1
|
Burmester A, Karimi S, Wetzel J, Wöstemeyer J. Complementation of a stable Met2-1 mutant of the zygomycete Absidia glauca by the corresponding wild-type allele of the mycoparasite Parasitella parasitica, transferred during infection. Microbiology (Reading) 2013; 159:1639-1648. [DOI: 10.1099/mic.0.066910-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Anke Burmester
- General Microbiology and Microbe Genetics, Friedrich-Schiller University Jena, Neugasse 24, D-07743 Jena, Germany
| | - Sedighe Karimi
- General Microbiology and Microbe Genetics, Friedrich-Schiller University Jena, Neugasse 24, D-07743 Jena, Germany
| | - Jana Wetzel
- General Microbiology and Microbe Genetics, Friedrich-Schiller University Jena, Neugasse 24, D-07743 Jena, Germany
| | - Johannes Wöstemeyer
- General Microbiology and Microbe Genetics, Friedrich-Schiller University Jena, Neugasse 24, D-07743 Jena, Germany
| |
Collapse
|
2
|
Meussen BJ, de Graaff LH, Sanders JPM, Weusthuis RA. Metabolic engineering of Rhizopus oryzae for the production of platform chemicals. Appl Microbiol Biotechnol 2012; 94:875-86. [PMID: 22526790 PMCID: PMC3339055 DOI: 10.1007/s00253-012-4033-0] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 03/14/2012] [Accepted: 03/15/2012] [Indexed: 11/28/2022]
Abstract
Rhizopus oryzae is a filamentous fungus belonging to the Zygomycetes. It is among others known for its ability to produce the sustainable platform chemicals L: -(+)-lactic acid, fumaric acid, and ethanol. During glycolysis, all fermentable carbon sources are metabolized to pyruvate and subsequently distributed over the pathways leading to the formation of these products. These platform chemicals are produced in high yields on a wide range of carbon sources. The yields are in excess of 85 % of the theoretical yield for L: -(+)-lactic acid and ethanol and over 65 % for fumaric acid. The study and optimization of the metabolic pathways involved in the production of these compounds requires well-developed metabolic engineering tools and knowledge of the genetic makeup of this organism. This review focuses on the current metabolic engineering techniques available for R. oryzae and their application on the metabolic pathways of the main fermentation products.
Collapse
Affiliation(s)
- Bas J Meussen
- Fungal Systems Biology, Laboratory of Systems and Synthetic Biology, Wageningen University, Dreijenplein 10, Wageningen, The Netherlands
| | | | | | | |
Collapse
|
3
|
Karimi S, Wetzel J, Wöstemeyer J, Burmester A. Transformation of the fungus Absidia glauca by complementation of a methionine-auxotrophic strain affected in the homoserine-acetyltransferase gene. FEBS Open Bio 2012; 2:197-201. [PMID: 23650600 PMCID: PMC3642153 DOI: 10.1016/j.fob.2012.07.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2012] [Revised: 07/06/2012] [Accepted: 07/06/2012] [Indexed: 11/30/2022] Open
Abstract
Transformation of fungi by complementation of auxotrophs is generally much more reliable than usage of antibiotic resistance markers. In order to establish such a system for the model zygomycete Absidia glauca, a stable methionine auxotrophic mutant was isolated after X-ray mutagenesis of the minus mating type and characterized at the molecular level. The mutant is disrupted in the coding region of the Met2-1 gene, encoding homoserine O-acetyltransferase. The corresponding wild type gene was cloned, sequenced and inserted into appropriate vector plasmids. Transformants are prototrophs and show restored methionine-independent growth, based on complementation by the autonomously replicating plasmids.
