Purification and electron microscopy of a large plasmid of Rhizobium meliloti 41.

A large plasmid DNA molecule was purified from Rhizobium meliloti 41 by CsCl-ethidium bromide density gradient centrifugation. Electron microscopic and agarose gel electrophoretic data suggest that addition of alkali effectively removes the chromosomal DNA, the plasmid DNA can be precipitated from the cleared lysate and no gradient centrifugation is needed for plasmid purification.

Phenotypic reversion of nitrogenase in pleiotropic mutants of Rhizobium meliloti.

In two out of three pleiotropic mutants of Rhizobium meliloti, defective in nitrate reductase induced by amino acid utilization in vegetative bacteria and in symbiotic nitrogen fixation, nitrogenase activity could be restored completely by purines and partially by the amino acids L-glutamate, L-aspartate, L-glutamine, and L-asparagine. The compounds restoring effectiveness in nitrogen fixation did not restore nitrate reductase activity in vegetative bacteria. The restoration of effectiveness supports our earlier conclusion that the mutation is not in the structural gene for a suggested common subunit of nitrogenase and nitrate reductase.

Generalized transduction in Rhizobium meliloti.

The phage 11 of R. meliloti performs generalized transduction. This was confirmed by the variety of single markers transferred and by separating transducing particles containing BUdR-labelled bacterial DNA. The transduction frequencies depended on the marker. Linked alleles were mapped by cotransduction on fragments of bacterial DNA equal in size to the phage DNA. With crosses between antibiotic resistancy and auxotrophic markers a partial map was constructed with str, cml, pur-19, and leu-44 sites. With a few multi-auxotrophic mutants linkage data of conjugation were compared with the linkage by cotransduction.

Transposon Tn917PF1 mutagenesis in Bacillus licheniformis.

The plasmid pTnPFl containing the transposon Tn917PF1 was introduced into the protoplasts of two Bacillus licheniformis strains in the presence of polyethylene glycol. Transpositions were produced at high temperature which inhibited plasmid replication and kanamycin was used for selection.Transposon Tn917PF1 was inserted randomly into the bacterial chromosome,producing different auxotrophic, prophage BLF and bacitracin-non-producing mutants. The auxotrophic mutant phenotypes were characterized by the Holliday-test and some mutations by hybridization with a transposon DNA probe. Insertions for the entire chromosome or for the prophage genophore were found at random, but preferred target sites were detected within limited regions, like the bacitracin synthetase or sulphate reductase genes. The partial physical map of the chromosomal region of bacitracin synthetase was constructed based on the hybridization patterns of insertion mutants.

Isolation of a beta-galactosidase-encoding gene from Bacillus licheniformis: purification and characterization of the recombinant enzyme expressed in Escherichia coli.

The Bacillus licheniformis beta-galactosidase gene, lacBl, was cloned on a 5.8-kb HindIII fragment into pBR322 and expressed by its own promoter in Escherichia coli. Deletion and complementation analysis showed that the enzyme-encoding region was located on a 4. 1-kb HindIII-ClaI fragment. The transcription region for the lacBl was identified on this fragment with promoter- and terminator-probe plasmids. The deduced sequence of 149 aa of the N-terminal part of lacBl showed aa sequence homology with beta-Gal from B. stearothermophilus, B. circulans, Haloferax alicantei, Clostridium perfringens, Arthrobacter sp.. No significant homology was shared with those found in the lacZ and lacS families. The recombinant beta-galactosidase (LacB1) was purified by FPLC. The molecular mass of the enzyme (80 kDa) and its optimal pH (5.7) and temperature (45 degrees C) were determined.

Phage abortive infection of Bacillus licheniformis ATCC 9800; identification of the abiBL11 gene and localisation and sequencing of its promoter region.

