production in the waaC mutant, were isolated. Similarly, plasmid pCOREf1 was able to complement the Salmonella waaF mutant. Sequence analysis of the DNA insert of pCOREc2 revealed one open reading frame (ORF) which could code for a protein of 39.8 kDa. The amino acid sequence of the deduced protein exhibited 53% identity with the sequence of the WaaC protein of S. enterica serovar Typhimurium. pCOREf1 contained one ORF capable of encoding a 38.4-kDa protein. The sequence of the predicted protein was 49% identical to the sequence of the Salmonella WaaF protein. Protein expression by the Maxicell system confirmed that a 40-kDa protein was encoded by pCOREc2 and a 38-kDa protein was encoded by pCOREf1. Pulsed-field gel electrophoresis was used to determine the map locations of the cloned waaC and waaF genes, which were found to lie between 0.9 and 6.6 min on the PAO1 chromosome. Using a gene-replacement strategy, we attempted to generate P. aeruginosa waaC and waaF null mutants. Despite multiple attempts to isolate true knockout mutants, all transconjugants were identified as merodiploids.     

3-hydroxy-3-methylglutaryl coenzyme A reductase of Sulfolobus solfataricus: DNA sequence, phylogeny, expression in Escherichia coli of the hmgA gene, and purification and kinetic characterization of the gene product.

The gene (hmgA) for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34) from the thermophilic archaeon Sulfolobus solfataricus P2 was cloned and sequenced. S. solfataricus HMG-CoA reductase exhibited a high degree of sequence identity (47%) to the HMG-CoA reductase of the halophilic archaeon Haloferax volcanii. Phylogenetic analyses of HMG-CoA reductase protein sequences suggested that the two archaeal genes are distant homologs of eukaryotic genes. The only known bacterial HMG-CoA reductase, a strictly biodegradative enzyme from Pseudomonas mevalonii, is highly diverged from archaeal and eukaryotic HMG-CoA reductases. The S. solfataricus hmgA gene encodes a true biosynthetic HMG-CoA reductase. Expression of hmgA in Escherichia coli generated a protein that both converted HMG-CoA to mevalonate and cross-reacted with antibodies raised against rat liver HMG-CoA reductase. S. solfataricus HMG-CoA reductase was purified in 40% yield to a specific activity of 17.5 microU per mg at 50 degrees C by a sequence of steps that included heat treatment, ion-exchange chromatography, hydrophobic interaction chromatography, and affinity chromatography. The final product was homogeneous, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The substrate was (S)- not (R)-HMG-CoA; the reductant was NADPH not NADH. The Km values for HMG-CoA (17 microM) and NADPH (23 microM) were similar in magnitude to those of other biosynthetic HMG-CoA reductases. Unlike other HMG-CoA reductases, the enzyme was stable at 90 degrees C and was optimally active at pH 5.5 and 85 degrees C.     

Pseudomonas aeruginosa B-band O-antigen chain length is modulated by Wzz (Ro1).

The wbp gene cluster, encoding the B-band lipopolysaccharide O antigen of Pseudomonas aeruginosa serotype O5 strain PAO1, was previously shown to contain a wzy (rfc) gene encoding the O-antigen polymerase. This study describes the molecular characterization of the corresponding wzz (rol) gene, responsible for modulating O-antigen chain length. P. aeruginosa O5 Wzz has 19 to 20% amino acid identity with Wzz of Escherichia coli, Salmonella enterica, and Shigella flexneri. Knockout mutations of the wzz gene in serotypes O5 and O16 (which has an O antigen structurally related to that of O5) yielded mutants expressing O antigens with a distribution of chain lengths differing markedly from that of the parent strains. Unlike enteric wzz mutants, the P. aeruginosa wzz mutants continued to display some chain length modulation. The P. aeruginosa O5 wzz gene complemented both O5 and O16 wzz mutants as well as an E. coli wzz mutant. Coexpression of E. coli and P. aeruginosa wzz genes in a rough strain of E. coli carrying the P. aeruginosa wbp cluster resulted in the expression of two populations of O-antigen chain lengths. Sequence analysis of the region upstream of wzz led to identification of the genes rpsA and himD, encoding 30S ribosomal subunit protein S1 and integration host factor, respectively. This finding places rpsA and himD adjacent to wzz and the wbp cluster at 37 min on the PAO1 chromosomal map and completes the delineation of the O5 serogroup-specific region of the wbp cluster.     

Identification and functional characterization of an ABC transport system involved in polysaccharide export of A-band lipopolysaccharide in Pseudomonas aeruginosa.