Collapse
Affiliation(s)
- Sedighe Karimi
- General Microbiology and Microbe Genetics, Friedrich-Schiller University Jena, Neugasse 24, D-07743 Jena, Germany
| | | | | | | |
Collapse
|
4
|
Mertens JA, Skory CD, Ibrahim AS. Plasmids for expression of heterologous proteins in Rhizopus oryzae. Arch Microbiol 2006; 186:41-50. [PMID: 16804680 DOI: 10.1007/s00203-006-0121-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Revised: 04/14/2006] [Accepted: 05/02/2006] [Indexed: 11/27/2022]
Abstract
Rhizopus oryzae has long been used for enzyme production (e.g., glucoamylase and lipase), organic acid synthesis, and various fermented food applications. In this work, we describe a set of plasmid-based expression vectors that can be used for the production of heterologous proteins in R. oryzae. Three plasmid vectors have been created using either the glucoamylase A (amyA), pyruvate decarboxylase (pdcA), or phosphoglycerate kinase (pgk1) promoters to drive expression of heterologous proteins. All three plasmids use the pdcA terminator for transcription termination, the pyrG gene for restoration of uracil prototrophy, and an ampicillin resistance gene and origin of replication for maintenance in Escherichia coli. We have expressed green fluorescent protein (GFP) and compared transcription and protein accumulation for each of the expression vectors. Accumulation of GFP transcript and protein was directly correlated with the choice of promoter with pdcA > amyA > pgk1. Transcript level appears to parallel GFP protein accumulation. Plasmid copy number had little impact on transcription or protein accumulation. These vectors should be useful for overexpression of heterologous proteins and potentially, metabolic engineering of Rhizopus strains.
Collapse
Affiliation(s)
- Jeffrey A Mertens
- Fermentation Biotechnology Research Unit, National Center for Agricultural Utilization Research, USDA, Agricultural Research Service, 1815 N. University St., Peoria, IL 61604, USA.
| | | | | |
Collapse
|
5
|
Obraztsova IN, Prados N, Holzmann K, Avalos J, Cerdá-Olmedo E. Genetic damage following introduction of DNA in Phycomyces. Fungal Genet Biol 2004; 41:168-80. [PMID: 14732263 DOI: 10.1016/j.fgb.2003.09.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Introduction of plasmids in Phycomyces blakesleeanus caused extensive changes in the exogenous DNA and in the resident genome. Plasmids with a bacterial gene for geneticin resistance under a Phycomyces promoter were either injected into immature sporangia or incubated with spheroplasts. An improved method produced about one viable spheroplast per cell. Colonies resistant to geneticin were rare and only about 0.1% of their spores grew in the presence of geneticin. The transformation frequency was very low, < or =1 transformed colony per million spheroplasts or per microg DNA. Few nuclei in the transformants contained exogenous DNA, as shown by a selective procedure that sampled single nuclei from heterokaryons. The exogenous DNA was not integrated into the genome and no stable transformants were obtained. The plasmids were replicated in the recipient cells, but their DNA sequences were modified by deletions and rearrangements and the transformed phenotype was eventually lost. The spores developed in injected sporangia were often inviable; a genetic test showed that spore death was caused by impaired nuclear proliferation and induction of lethal mutations. About one-fourth of the viable spores from injected sporangia formed abnormal colonies with obvious changes in shape, texture, or color. The abnormalities that could be investigated were due to dominant mutations. The results indicate that incoming DNA is not only attacked, but signals a situation of stress that leads to increased mutation and nuclear and cellular death.
Collapse
Affiliation(s)
- Irina N Obraztsova
- Departamento de Genética, Universidad de Sevilla, E-41012 Sevilla, Spain
| | | | | | | | | |
Collapse
|
6
|
Michielse CB, Salim K, Ragas P, Ram AFJ, Kudla B, Jarry B, Punt PJ, van den Hondel CAMJJ. Development of a system for integrative and stable transformation of the zygomycete Rhizopus oryzae by Agrobacterium-mediated DNA transfer. Mol Genet Genomics 2004; 271:499-510. [PMID: 15067540 DOI: 10.1007/s00438-004-1003-y] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Accepted: 02/27/2004] [Indexed: 10/26/2022]
Abstract
Two transformation systems, based on the use of CaCl(2)/PEG and Agrobacterium tumefaciens, respectively, were developed for the zygomycete Rhizopus oryzae. Irrespective of the selection marker used, a pyr4 marker derived from R. niveus or a dominant amdS(+) marker from Aspergillus nidulans, and irrespective of the configuration of the transforming DNA (linear or circular), the transformants obtained with the CaCl(2)/PEG transformation method were found to carry multiple copies of tandemly linked vector molecules, which failed to integrate into the genomic DNA. Furthermore, these transformants displayed low mitotic stability. In contrast, transformants obtained by Agrobacterium-mediated transformation were mitotically stable, even under non-selective conditions. Detailed analysis of these transformants revealed that the transforming DNA had integrated into the genome of R. oryzae at a single locus in independently obtained transformants. In addition, truncation of the transforming DNA was observed, resulting in the integration of the R. niveus pyr4 marker gene, but not the second gene located on the transferred DNA. Modification of the transforming DNA, resulting in partial resistance to restriction enzyme digestion, was observed in transformants obtained with the CaCl(2)/PEG transformation method, suggesting that a specific genome defence mechanism may exist in R. oryzae. It is likely that the unique mechanism used by A. tumefaciens to deliver its transferred DNA to its hosts facilitates bypass of the host defence mechanisms, thus allowing the DNA to integrate into the chromosomal genome.
