Xylan utilization regulon in Xanthomonas citri pv. citri Strain 306: gene expression and utilization of oligoxylosides

Xanthomonas citri pv. citri strain 306 (Xcc306), a causative agent of citrus canker, produces endoxylanases that catalyze the depolymerization of cell wall-associated xylans. In the sequenced genomes of all plant-pathogenic xanthomonads, genes encoding xylanolytic enzymes are clustered in three adjacent operons. In Xcc306, these consecutive operons contain genes encoding the glycoside hydrolase family 10 (GH10) endoxylanases Xyn10A and Xyn10C, the agu67 gene, encoding a GH67 α-glucuronidase (Agu67), the xyn43E gene, encoding a putative GH43 α-l-arabinofuranosidase, and the xyn43F gene, encoding a putative β-xylosidase. Recombinant Xyn10A and Xyn10C convert polymeric 4-O-methylglucuronoxylan (MeGXn) to oligoxylosides methylglucuronoxylotriose (MeGX3), xylotriose (X3), and xylobiose (X2). Xcc306 completely utilizes MeGXn predigested with Xyn10A or Xyn10C but shows little utilization of MeGXn. Xcc306 with a deletion in the gene encoding α-glucuronidase (Xcc306 Δagu67) will not utilize MeGX3 for growth, demonstrating the role of Agu67 in the complete utilization of GH10-digested MeGXn. Preferential growth on oligoxylosides compared to growth on polymeric MeGXn indicates that GH10 xylanases, either secreted by Xcc306 in planta or produced by the plant host, generate oligoxylosides that are processed by Xyn10 xylanases and Agu67 residing in the periplasm. Coordinate induction by oligoxylosides of xyn10, agu67, cirA, the tonB receptor, and other genes within these three operons indicates that they constitute a regulon that is responsive to the oligoxylosides generated by the action of Xcc306 GH10 xylanases on MeGXn. The combined expression of genes in this regulon may allow scavenging of oligoxylosides derived from cell wall deconstruction, thereby contributing to the tissue colonization and/or survival of Xcc306 and, ultimately, to plant disease.

'Candidatus Pasteuria aldrichii', an obligate endoparasite of the bacterivorous nematode Bursilla

A novel bacterium of the genus Pasteuria was discovered parasitizing bacterivorous nematodes of the genus Bursilla, in selected bermudagrass (Cynodon) field plots in Davie, FL, USA. Soil containing this bacterium was sampled and supplied with bi-weekly inoculations of cultured species of the genus Bursilla in order to build and maintain a source of endospores for continuous in vivo conservation of the bacteria for further study and characterization. 16S rRNA gene sequence similarities supported its congeneric ranking with other members of the genus Pasteuria that have been identified from nematodes and cladocerans. There were, however, no clear sister candidates for this organism, which supported the evidence of endospore ultrastructure and host-range studies, suggesting it belonged to a novel taxon. Because members of the genus Pasteuria cannot yet be isolated, definitive type strains could not be maintained; therefore, the name 'Candidatus Pasteuria aldrichii' is proposed for this organism.

Airway neutrophilia in COPD is not associated with increased neutrophil survival

Neutrophilic airway inflammation is a prominent feature of chronic obstructive pulmonary disease (COPD) and correlates with disease severity. The mechanisms that determine the extent of neutrophilia could involve increased influx or prolonged survival of neutrophils. The aim of the study was to assess whether neutrophil pro-survival mechanisms are increased in the airways of subjects with COPD owing to the presence of anti-apoptotic factors in the bronchial lining fluid. Induced sputum samples were collected from 20 subjects with stable COPD, 14 healthy smokers and 14 healthy controls. Quantification of apoptotic neutrophils was based on typical morphological cell changes. Anti-apoptotic, pro-survival activity in the sputum was studied by culturing peripheral blood neutrophils with the fluid phase of induced sputum. Apoptosis was assessed both by morphology and flow cytometry using Annexin V/7-aminoactinomycin D staining. COPD patients and healthy smokers had significantly higher percentages of sputum neutrophils than healthy controls. However, there were no significant differences between the three subject groups in either the proportion of apoptotic neutrophils in sputum or the in vitro anti-apoptotic activity detected in the sputum fluid phase. In conclusion, prolonged survival of neutrophils in sputum is not a feature of chronic obstructive pulmonary disease and cannot explain the increased numbers of airway neutrophils in this disease.

