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J H Croft

Publications and source records attributed to J H Croft.

16 recordsLinked to original sources
PubMed1997

Recombination of mitochondrial DNAs following transmission of mitochondria among incompatible strains of black Aspergilli.

Successful intra- and interspecific mitochondrial transfers were performed by polyethylene glycol (PEG)-induced protoplast fusion among incompatible strains belonging to the Aspergillus niger species aggregate. The mitochondrial DNAs (mtDNAs) of the strains examined were of three main types based on their restriction fragment length polymorphism (RFLP) profiles. mtDNA types 1 and 2 correspond to A. niger and A. tubingensis species, respectively, while type 3 is represented by some Brazilian wild-type isolates (possibly a distinct species or subspecies). mtDNA types 1 and 2 could be further divided into several subgroups (1a-1e and 2a-2f). All these strains, representing different RFLP groups or subgroups, were fully incompatible with respect to nuclear complementation. The transfer experiments were carried out under selection pressure, using a mitochondrial oligomycin-resistant mutant of mtDNA type 1a as donor. Following fusion mitochondrial oligomycin-resistant progenies were recovered in the presence of oligomycin by selecting for the nuclear phenotypes of the oligomycin-sensitive recipient strains. All attempted transfers were successful, and resulted in different varieties of resistant recombinant mitochondrial progenies at various frequencies. Within the group of strains of mtDNA type 1, the transfer of oligomycin-resistant mitochondria resulted in the appearance of a single recombinant type of RFLP profile in each case. The recombination events were more complex when the transfer of oligomycin resistance occurred between strains representing different species (mtDNA groups 1a-->2 and 1a-->3). A great variety of recombinant mtDNA RFLP profiles appeared. Explanation for this phenomenon are discussed on the basis of preliminary physical mapping data.

Anti-Bacterial Agents↗
PubMed1997

Molecular and phenotypic characterization of Aspergillus japonicus and Aspergillus aculeatus strains with special regard to their mitochondrial DNA polymorphisms.

Forty Aspergillus japonicus and A. aculeatus strains, most of them wild-type isolates, were examined using various molecular and phenotypic techniques. The rDNAs proved to be invariable (even strains of the species A. aculeatus exhibited the same restriction profile), while the strains could be classified into seven different mtDNA RFLP groups. Hybridisation data suggest that six of these mtDNA types have certain common restriction sites, while mtDNA type 7, which was exhibited by some A. aculeatus strains, probably has quite different mtDNA organisation and their size was smallest among the strains studied. The RAPD technique and isoenzyme analysis revealed some variabilities within these RFLP groups and strain specific features could also be recognised. Carbon source assimilation spectra were found to be very distinctive for strains of A. japonicus, A. aculeatus and A. niger, providing a useful tool for pre-characterising new wild-type isolates of black Aspergilli. Only a limited correlation was observed between the dendrograms based on genotypic and phenotypic characters.

Aspergillus↗
PubMed1996

Molecular polymorphism and phenotypic variation in Aspergillus carbonarius.

Thirteen collection strains and field isolates of Aspergillus carbonarius were examined by using various genotypic and phenotypic approaches. Restriction fragment length polymorphism analysis of the ribosomal RNA gene cluster and the mitochondrial DNA of the strains revealed only slight variations, except for one field isolate (IN7), which exhibited completely different ribosomal RNA gene cluster and mitochondrial DNA patterns. The mitochondrial DNAs of these strains were found to be much larger (45 to 57 kb) than those found earlier in the A. niger aggregate. Strain-specific characters could be detected by the random amplified polymorphic DNA technique. Isoenzyme analysis and examination of carbon source utilisation patterns of the strains also revealed some intraspecific variability, though much smaller than that observed by using DNA-based techniques. The dendrograms constructed based on genotypic and phenotypic data suggest that strain IN7 might represent a new subspecies of A. carbonarius.

Acid Phosphatase↗
PubMed1996

Mitochondrial inheritance in Aspergillus nidulans.

Mitochondrial chloramphenicol and oligomycin resistance mutations were used to investigate mitochondrial inheritance in A. nidulans. Mitochondrial RFLPs could not be used to distinguish between paternal and maternal mitochondria because none were detected in the 54 isolates investigated. Several thousand ascospores from each of 111 hybrid cleistothecia from 21 different crosses between 7 heterokaryon incompatible isolates were tested for biparental inheritance. All mitochondrial inheritance was strictly uniparental. Not one instance of paternal inheritance of mitochondria was observed. The implications of our results for the theory that uniparental inheritance evolved to avoid cytoplasmic conflict are discussed. Possible explanations for the maintenance of strict uniparental inheritance of mitochondria in an inbreeding homothallic organism are suggested. The chloramphenicol resistance marker was inherited preferentially to the oligomycin resistance marker probably due to the inhibited energy production of mitochondria with the oligomycin resistance mutation. The maternal parent was determined for 93 hybrid cleistothecia from 17 crosses between 7 different strains. Contrary to previous reports A. nidulans strains functioned as both maternal and paternal parent in most crosses.