Pseudomonas aeruginosa coexpresses two distinct lipopolysaccharide (LPS) molecules known as A band and B band. B band is the serospecific LPS, while A band is the common LPS antigen composed of a D-rhamnose O-polysaccharide region. An operon containing eight genes responsible for A-band polysaccharide biosynthesis and export has recently been identified and characterized (H. L. Rocchetta, L. L. Burrows, J. C. Pacan, and J. S. Lam, unpublished data; H. L. Rocchetta, J. C. Pacan, and J. S. Lam, unpublished data). In this study, we report the characterization of two genes within the cluster, designated wzm and wzt. The Wzm and Wzt proteins have predicted sizes of 29.5 and 47.2 kDa, respectively, and are homologous to a number of proteins that comprise ABC (ATP-binding cassette) transport systems. Wzm is an integral membrane protein with six potential membrane-spanning domains, while Wzt is an ATP-binding protein containing a highly conserved ATP-binding motif. Chromosomal wzm and wzt mutants were generated by using a gene replacement strategy in P. aeruginosa PAO1 (serotype 05). Western blot analysis and immunoelectron microscopy using A-band- and B-band-specific monoclonal antibodies demonstrated that the wzm and wzt mutants were able to synthesize A-band polysaccharide, although transport of the polymer to the cell surface was inhibited. The inability of the polymer to cross the inner membrane resulted in the accumulation of cytoplasmic A-band polysaccharide. This A-band polysaccharide is likely linked to a carrier lipid molecule with a phenol-labile linkage. Chromosomal mutations in wzm and wzt were found to have no effect on B-band LPS synthesis. Rather, immunoelectron microscopy revealed that the presence of A-band LPS may influence the arrangement of B-band LPS on the cell surface. These results demonstrate that A-band and B-band O-antigen assembly processes follow two distinct pathways, with the former requiring an ABC transport system for cell surface expression.     

Targeted disruption of the TGA3 locus in Arabidopsis thaliana

A major drawback to study gene functions in plant systems is the lack of an effective gene knockout strategy. With a large number of plant genes isolated and the accelerating pace by which this collection is growing, the need for their functional analyses at the whole plant level has become increasingly urgent. Here evidence is reported for the first successful disruption of a non-selectable gene in Arabidopsis thaliana by creating a mutant of the TGA3 locus via targeted insertion of the bacterial neo gene conferring kanamycin (Km) resistance. A β-glucuronidase (GUS) expression unit outside the region of homology was used as a screenable marker to distinguish homologous recombination events from those of ectopic insertions. PCR amplification coupled with Southern blot screening identified two putative homologous recombination events among 2580 Km^r calli. One callus line was subsequently isolated and the structure of the targeted TGA3 allele confirmed by Southern blot analyses. This study demonstrates the feasibility of targeting a non-selectable locus in Arabidopsis. Combined with future improvements in negative selection strategies and efficient, transformation methodologies, gene replacement studies in plants could become a routine technique.     

Structural study of circulating thymic factor: a peptide isolated from pig serum. I. Isolation and purification.

A circulating thymic factor (FTS) has been characterized by a bioassay based on its ability to render theta-negative rosette-forming cells theta-positive and azathioprine-sensitive. FTS was sequentially purified and finally isolated from 1000 liters of pig serum by ultrafiltration, gel filtration, and ion exchange chromatography. Its amino acid composition and apparent molecular weight estimated by Sephadex G-25 chromatography, indicate that FTS is a nonapeptide of composition lysine, aspartic acid (or asparagine), serine 2, glutamic acid (or glutamine) 2, glycine 2, and alanine.     

Use of Adenosine 5′-Triphosphate as an Indicator of the Microbiota Biomass in Rumen Contents

A number of techniques were tested for their efficiency in extracting adenosine 5′-triphosphate (ATP) from strained rumen fluid (SRF). Extraction with 0.6 N H₂SO₄, using a modification of the procedure described by Lee et al. (1971), was the most efficient and was better suited for extracting particulate samples. Neutralized extracts could not be stored frozen before assaying for ATP because large losses were incurred. The inclusion of internal standards was necessary to correct for incomplete recovery of ATP. The ATP concentration in rumen contents from a cow receiving a ration of dried roughage (mainly alfalfa hay) ranged from 31 to 56 μg of ATP per g of contents. Approximately 75% of the ATP was associated with the particulate material. The ATP was primarily of microbial origin, since only traces of ATP were present in the feed and none was found in “cell-free” rumen fluid. Fractionation of the bacterial and protozoal populations in SRF resulted in the isolation of an enriched protozoal fraction with a 10-fold higher ATP concentration than that of the separated rumen bacteria. The ATP pool sizes of nine functionally important rumen bacteria during the exponential phase of growth ranged from 1.1 to 17.6 μg of ATP per mg of dry weight. This information indicates that using ATP as a measure of microbial biomass in rumen contents must be done with caution because of possible variations in the efficiency of extraction of ATP from rumen contents and differences in the concentration of ATP in rumen microbes.