- Volume 142, Issue 6, 1996
Volume 142, Issue 6, 1996
- Pathogenicity And Medical Microbiology
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Utilization of transferrin and salmon serum as sources of iron by typical and atypical strains of Aeromonas salmonicida
More LessThe ability of typical and atypical strains of Aeromonas salmonicida to utilize non-haem sources of protein-bound iron was evaluated. (i) In a plate bioassay, the suppression of growth imposed on typical and atypical A. salmonicida by addition of the high-affinity iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid) (EDDA) to the growth medium was reversed by the addition of 30% or 90% iron-saturated bovine or human transferrin (Tf) or lactoferrin (Lf) to the growth medium. (ii) The mechanism of obtaining iron from Tf was investigated by the addition of bovine Tf contained within a dialysis bag. The reversal of iron-restricted growth suppression differed between the strains in that the atypical strains were unable to utilize Tf contained within a dialysis bag while the typical strains were able to do so. This suggested a siderophore-mediated uptake of iron from Tf by the typical strains, which are known to produce siderophores while atypical strains do not. (iii) A solid-phase binding assay using horseradish-peroxidase-conjugated or biotinylated Tf or Lf failed to detect Tf/Lf-binding activity using whole typical or atypical cells. (iv) When atypical extracellular products (ECP) plus bovine Tf or salmon serum were enclosed in a dialysis bag, diffusible products were released which could reverse the EDDA-imposed growth suppression of an atypical strain. This reversal was negated by inhibition of the ECP metalloprotease with EDTA. (v) Purified 70 kDa serine protease of a typical strain was able to digest bovine Tf to low molecular mass fragments as observed in SDS-PAGE. These results indicate that typical and atypical strains of A. salmonicida differ in their mechanism of utilization of non-haem protein-bound sources of iron. Typical strains utilize Tf via a siderophore-mediated mechanism and are also able to digest Tf with the extracellular serine protease. Atypical strains utilize Tf by a siderophore-independent mechanism probably involving the proteolytic degradation of Tf by the extracellular metalloprotease.
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- Physiology And Growth
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Fuse1 alcohols induce hyphal-like extensions and pseudohyphal formationin yeasts
More LessAt a concentration of 0*5% (vlv), isoamyl alcohol induced the formationof hyphal-like extensions in haploid and diploid strains of Saccharomyces cerewisiae in liquid complex medium. These extensions, which develop via budinitiation and elongation, undergo DNA replication and nuclear division andappear similar in many respects to an aberrant form of the cell division cycle. However, in 025 % (vh) isoamyl alcohol, 5. cerewisiae formed pseudohyphae. Other ‘fusel’ alcohols (which are the products of amino acid catabolism) also induced hyphal-like extensions in this yeast, with n-amyl alcohol being as equally effective as isoamyl alcohol. lsoamyl alcohol induced the formation of pseudohyphae in two species of Candida and both hyphal-like extensions and pseudohyphae in Brettanomyces anomalus, suggesting a close relationship or a common basis to the development of the two morphologies.
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Adaptive response of the archaeon Sulfolobus acidocaldarius BC65 to phosphate starvation
More LessThe adaptive response of the archaeon Sulfolobus acidocaldarius BC65 to phosphate starvation was studied. When cells were subjected to phosphate limitation, their growth was affected. In addition, the levels of synthesis and/or the degree of phosphorylation of several proteins changed, as detected by two-dimensional nonequilibrium pH gradient electrophoresis of cells labelled in vivo with [35S]methionine and [35S]cysteine, or H3 32PO4. After another growth-restricting treatment, a heat shock, a general inhibition of protein synthesis was observed. Under phosphate starvation conditions, a 36 kDa protein became phosphorylated without its synthesis being significantly modified, suggesting a probable regulatory role during adaptation of the cell to the change in the external environment. In Southern blot analysis with specific probes from very conserved regions of the phoR and phoB genes from Escherichia coli, a positive hybridization with S. acidocaldarius BC65 chromosomal DNA fragments was found. This suggested the presence in S. acidocaldarius BC65 of genes related to the E. coli genes involved in the phosphate starvation response system. This appears to be the first evidence of the possible existence of a two-component sensory system in a micro-organism from the archaeal kingdom Crenarchaeota.