The virulent bacteriophage BL11 infects almost all Bacillus licheniformis strains tested, including the industrial bacitracin-producing B. licheniformis 19. B. licheniformis ATCC 9800, however, was virtually insensitive to phage BL11 infection, and all of the few surviving progeny phages proved to be mutants. The phage-resistance mechanism was neither inhibition of adsorption, nor restriction or exclusion provided by a resident prophage, but was, instead, of another type. Phage BL11 adsorbed well on to ATCC 9800 cells, its DNA was injected, but replication of phage DNA was inhibited and the infected cells died. Thus, the mechanism of phage resistance was identified as abortive infection (AbiBL11). The so-called abiBL11 gene was identified on the chromosome of strain ATCC 9800 by Tn917PF1 transposon mutagenesis. Part of the abiBL11 gene from the phage-sensitive ATCC 9800::Tn917PFI was cloned. Gene-disruption analysis, based on Campbell-type integration, showed that a 0.3-kb EcoRI fragment contained the 5' end of abiBL11. The promoter region of abiBL11 was identified using promoter- and terminator-probe plasmids. The deduced sequence (206 amino acids) of the N-terminal part of abiBL11 showed no significant homology to known abortive-infection genes, but did show homology to a Saccharomyces cerevisiae gene coding for a serine/threonine protein kinase (RCK1).

Lung pathology of fatal severe acute respiratory syndrome.

BACKGROUND: Severe acute respiratory syndrome (SARS) is a novel infectious disease with global impact. A virus from the family Coronaviridae has been identified as the cause, but the pathogenesis is still unclear. METHODS: Post-mortem tissue samples from six patients who died from SARS in February and March, 2003, and an open lung biopsy from one of these patients were studied by histology and virology. Only one full autopsy was done. Evidence of infection with the SARS-associated coronavirus (SARS-CoV) and human metapneumovirus was sought by reverse-transcriptase PCR and serology. Pathological samples were examined by light and electron microscopy and immunohistochemistry. FINDINGS: All six patients had serological evidence of recent infection with SARS-CoV. Diffuse alveolar damage was common but not universal. Morphological changes identified were bronchial epithelial denudation, loss of cilia, and squamous metaplasia. Secondary bacterial pneumonia was present in one case. A giant-cell infiltrate was seen in four patients, with a pronounced increase in macrophages in the alveoli and the interstitium of the lung. Haemophagocytosis was present in two patients. The alveolar pneumocytes also showed cytomegaly with granular amphophilic cytoplasm. The patient for whom full autopsy was done had atrophy of the white pulp of the spleen. Electron microscopy revealed viral particles in the cytoplasm of epithelial cells corresponding to coronavirus. INTERPRETATION: SARS is associated with epithelial-cell proliferation and an increase in macrophages in the lung. The presence of haemophagocytosis supports the contention that cytokine dysregulation may account, at least partly, for the severity of the clinical disease. The case definition of SARS should acknowledge the range of lung pathology associated with this disease.

Pregnancy and perinatal outcomes of women with severe acute respiratory syndrome.

OBJECTIVE: This study was undertaken to evaluate the pregnancy and perinatal outcomes of pregnant women with severe acute respiratory syndrome (SARS). STUDY DESIGN: All pregnant women (12) who presented with SARS in Hong Kong between February 1 and July 31, 2003, were included. The pregnancy and perinatal outcomes were collected. Evidence of perinatal transmission of virus was assessed with the SARS-associated coronavirus reverse-transcriptase polymerase chain reaction on cord blood, placenta tissue, and subsequent follow-up of the neonate on serology. RESULTS: Three deaths occurred among the 12 patients, giving a case fatality rate of 25%. Four of the 7 patients (57%) who presented in the first trimester had spontaneous miscarriage. Four of the 5 patients who presented after 24 weeks were delivered preterm. Two mothers recovered without delivery, but their ongoing pregnancies were complicated by intrauterine growth restriction. No newborn infant had clinical SARS and all investigations were negative for SARS. CONCLUSION: SARS during pregnancy is associated with high incidences of spontaneous miscarriage, preterm delivery, and intrauterine growth restriction. There is no evidence of perinatal SARS infection among infants born to these mothers.