Pasteuria spp.: Systematics and Phylogeny of These Bacterial Parasites of Phytopathogenic Nematodes

Pasteuria spp. include endospore-forming bacterial pathogens of cladoceran crustaceans and plant-parasitic nematodes. Propagation of these nematode pathogens requires attachment of soilborne endospores to nematode hosts, infection, growth, sporulation, and release of endospores to repeat the cycle of infection and propagation. The ability of these bacteria to suppress the levels of plant-parasitic nematodes in the field has made them particularly promising candidates for biocontrol of nematode diseases of plants. Genes encoding 16S ribosomal RNA have been sequenced for the cladoceran (water flea) parasite and type species, Pasteuria ramosa, and for Pasteuria spp. isolated from root-knot (Meloidogyne arenaria race 1 and Meloidogyne sp.), soybean cyst (Heterodera glycines), and sting (Belonolaimus longicaudatus) nematodes. These have provided a phylogenetic basis for their designation to a distinct clade within the family Alicyclobacillaceae of the gram-positive endospore-forming bacteria. Two apparent biotypes of P. penetrans demonstrating a host preference for different Meloidogyne spp. showed identical 16S rDNA sequences, suggesting host-recognition evolves within a given species. The sequences of genes encoding sporulation transcription factors, sigE and sigF, from P. penetrans biotype P-20 show different phylogenetic relationships to other endospore-forming bacteria, supporting their application to further discriminate Pasteuria spp. and biotypes. Distribution of an adhesin-associated epitope on polypeptides from different Pasteuria isolates provides an immunochemical approach to differentiate species and biotypes with specific host preferences. Application of bioinformatics to genomic data, as well as further characterization of the biochemical basis for host recognition, will facilitate development of Pasteuria spp. as benign alternatives to chemical nematicides.

Molecular cloning of a teleost growth hormone receptor and its functional interaction with human growth hormone

This paper reports the first full-length cDNA sequence of a growth hormone receptor (GHR) from a teleost fish and its functional expression in cultured eukaryotic cells. The cDNA sequence, from Carassius auratus (goldfish), encodes a protein of 602 amino acids (aa) akin in architecture to the GHRs of other species. Despite the presence of motifs characteristic of GHR, the overall homology between the goldfish GHR and other GHRs is very low ( approximately 40% aa identity). CHO cells transfected with this receptor cDNA can be stimulated to proliferate by human growth hormone (hGH). In addition, the transfected cells can transactivate a co-expressed mammalian serine protease inhibitor (Spi) 2.1 promoter upon stimulation by hGH, indicating the successful interaction of the fish receptor with the mammalian ligand to evoke the down-stream post-receptor events. Tissue distribution studies indicated that the receptor is mostly expressed in the liver and hypothalamus of goldfish. A single mRNA transcript of a size of about 4 kb was found in the goldfish liver.

Characterization of the ecdysteroid UDP-glucosyltransferase gene of Spodoptera litura multinucleocapsid nucleopolyhedrovirus

The ecdysteroid UDP-glucosyltransferase (EGT) gene of Spodoptera litura multinucleocapsid nucleopolyhedrovirus (SpltMNPV), Guangzhouisolate was sequenced. The open reading frame of the gene is 1530 nucleotides long, encoding a putative protein of 509 amino acids with Mr of 58,500. The 5' noncoding region has a TATA box. A polyadenylation signal, AATAAA, is contained downstream of the translation stop codon. A putative signal peptide is present at the N-terminus of the protein. Homology comparison with other baculovirus egt genes showed that these genes are highly conserved. The SpltMNPV egt gene is closely related to that of Spodoptera littoralis nucleopolyhedrovirus (SliNPV) with the identities of 84% in nucleotide and 91% in amino acid, respectively. In this study, an alignment of amino acid sequences has been made and a tentative phylogenetic tree of twelve baculovirus egts is presented.

[The identification of BmNPV gp64 envelope gene]

gp64 glycoprotein, an abundant and the only membrane glycoprotein encoded by the baculovirus genome, contains a signal peptide sequence at N-terminus, a transmembrane anchor at c-terminus and a ectodomain between them. The efficient signal sequences and the transmembrane anchor sequences of AcMNPV gp64 gene have been exploited in baculovirus expression system. Using 1.3 kb AcMNPV gp64 gene coding sequence as the probe, the nucleotide sequence of BmNPV gp64 gene was determined, and a 1530 nucleotide open reading frame flanked by an AT-rich sequence was identified that could encode a polypeptide with 509 amino acid residues. Computer analysis indicated BmNPV gp64 gene is 84.3% identical to AcMNPV at the level of nucleotide sequence and 94.7% identical at the level of predicted amino acid sequence.

[Cloning and analysis of the regulatory gene fragment induced with seed extract in Rhizobium huakuii strain 7653R]

The large plasmids of strain 7653R were digested with restriction enzyme EcoRI. Their DNA fragments were cloned into the expression vector pMP220 to construct a lacZ fusion pool, which were transferred into the recipient strain 7653R. Tri-transconjugants were selected onto plates containing X-gal and seed extract. Five blue colonies were assayed of their beta-galactosidase activity after incubation with or without seed extract. A positive induced strain HN18 was obtained. Hybridization of nodDABC probe on the recombinant plasmid pHN18 showed a 1.7 kb positive band. The evidence makes a deduction that the pHN18 contains a promoter of nod operon.