Aspergillus nidulans↗
PubMed1994

Assignment of RFLP, RAPD and isoenzyme markers to Aspergillus nidulans chromosomes, using chromosome-substituted segregants of a hybrid of A. nidulans and A. quadrilineatus.

Chromosome-substituted haploid segregants were selected from among the benomyl-induced progeny of an interspecific hybrid produced by polyethylene-glycol-induced fusion of protoplasts of an Aspergillus nidulans 'master strain' and an A. quadrilineatus auxotrophic mutant. These segregants were examined by RFLP, RAPD, and isoenzyme analysis. The A. nidulans ribosomal repeat unit was assigned to chromosome V, while the benA and the pyrG genes were assigned to linkage groups VIII and I, respectively, of A. nidulans. None of the other cloned genes tested (gdhA, amdS and 25s rRNA) showed polymorphism between the two parents. The method was also used to assign RAPD markers and isoenzyme bands of beta-arylesterase, phosphatases, NAD-dependent malate dehydrogenase, and cellulase, to A. nidulans chromosomes and/or to their A. quadrilineatus equivalents. The isoenzyme and DNA sequences assigned to chromosomes could be used to saturate the genetic map of A. nidulans, or could serve as starting points for the construction of a genetic map of A. quadrilineatus. No method affording the same possibilities has been described so far in Aspergilli. This chromosome-assay method may be a useful alternative to pulsed-field-gel electrophoretic procedures for the assignment of molecular markers to chromosomes.

Aspergillus↗
PubMed1994

Double-stranded RNA mycoviruses in section Nigri of the Aspergillus genus.

Double-stranded RNA bands were detected electrophoretically in about 7% of natural isolates and in 13 of 51 collection strains belonging in section Nigri of the genus Aspergillus. The identity of these bands was proved by S1 nuclease and RNase treatment. Most of the virus-containing natural isolates came from Indonesia. Electron microscopic examination of the strains revealed the presence of virus-like particles in the mycelia of the strains examined. All of the virus-like particles were isometric and their size was around 30-35 nm, while some Indonesian isolates also contained virus-like particles in the size range 23-25 nm. It was possible to cure some of these strains of virus-like particles by mutagenic treatment. The four strains tested lost their virus-like particles and also their 'arginine-proline leaky' phenotype and became prototrophic. Virus transfer was possible among these four strains by protoplast fusion. It also proved possible to transfer mycoviruses into a more distantly related Aspergillus tubingensis strain by prolonged incubation of the polyethylene glycol treated protoplasts in osmotically stabilized medium. In spite of the finding that all Aspergillus foetidus and both Aspergillus heteromorphus strains examined contained double-stranded RNA segments and virus-like particles, no phenotypes related to the presence of these VLPs have been observed so far.

Aspergillus↗
PubMed1994

Mitochondrial DNA restriction fragment length polymorphisms in field isolates of the Aspergillus niger aggregate.

The mitochondrial DNAs (mtDNAs) and the ribosomal repeat unit (ribosomal DNA, rDNA) of black Aspergillus isolates collected in various parts of the world were examined. Wide-ranging mtDNA variation was observed in natural populations of the Aspergillus niger aggregate. Most isolates were classifiable as A. niger or Aspergillus tubingensis according to their rDNA and mtDNA patterns. The mtDNA variation was distributed unevenly in the populations studied. The mtDNAs of most of the isolates collected in Australia were of the A. tubingensis type, with an unexpectedly high degree of variation, while the rDNA of these isolates exhibited the same A. tubingensis pattern as that of isolates from other locations. Some other local populations displayed very little polymorphism in their mtDNA and rDNA. Hybridization experiments in which cloned A. niger and Aspergillus nidulans mtDNA fragments were used revealed that the two main mtDNA groups corresponding to A. niger and A. tubingensis are more distantly related than concluded earlier. Six of the 13 Brazilian isolates examined exhibited mtDNA and rDNA types different from those of all the other strains and could not be classified into the above species. Classical taxonomic examination of these strains is in progress.

Aspergillus↗
PubMed1993

Evidence for a multi-allelic heterokaryon incompatibility (het) locus detected by hybridization among three heterokaryon-compatibility (h-c) groups of Aspergillus nidulans.