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- Plant-Microbe Interactions
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A putative cyclic peptide efflux pump encoded by the TOXA gene of the plant-pathogenic fungus Cochliobolus carbonum
More LessRace 1 isolates of Cochliobolus carbonum are pathogenic on certain maize lines due to production of a host-selective cyclic tetrapeptide, HC-toxin. Flanking HTS1, which encodes the central enzyme in HC-toxin biosynthesis, a gene was identified and named TOXA. Like HTS1, TOXA occurred only in isolates of the fungus that make HC-toxin and was present as two linked copies in most toxin-producing isolates. HTS1 and TOXA were transcribed in the opposite orientation and their transcriptional start sites were 386 bp apart. The predicted product of TOXA was a 58 kDa hydrophobic protein with 10-13 membrane-spanning regions. The sequence was highly similar to several members of the major facilitator superfamily that confer resistance to tetracycline, methylenomycin, and other antibiotics. Although it was possible to mutate one copy or the other of TOXA by targeted gene disruption, numerous attempts to disrupt both copies in a single strain were unsuccessful, suggesting that TOXA is an essential gene in strains that synthesize HC-toxin. On the basis of its presence only in HC-toxin-producing strains, its proximity to HTS1 and its predicted amino acid sequence, we propose that TOXA encodes an HC-toxin efflux pump which contributes to self-protection against HC-toxin and/or the secretion of HC-toxin into the extracellular milieu.
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- Genome Analysis
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Determination of a 12 kb nucleotide sequence around the 76° region of the Bacillus subtilis chromosome
More LessThe nucleotide sequence of a 12361 bp DNA segment in the 760 region of the Bacillus subtilis chromosome has been determined. Ten putative ORFs were identified. The deduced amino acid sequences of the products of two of them (glv-1 and glv-2) exhibited high similarity to those of glvG (6-phospho-β-glucosidase gene) and glvC [permease (the IIC domain) of the phosphotransferase system (PTS)], respectively, in the glv operon of Escherichia coli. The C-terminal region of Glv-2 exhibited similarity to the entire region of GlvB (the IIB domain of PTS) of E. coli, suggesting fusion of the glvC and glvB genes in B. subtilis. glv-1, yfiA and glv-2 seem to form an operon of a phosphoenolpyruvate:sugar PTS, followed by a presumed four-membered operon of an ABC transport system. Moreover, a presumed sugar symporter and its regulatory genes were located in this region.
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Sizing chromosomes and megaplasmids in haloarchaea
More LessPFGE was used for the genomic analysis of different species and strains belonging to four out of the six recognized haloarchaeal (halobacterial) genera. All of them were found to carry one chromosome from 1.8-3 Mb, and usually several, but at least one, large plasmids of approximately 90-680 kb, which were detected in supercoiled and linear forms. From the data gathered, chromosomal size appears to be conserved at genus level, whereas plasmid composition and size seems to be subjected to certain variability.
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Size and genomic location of the pMGA multigene family of Mycoplasma gallisepticum
More LessThe pMGA multigene family encodes variant copies of the cell surface haemagglutinin of Mycoplasma gallisepticum. Quantitative Southern blotting, using an oligonucleotide probe complementary to a region conserved in the leader sequence of all known pMGA genes, was used to estimate the number of members of the family in the genome of seven strains of M. gallisepticum. The number of copies estimated to be present in the genome varied from 32 in strain F to 70 in strain R, indicating that the pMGA gene family may be second in size only to the tRNA family among prokaryotes. If all members of the pMGA family are of similar length to those which have been characterized, a minimum of 79 kb (7.7%) of the genome of strain S6, 82 kb (8.2%) of PG31 and 168 kb (16%) of the genome of strain R is dedicated to encoding variants of the same haemagglutinin. The GAA repeat motif identified in the intergenic region between all characterized pMGA genes appeared to be a feature common to most, if not all, pMGA genes, and furthermore probably exclusive to them. The genomic locations of members of the pMGA family were determined by PFGE and Southern blot hybridization of M. gallisepticum strain S6. The hybridizing regions were localized to four separate regions on the chromosome. The pMGA genes are likely to be predominantly arranged as tandem repeats within these regions, similar to the restricted regions for which the genomic sequence has been determined.
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- Corrigendum
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