Collapse
Affiliation(s)
- C B Michielse
- Fungal Genetics Group, Clusius Laboratory, Institute of Biology, Leiden University, Wassenaarseweg 64, 2333 AL, Leiden, The Netherlands.
| | | | | | | | | | | | | | | |
Collapse
|
7
|
Bartsch S, Schimek C, Wöstemeyer J. Microprojectile bombardment as a reliable method for transformation of the mucoralean fungus Absidia glauca. MYCOSCIENCE 2002. [DOI: 10.1007/s102670200031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
8
|
Wöstemeyer J, Wöstemeyer A, Burmester A, Czempinski K. Relationships between sexual processes and parasitic interactions in the host–pathogen systemAbsidia glauca–Parasitella parasitica. ACTA ACUST UNITED AC 1995. [DOI: 10.1139/b95-253] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Parasitella parasitica is a facultative parasite of many Mucorales including Absidia glauca. The infection process includes the formation of a plasmatic continuum between host and parasite, which allows the invasion of the host by nuclei of the parasite. This process gives rise to interspecies recombinants. Auxotrophic A. glauca mutants are complemented by the transfer of genes from the parasite to the host. At the molecular level, we could show that plasmid-coded genes are also transferred. The successful formation of infection structures is mating-type dependent. Parasitella parasitica exclusively infects hosts belonging to the complementary mating type. The formation of infection structures is correlated with the ability to synthesise the sex pheromone trisporic acid, which is produced in mixed cultures by compatible combinations between host and parasite. Normally, trisporic acid is formed by a cooperative biosynthesis involving both mating types. Trisporic acid seems to be involved also in mediating the recognition between P. parasitica and A. glauca. To test the hypothesis of direct hormonal correlations between sex and parasitism, we have isolated one of the key enzymes for trisporic acid synthesis, dihydromethyltrisporic acid dehydrogenase, sequenced the N-termini of some proteolytic cleavage products, and have started to isolate the corresponding gene. Key words: mycoparasitism, zygomycetes, trisporic acid, Absidia glauca, Parasitella parasitica, Mucor.
Collapse
|
9
|
Benito EP, Campuzano V, Lŏpez-Matas MA, De Vicente JI, Eslava AP. Isolation, characterization and transformation, by autonomous replication, of Mucor circinelloides OMPdecase-deficient mutants. MOLECULAR & GENERAL GENETICS : MGG 1995; 248:126-35. [PMID: 7651335 DOI: 10.1007/bf02190793] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Pyrimidine auxotrophs of Mucor circinelloides were isolated after mutagenesis with nitrosoguanidine and selected for resistance to 5-fluoroorotate. These mutants were genetically and biochemically characterized and found to be deficient either in orotidine-5'-monophosphate decarboxylase (OMPdecase) activity or in orotate phosphoribosyl transferase (OPRTase) activity. Different circular DNA molecules containing the homologous pyrG gene were used to transform a representative OMPdecase-deficient strain to uracil prototrophy. Southern analysis, as well as mitotic stability analysis of the transformants, showed that the transforming DNA is always maintained extrachromosomally. The smallest fragment tested that retained both the capacity to complement the pyrG4 mutation and the ability to be maintained extrachromosomally when cloned in a suitable vector is a 1.85 kb M. circinelloides genomic DNA fragment. This fragment consists of the pyrG coding region flanked by 606 nucleotides at the 5' and 330 nucleotides at the 3' ends, respectively. Sequence analysis reveals that it does not share any element in common with another M. circinelloides genomic DNA fragment which also promotes autonomous replication in this organism, except those related to transcription. Furthermore, it differs from elements which have been shown to be involved in autonomous replication in other fungal systems. An equivalent plasmid harbouring the heterologous Phycomyces blakesleeanus pyrG gene yielded lower transformation rates, but the transforming DNA was also maintained extrachromosomally. Our results suggest that autonomous replication in M. circinelloides may be driven by elements normally present in nuclear coding genes.
