Journal of general microbiology最新文献

Reproduction by binary fission generates a clonal genetic structure in bacterial populations in the absence of a high rate of recombination. The extent of recombination in natural populations of Neisseria gonorrhoeae was determined from an analysis of electrophoretically demonstrable allelic variation at structural genes encoding nine enzyme loci in 227 worldwide isolates. No significant linkage disequilibrium was evident in the population, indicating that recombination must be frequent, relative to binary fission. The genetic structure of N. gonorrhoeae was compared with that of Bacillus subtilis from an earlier study. Linkage disequilibrium was less extreme in the N. gonorrhoeae population than in the local population of B. subtilis, in which only modest clonal structure was evident. Thus, N. gonorrhoeae, unlike pathogens so far examined, has a non-clonal population structure. As expected in a freely recombining population, no correlation was found between electrophoretic genotype and serovar or auxotype.

Glucose-6-phosphate dehydrogenase (G6PD; D-glucose 6-phosphate:NADP+ oxidoreductase, EC 1.1.1.49) has been purified from Aspergillus nidulans and Aspergillus niger by a combination of affinity and anion exchange chromatography. A 500-1000-fold purification was obtained and the final enzyme preparations were shown to be pure but not homogeneous. For both fungi the purified enzyme preparation gave two bands on native and denaturing gels. The catalytically active form is a multimer. The molecular mass of the monomers is 60 and 57 kDa for A. nidulans and 55 and 53 kDa for A. niger. Both enzymes exhibited strict specificity towards both substrates glucose 6-phosphate and NADP+. The A. nidulans and A. niger G6PD enzymes catalyse the conversion of glucose 6-phosphate via a random order mechanism. Inhibition studies provided evidence for the physiological role of G6PD as producer of NADPH in both fungi.

Seven mosquito-specific strains of Bacillus thuringiensis isolated in Japan were examined for their flagellar (H) antigenicities and the properties of parasporal inclusion proteins. They were assigned to six H serovars: serovar fukuokaensis (H 3ade); serovar canadensis (H 5ac); serovar darmstadiensis (H 10); serovar kyushuensis (H 11ac); serovar shandongiensis (H 22); and an undescribed serovar belonging to H serotype 20. Purified parasporal inclusions exhibited moderate mosquito larvicidal activities with LC50 values ranging from 1 microgram ml-1 to 10 micrograms ml-1. The inclusions of these strains consisted of highly heterogeneous multiple protein components, and five distinct patterns were evident in their SDS-PAGE profiles. Antibodies against kyushuensis inclusion proteins were reactive with all strains to varying degrees, while israelensis antibodies gave only relatively weak reactions with the seven strains. Similarity in antibody-binding profiles was associated with similarity in SDS-PAGE profiles. In a given strain, different antisera gave altered immunoblot profiles. Haemolytic activity was shown by solubilized parasporal inclusion proteins of five of the seven strains.

Synthetic oligonucleotides, which were designed according to amino acid sequences conserved between Rhodospirillum rubrum and Azospirillum brasilense DraT and DraG, respectively, were used to identify the corresponding genes of Rhodobacter capsulatus. Sequence analysis of a 1904 bp DNA fragment proved the existence of R. capsulatus draT and draG. These two genes were separated by 11 bp only, suggesting that R. capsulatus draT and draG were part of one transcriptional unit. In contrast to R. rubrum, A. brasilense and Azospirillum lipoferum, the R. capsulatus draTG genes were not located upstream of the structural genes of nitrogenase nifHDK but close to the dctP gene at a distance of about 1000 kb from the nifHDK genes. Deletion mutations in the draTG gene region were constructed and introduced into R. capsulatus wild-type and a nifHDK deletion strain. The resulting mutant strains were examined for post-translational regulation of the molybdenum and the alternative nitrogenase in response to ammonia and darkness. Under 'switch-off' conditions the modified (ADP-ribosylated) and the non-modified forms of component II of both the molybdenum and the alternative nitrogenase were detected in a draTG wild-type background by immunoblot analysis, whereas only the non-modified forms were present in the draTG deletion strains. Nitrogenase activity in these strains was followed by the acetylene reduction assay. In contrast to the wild-type, draTG mutants were not affected in nitrogenase activity in response to ammonia or darkness. These results demonstrated that the draTG genes are required for post-translational regulation of both the molybdenum and the heterometal-free nitrogenase in R. capsulatus.

In wild-type Streptomyces ambofaciens ATCC 23877, pigment-defective (Pig-) mutants arise at a frequency of about 0.5%; this genetic instability is related to genomic rearrangements such as deletions and/or amplifications of DNA sequences. On media containing oxolinic acid and novobiocin, which interact with the A and B subunits of DNA gyrase, respectively, the frequency of variants increased dramatically. The Pig- mutant frequency was increased to almost 100% on a medium containing oxolinic acid at a concentration allowing 55% survival. On solid medium containing either oxolinic acid or novobiocin at subinhibitory concentrations, most colonies exhibited a 'patchwork' phenotype, characterized by the presence of numerous Pig- sectors. Similar phenomena were not observed on media containing the transcriptional inhibitor rifampicin or the translational inhibitor streptomycin. Many of the Pig- mutants exhibited a pleiotropic phenotype and were affected in aerial mycelium formation, colony growth and/or prototrophy. Moreover, the same kinds of rearrangements (deletions and/or amplifications of DNA sequences) were found in both induced and spontaneous Pig- mutants. The results suggest either that DNA gyrase is directly involved in genetic instability or that an SOS-like system is implicated.