A strain of heterokaryon-compatibility (h-c) group A was crossed sexually to strains of h-cB and h-cGL of Aspergillus nidulans. A back-crossing programme established that there were seven hetero-allelic heterokaryon compatibility (het) genes controlling somatic incompatibility between strains of h-cA and h-cB. A similar back-crossing programme between strains of h-cA and h-cGL confirmed that these two groups differ at six het loci. Previous work has shown that h-cB differs from h-cGL at two het loci, hetA on linkage group V and hetB on linkage group VI. As an allelic difference at a single het locus is enough to cause two strains to be heterokaryon incompatible, 15 alleles spread over seven het loci are necessary to explain the h-cA, h-cB, h-cGL triangular compatibility relationship. One het locus is multi-allelic and this locus must be either hetA or hetB.

Alleles↗
PubMed1993

Analysis of heterokaryon incompatibility between heterokaryon-compatibility (h-c) groups R and GL provides evidence that at least eight het loci control somatic incompatibility in Aspergillus nidulans.

Protoplast fusion was used to hybridize strains 99-6 (h-cR) and 7-141 (h-cGL) in the Birmingham collection of Aspergillus nidulans. A sparsely conidiating, brown-pigmented diploid strain (MA7) was isolated. Inocula from MA7 were haploidized on medium containing Benlate and a haploid progeny sample collected. Heterokaryon compatibility testing of selected progeny strains assayed each linkage group in turn and established that h-cR and h-cGL were hetero-allelic for heterokaryon incompatibility (het) loci located on linkage groups III and V. Two selected MA7 progeny strains were sexually crossed to an h-cGL strain. Compatibility classification of the progenies of these crosses indicated that three het genes were located on linkage group III and two on linkage group V. Combination of these results with previous work using h-c groups A, B and Q in comparison with h-cGL indicates that a minimum number of eight and a maximum number of 18 het loci, spread over five linkage groups, are necessary to explain the compatibility relationships among these five h-c groups.

Alleles↗
PubMed1990

Investigation of the het genes that control heterokaryon incompatibility between members of heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans.

A chromosome assay method was used to determine the heterokaryon compatibility relationships between strains belonging to heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans. A hybrid strain (RD15) was isolated following protoplast fusion of strains 65-5 (h-cA) and 7-141 (h-cG1). The morphology of RD15 was severely abnormal compared to diploid strains of A. nidulans produced from heterokaryon-compatible haploid parents. Inocula of RD15 were induced to haploidize on medium containing Benlate and a parasexual progeny sample of 291 haploid segregants was obtained. The progeny strains were genotyped for standard markers. Allelic ratios and pairwise marker segregations were determined. Pairs of progeny strains that carried different alleles for the standard markers on each linkage group in turn were tested for compatibility. Strain pairs that possessed different alleles for the markers on linkage groups II, III, V, VI and VII were incompatible indicating the presence of heterokaryon-incompatible (het) genes on these linkage groups. Backcrosses to an h-cGl strain showed that two het genes were located on linkage group III and confirmed a total of six het gene differences between the h-cA and h-cGl strains.

Alleles↗
PubMed1983

The location and analysis of two heterokaryon incompatibility (het) loci in strains of Aspergillus nidulans.

The heterokaryon incompatibility system in Aspergillus nidulans has been investigated by parasexual methods. The use of complementary auxotrophs with a repeated serial transfer method or with a protoplast fusion technique has enabled heterokaryons and diploid strains to be recovered from heterokaryon incompatible combinations of strains. The effects of allelic interaction at heterokaryon incompatibility (het) loci on the morphologies of the heterokaryon and diploid colonies isolated are described. Parasexual analyses conducted among strains belonging to the heterokaryon compatibility groups, h-cGl and h-cB, and the two recombinant compatibility classes, have located the hetA and hetB genes to linkage groups V and VI respectively.

Aspergillus nidulans↗
PubMed1983

A chromosome assay method for the detection of heterokaryon incompatibility (het) genes operating between members of different heterokaryon compatibility (h-c) groups in Aspergillus nidulans.

Protoplast fusion has made possible the isolation of a diploid strain from haploid parents belonging to heterokaryon compatibility (h-c) groups Q and Gl of Aspergillus nidulans. This diploid was not fully heterokaryon compatibility tests conducted between selected pairs of parasexually derived progeny strains facilitated a chromosome assay method for the detection of heterokaryon incompatibility (het) genes. Despite the lack of segregation for the linkage group VI marker, it proved possible to locate het genes on linkage groups III, V, VI and VII. Backcross data detected five het gene differences operating between the h-cQ and h-cGl parental strains. Two het loci were located on linkage group III.

Aspergillus nidulans↗