Journal of general microbiology最新文献

This paper describes the characterization and taxonomic status of N16, a chlamydial isolate from the respiratory tract of a horse. N16 contains plasmid DNA, has normal elementary body morphology and its inclusions do not stain with iodine. Its major outer-membrane protein (MOMP) gene was completely sequenced and compared with the MOMP genes of Chlamydia pneumoniae, C. psittaci, C. trachomatis and C. pecorum. This analysis revealed that N16 is closely related to the TWAR strain of C. pneumoniae (94.5% and 94.4% DNA homology with TWAR isolates IOL-207 and AR-39 respectively). By comparison, N16 shows between 72.1% and 73.7% DNA homology with C. psittaci strains, 70.9% and 71.1% homology with C. pecorum strains LW613 and 1710S and 69.2% homology with C. trachomatis serotype E. The MOMP gene of N16 shares 93.8% DNA homology with the MOMP gene of a chlamydial isolate KC from the conjunctiva of a koala. Monoclonal antibodies raised to C. pneumoniae IOL-207 and shown to be C. pneumoniae-specific confirmed that N16 was more closely related to C. pneumoniae than to C. psittaci. Thus DNA homology and monoclonal antibody data both suggest that horse chlamydiae, as exemplified by N16, form a new second strain of C. pneumoniae. This species is probably more widespread and diverse than the current literature would suggest.

The lacE and lacG genes from Streptococcus mutans have been isolated and characterized, and their nucleotide sequence has been determined. The lacE gene encodes the lactose-specific Enzyme II component of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The lacG gene encodes the phospho-beta-galactosidase which cleaves the lactose phosphate that is formed by the lactose PTS. The S. mutans lacE and lacG genes are located in the same operon as the tagatose genes. S. mutans metabolizes lactose via the tagatose phosphate pathway. The deduced LacE and LacG proteins of S. mutans display high homology with the corresponding proteins from Lactococcus lactis, Staphylococcus aureus and Lactobacillus casei.

Pseudomonas sp. strain CF600 can degrade phenol and some of its methylated derivatives via a plasmid (pVI150)-encoded pathway. The metabolic route involves hydroxylation by a multi-component phenol hydroxylase and a subsequent meta-cleavage pathway. All 15 structural genes involved are clustered in an operon that is regulated by a divergently transcribed transcriptional activator. The multi-component nature of the phenol hydroxylase is unusual since reactions of this type are usually accomplished by single component flavoproteins. We have isolated and analysed a number of marine bacterial isolates capable of degrading phenol and a range of other aromatic compounds as sole carbon and energy sources. Southern hybridization and enzyme assays were used to compare the catabolic pathways of these strains and of the archetypal phenol-degrader Pseudomonas U, with respect to known catabolic genes encoded by Pseudomonas CF600. All the strains tested that degraded phenol via a meta-cleavage pathway were found to have DNA highly homologous to each of the components of the multicomponent phenol hydroxylase. Moreover, DNA of the same strains also strongly hybridized to probes specific for pVI150-encoded meta-pathway genes and the specific regulator of its catabolic operon. These results demonstrate conservation of structural and regulatory genes involved in aromatic catabolism within strains isolated from diverse geographical locations (UK, Norway and USA) and a range of habitats that include activated sludge, sea water and fresh-water mud.

In a search for the mechanism underlying dimensional changes in bacteria, the glucose analogue methyl alpha-D-glucoside was used to effect a rapid reduction in the mass growth rate of Escherichia coli by competitively inhibiting glucose uptake, a so-called nutritional shift-down. The new steady-state cell mass and volume were reached after 1 h, during which the rate of cell division was maintained; rearrangement of the linear dimensions (cell length, diameter), however, required an additional 2 h and caused an undershoot in cell length, consistent with the view that E. coli is slow to modify its diameter. The results are compared with the overshoot in cell length that occurs following nutritional shift-up.