Collapse
Affiliation(s)
- E P Benito
- Dpto. de Microbiología y Genética, Universidad de Salamanca, Spain
| | | | | | | | | |
Collapse
|
10
|
Lemke PA. The Thom Award address. Industrial mycology and the new genetics. JOURNAL OF INDUSTRIAL MICROBIOLOGY 1995; 14:355-64. [PMID: 7612213 DOI: 10.1007/bf01569951] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The genetic investigation of fungi has been extended substantially by DNA-mediated transformation, providing a supplement to more conventional genetic approaches based upon sexual and parasexual processes. Initial transformation studies with the yeast Saccharomyces cerevisiae provided the model for transformation systems in other fungi with regard to methodology, vector construction and selection strategies. There are, however, certain differences between S. cerevisiae and filamentous fungi with regard to type of genomic insertion and the availability of shuttle vectors. Single-site linked insertions are common in yeast due to the high level of homology required for recombination between vectored and genomic sequences, whereas mycelial fungi often show a high frequency of heterologous and unlinked insertions, often in the form of random and multiple-site integrations. While extrachromosomally-maintained or replicative vectors are readily available for use with yeasts, such vectors have been difficult to construct for use with filamentous fungi. The development of vectors for replicative transformation with these fungi awaits further study. It is proposed that replicative vectors may be inherently less efficient for use with mycelial fungi relative to yeasts, since the mycelium, as an extended and semicontinuous network of cells, may delimit an adequate diffusion of the vector carrying the selectable gene, thus leading to a high frequency of abortive or unstable transformants.
Collapse
Affiliation(s)
- P A Lemke
- Department of Botany and Microbiology, Auburn University, AL 36849-5407, USA
| |
Collapse
|
11
|
Burmester A. Analysis of the gene for the elongation factor 1 alpha from the zygomycete Absidia glauca. Use of the promoter region for constructions of transformation vectors. Microbiol Res 1995; 150:63-70. [PMID: 7735720 DOI: 10.1016/s0944-5013(11)80035-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The complete genomic DNA sequence was determined for one of the gene for the elongation factor 1 alpha (TEF), isolated from the zygomycete Absidia glauca. Sequence comparison with TEF genes from other fungi show the highest similarity to TEF-genes of the closely related zygomycete Mucor racemosus (Sundstrom et al. 1987). Southern-blot analysis of genomic DNA from A. glauca with the TEF gene reveals six chromosomal copies in the genome. In transformation experiments of A. glauca, vector constructions were used which allow targeting of one of the TEF loci. Several transformants of A. glauca were analyzed at the DNA level. In most cases, rearranged forms of autonomously replicated plasmids could be found in these isolates. However, some transformants show a different restriction pattern of the TEF loci if compared with the parental strains. From Southern-blot data it could be concluded that in one case the rearrangement lies downstream of one TEF locus. In a second case genetic parts following the 3'-end of the TEF gene are moved towards the 5'-end of the gene.
Collapse
Affiliation(s)
- A Burmester
- Institut für Mikrobiologie, Friedrich-Schiller-Universität Jena, Germany
| |
Collapse
|
12
|
Moreno MA, Pascual C, Gibello A, Ferrer S, Bos CJ, Debets AJ, Suárez G. Transformation of Aspergillus parasiticus using autonomously replicating plasmids from Aspergillus nidulans. FEMS Microbiol Lett 1994; 124:35-41. [PMID: 8001767 DOI: 10.1111/j.1574-6968.1994.tb07258.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
A genetic transformation system for the aflatoxin-producing fungus Aspergillus parasiticus using two autonomously replicating plasmids from A. nidulans (ARp1 and pDHG25) is reported. Transformation frequencies using the plasmid pDHG25 were from 5 x 10(2) to 2.5 x 10(4) transformants per 10(6) viable protoplasts and microgram DNA. The stability of the plasmids in the transformants was also studied. This transformation system offers a new opportunity to clone genes related to aflatoxin production using appropriate aflatoxin-defective mutants.