Members of the Streptococcus milleri group (SMG) that react with Lancefield group C antisera were shown to bind large amounts of albumin although there was no direct relation between these two properties as polyclonal antisera to Lancefield group C antigen did not prevent the binding of albumin. There was a specificity for albumin binding, with albumin from man, monkeys, cat, dog and mouse being bound to a greater degree than albumin from cow, horse, goat or rabbit. Gold-labelled albumin was shown to be located close to the surface of strains by transmission electron microscopy. A cell-surface protein of M(r) 24,000, which was liberated by lysozyme treatment of cells, was shown to be the cell-surface receptor on Streptococcus intermedius C5. The receptor was physically dissimilar from protein G, an albumin- and IgG-binding protein of 'large-colony' Lancefield group C and G streptococci.

It has been long known that the migrating slugs of the cellular slime moulds are highly sensitive to their environment and orient towards light and in temperature and chemical gradients. There is considerable evidence from past work that these orientations are governed by NH3 which affects the rate of movement of cells within the slug with such precision that orientation to the external stimuli is achieved. In order to test this hypothesis further, various ways to alter the internal NH3 concentration were devised. Substances that either increased or decreased proteolysis were applied to one side of the tip of a slug, thereby affecting its orientation. Some of the treatments strongly support the role of internally produced NH3 in orientation, and all the treatments produce results that are consistent with the hypothesis.

Previous studies have shown that gas vesicles isolated from the cyanobacterium Anabaena flos-aquae contain two types of protein, GvpA, a small hydrophobic protein that forms the main ribbed structure, and GvpC, a protein comprising five repeats of a 33-amino-acid-residue motif, which is located on the outer surface of the GvpA shell. GvpC was shown to increase the critical collapse pressure of the gas vesicles; it was thought to do this by forming a series of molecular ties that bind the ribs together. We now show that antibodies raised against GvpC label both the central cylinders and the conical end caps of native gas vesicles but fail to bind to gas vesicles that have been stripped of GvpC. The molar ratio of GvpA to GvpC has been calculated from amino acid analyses of gas vesicle hydrolysates by reference to the abundance of amino acids that occur predominantly or exclusively in one protein or the other; the molar ratio was found to be 25:1 in freshly isolated gas vesicles and 23:1 in gas vesicles saturated with GvpC. We have considered three ways in which the 33-residue repeats of GvpC might interact with the crystallographic unit cell of GvpA molecules in the ribs. The Anabaena GvpC will bind to and restore the strength of gas vesicles isolated from Aphanizomenon and Microcystis that lack their native GvpC.

Transposon mutagenesis and antibiotic enrichment were employed to isolate a mutant of Rhodobacter sphaeroides Si4 designated strain M22, that had lost the ability to grow on D-mannitol and to produce the enzyme mannitol dehydrogenase (MDH). DNA flanking the transposon in the mutant strain was used as a probe for the identification and cloning of the MDH gene (mtlK). A 5.5 kb EcoRI/BglII fragment from R. sphaeroides Si4 was isolated and shown to complement the mutation in R. sphaeroides M22. Successful complementation required that a promoter of the vector-plasmid pRK415 be present, suggesting that the mtlK gene is part of a larger operon. Using oligonucleotides derived from the N-terminal sequence of MDH as probes mtlK was located on the complementing fragment and the gene was sequenced. The mtlK open reading frame encodes a protein of 51,404 Da with an N-terminal sequence identical to that obtained from amino acid analysis of the purified MDH. The MDH of R. sphaeroides Si4 exhibits distant similarity to the mannitol-1-phosphate dehydrogenases from Escherichia coli and Enterococcus faecalis, with 28.1% and 26.3% identity, respectively. Mutant strains deficient in MtlK displayed substantial levels of sorbitol dehydrogenase activity, originally thought to be only a minor activity associated with the MDH enzyme. It is likely that we have uncovered an additional polyol dehydrogenase with activity for sorbitol. The mtlK gene can be used for overexpression of MDH in E. coli in order to obtain sufficient amounts of enzyme for further investigations and applications.

A group of Campylobacter-like organisms (CLOs) were isolated from the faeces of diarrhoeic or healthy dogs, constituting 4% of all CLOs from this source. Since they formed a unique DNA homology group within the genus Helicobacter, and exhibited distinctive phenotypic properties, they were collectively termed the HC group. A polyphasic taxonomic analysis was made of this group. The phenotype of four dog isolates and a single human isolate was unique and could be distinguished bacteriologically from other helicobacters. Electron microscopic ultrastructure revealed defining characteristics of Helicobacter. The 16S rRNA gene of the nominated type strain NCTC 12739T was sequenced, and its analysis delineated the group as a new species of Helicobacter. This conclusion was supported by relative DNA homology and whole-cell protein electrophoretic patterns. We therefore propose the name Helicobacter canis sp. nov. for this group. The species most closely related to H. canis sp. nov. were H. cinaedi, 'Flexispira rappini' and H. fennelliae. A species-specific recombinant DNA probe was cloned from NCTC 12739T for use in routine laboratory identification and epidemiological studies. The faecal source, bile tolerance and lack of urease activity of H. canis sp. nov. suggest that this new Helicobacter species colonizes the lower bowel rather than the stomach.