Continuous and recycling cultures were carried out with Aspergillus niger N402 wild-type and a glucoamylase overproducing transformant to investigate growth and product formation characteristics. In shake flask cultures, the amount of glucoamylase produced by the transformant was about five times more than by the wild-type strain. In contrast with these results, a twofold overproduction was found in glucose-limited continuous cultures, while no overproduction was found under maltodextrin-limitation. Two regions of specific growth rates could be distinguished, one at specific growth rates lower (domain I) and one at specific growth rates higher than 0.12 h-1 (domain II). In domain I changes in mycelium morphology and conidia formation were observed. It has been concluded that maintenance requirements are dependent on the specific growth rate over the whole range of measured growth rates. The deviation in linearity in the linear equation of substrate utilization, caused by this phenomenon, should be considered when continuous cultures with filamentous fungi are performed. In recycling cultures, xylose as limiting carbon source repressed glucoamylase production very strongly. Under maltodextrin-limitation a fivefold overproduction was found. After about 150 h , the total amount of glucoamylase produced was still increasing, while total amount of product, measured as carbon, remained constant. After this time no increase in the amount of biomass formed was observed. These results suggest autolysis and cryptic growth taking place in a recycling fermenter and cell death rate equalling growth rate.

The sequences of the por genes, encoding outer-membrane protein PI, have been obtained from a number of strains of Neisseria gonorrhoeae that express PIA molecules with differing serovar specificities. The inferred amino acid sequences of the mature proteins each comprise 308 residues and show considerable homology, with the degree of sequence variation between PIA molecules being considerably less than seen previously with PIB, but more evenly distributed throughout the molecule. The positions of sequence variation are largely confined to the regions predicted to form one of eight surface-exposed loops, suggesting a more widespread distribution of potential antigenic diversity. The deduced amino acid sequences were used to synthesize peptides for epitope mapping experiments. Some epitopes responsible for serovar specificity or recognized by bactericidal monoclonal antibodies could be identified on the basis of their reactivity with simple linear peptides, whilst others recognized conformational epitopes. By comparison of sequence differences with mAb reactivity it was possible to identify regions that appear to contribute to such determinants, including separated regions of the molecule which together were required for the formation of the conformational epitopes. All the epitopes identified lie at or close to the apices of the predicted surface-exposed loops 1, 3, 6, or 8, focusing attention on these regions as accessible targets for immune attack.

Catabolism of isonicotinate by Mycobacterium sp. INA1 has been shown to proceed via 2-hydroxyisonicotinate, 2,6-dihydroxyisonicotinate (citrazinate), citrazyl-CoA and 2,6-dioxopiperidine-4-carboxyl-CoA. An extended pathway involving propane-1,2,3-tricarboxylate as a further intermediate is presented in this paper. Propane-1,2,3-tricarboxylate was oxidized stepwise to 2-oxoglutarate involving an oxidase, aconitase and isocitrate dehydrogenase. Isonicotinate dehydrogenase catalyses the first step of isonicotinate metabolism in Mycobacterium sp. INA1. The enzyme was purified to apparent homogeneity by a three-step procedure. Enrichment was accompanied by partial loss in specific activity. The native enzyme had a molecular mass of either 125 kDa or 250 kDa, when estimated by native gradient PAGE or gel filtration, respectively. SDS-gel electrophoresis revealed three types of subunits with molecular masses of approximately 83, 31 and 19 kDa. N-Terminal amino acid sequences of all three subunits have been determined. Molybdenum, iron, acid-labile sulphur and FAD were present at molar ratios of 1, 4, 4, 1 per protomer (125 kDa). The molybdenum-complexing cofactor was shown to be molybdopterin cytosine dinucleotide. Besides isonicotinate, only quinoline-4-carboxylate was found to be oxidized at appreciable rates.

Valine aminotransferase, a key enzyme in both biosynthesis and breakdown of branched-chain amino acids, showed consistently higher activity in Candida utilis grown in continuous culture than in Saccharomyces cerevisiae, while pyruvate decarboxylase and alcohol dehydrogenase, the other two enzymes of the Ehrlich pathway of branched-chain alcohol formation, were lower in activity. By spheroplast lysis, it was shown that valine aminotransferase followed the distribution of pyruvate decarboxylase in being located in the cytosol. Replacement of ammonium as nitrogen source by valine during conditions of carbon or nitrogen limitation caused increased specific activities of these three enzymes in S. cerevisiae, but (with one exception) decreased those of C. utilis. Of the metabolites accumulating in the culture medium, little or no ethanol or branched-chain alcohols were present during carbon-limited growth of either organism, but the change to nitrogen limitation resulted in increases in concentration of 20- to 100-fold in pyruvate, acetate and non-pyruvate keto acids as well as the accumulation of branched-chain alcohols in both organisms, and of ethanol, ethyl acetate and glycerol in S. cerevisiae. When valine was the limiting nitrogen source, there was an increase in non-pyruvate keto acids and a 10- to 16-fold increase in 2-methylpropanol. Total branched-chain alcohols formed under nitrogen limitation were 2-fold higher in S. cerevisiae than in C. utilis, irrespective of nitrogen source. Accumulation of branched-chain alcohols, ethanol, acetate and glycerol was also observed during carbon-limited growth of S. cerevisiae with valine as nitrogen source at dilution rates above the critical rate for transition to respirofermentative growth. Less than 70% of the valine carbon metabolized during growth of S. cerevisiae and only 15% of that used during growth of C. utilis was recovered in identified metabolic products. Even allowing for losses by volatilization during aeration, this suggests that a significant amount of the valine is being metabolized by a route or routes other than the Ehrlich pathway, possibly via the action of branched-chain 2-keto acid dehydrogenase. The molar growth yield for the nitrogen source under either carbon or nitrogen limitation was significantly lower for growth on valine than for growth on ammonium, suggesting that breakdown of valine requires more energy. It is evident that not all the enzymes involved in branched-chain amino acid metabolism in yeasts have yet been identified, nor are their interactions properly understood.

The genetic loci leading to anaerobic derepression of a sodA::lacZ protein fusion in a UV-generated mutant strain (UV14) of Escherichia coli were identified. The mutant (UV14) was found to harbour two altered loci: one is in the trans-regulatory gene fnr (fumarate nitrate reduction) where leucine-129 was changed to glutamine (fnr14), and the second (sodA14) is in the promoter region (cis) of the sodA gene apparently affecting the binding of the Fur (ferric uptake regulation) protein. Introduction of an fnr+ gene into UV14 restored anaerobic repression of sodA::lacZ and restored the ability of the cells to reduce nitrate. However, when either the fnr14 or the sodA14 mutation was introduced into an otherwise wild-type background, only slight anaerobic derepression of sodA was observed. When both the cis- and trans-acting mutations (i.e. sodA14 and fnr14) were combined simultaneously in an otherwise wild-type background, the specific activity of sodA::lacZ expression was comparable to that of the original mutant strain (UV14). Furthermore, a genetically confirmed fur fnr double mutant was also similarly derepressed in anaerobic sodA::lacZ expression. The data presented suggest that the cis-mutation in UV14 (sodA14) affects the Fur-binding site in the sodA promoter, while having no effect on Fnr or Arc mediated repression. Also, a second putative Fnr-binding site that straddles the ribosomal binding-site was identified in the sodA gene.

Genetic instability in Streptomyces ambofaciens DSM 40697 is correlated with genomic instability characterized by multiple rearrangements (deletions and/or amplifications) occurring in a large unstable region. We have focused on one of the two amplifiable DNA loci which were mapped in this region: the amplifiable unit of DNA locus 6 (AUD6). The nucleotide sequence of one AUD6 fragment of 1.9 kb reveals the presence of two open reading frames (ORF1 and ORF2) on the basis of the typical Streptomyces base composition at each of the three positions within codons. ORF1 shows some similarity with a gene encoding a regulatory protein. The presence of potential genes in this unstable locus was unexpected because deletions occurred with high frequency within this region in the genetic instability-derived mutant strains. However, transcription analyses by S1 nuclease protection experiments on the wild-type strain showed transcription of both ORF1 and ORF2. Moreover, the amplified strain reveals increased transcription of ORF1 but no transcription of ORF2. The amplification therefore results in a switch in transcription. The unstable region of S. ambofaciens DSM 40697 therefore is not a 'silent' region because at least some loci are transcribed.