Collapse
Affiliation(s)
- M A Moreno
- Department de Patología Animal I, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain
| | | | | | | | | | | | | |
Collapse
|
13
|
Coleman MJ, McHale MT, Arnau J, Watson A, Oliver RP. Cloning and characterisation of telomeric DNA from Cladosporium fulvum. Gene X 1993; 132:67-73. [PMID: 8104848 DOI: 10.1016/0378-1119(93)90515-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The molecular cloning of DNA from the telomere of one chromosome of Cladosporium fulvum, a fungal pathogen of tomato, is described. The telomeric DNA exhibits tandem repeats of the sequence TTAGGG running 5' to 3' toward the chromosome end. At least 16 tracts of TTAGGG repeats are present in the C. fulvum genome. All such tracts are telomeric, and all chromosome-sized DNAs separated by pulsed-field gel electrophoresis exhibit the repeats. It is probable that tracts of these repeats are present at all chromosome termini. The cloned telomeric DNA exhibits 19 copies of the TTAGGG hexanucleotide motif, and evidence is presented indicating that all tracts of TTAGGG repeats are quite short. Telomere-linked restriction-fragment length polymorphisms between races of C. fulvum have been detected, and groupings based on these polymorphisms are consistent with those determined previously. Sub-telomeric DNA, centromere proximal to the cloned telomeric DNA, contains sequences reiterated many times in the genome; some of these repeats are at non-terminal locations. Partial sequence analysis indicates an absence of homology with the sub-telomeric DNA of other organisms.
Collapse
Affiliation(s)
- M J Coleman
- Norwich Molecular Plant Pathology Group, School of Biological Sciences, University of East Anglia, UK
| | | | | | | | | |
Collapse
|
14
|
Arnau J, Strøman P. Gene replacement and ectopic integration in the zygomycete Mucor circinelloides. Curr Genet 1993; 23:542-6. [PMID: 8319313 DOI: 10.1007/bf00312649] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Transformation of Mucor circinelloides with plasmid pTL42 led to the identification of different integrative events. Analysis of eight transformed strains allowed the detection of three classes of transformants: integrative types derived from either homologous (exclusively at the leuA locus) or heterologous recombination and a class which originated by gene replacement. No autonomous replication of the vector was observed.
Collapse
Affiliation(s)
- J Arnau
- Department of Physiology, Carlsberg Laboratory, Copenhagen, Denmark
| | | |
Collapse
|
15
|
Arnau J, Oliver RP. Inheritance and alteration of transforming DNA during an induced parasexual cycle in the imperfect fungus Cladosporium fulvum. Curr Genet 1993; 23:508-11. [PMID: 8319310 DOI: 10.1007/bf00312643] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Protoplasts of a pAN7-1-transformed isolate of Cladosporium fulvum race 4, harbouring a tandem duplication of the vector, and an untransformed race 5 isolate were fused, without selection for the presence of vector sequences. Fusion products were allowed to haploidize spontaneously. The inheritance of pAN7-1 sequences and the expression of the hph gene was studied in 85 progeny. A very high proportion (80%) of the progeny contained vector sequences and 70% of the progeny were resistant to hygromycin. Inactivation of the hph gene occurred in eight progeny. Rearrangement of vector sequences can account for the inactivation: there is no evidence for any RIP-like mechanism. A number of novel bands were observed.
Collapse
Affiliation(s)
- J Arnau
- School of Biological Sciences, University of East Anglia, Norwich, UK
| | | |
Collapse
|
16
|
Kellner M, Burmester A, Wöstemeyer A, Wöstemeyer J. Transfer of genetic information from the mycoparasite Parasitella parasitica to its host Absidia glauca. Curr Genet 1993; 23:334-7. [PMID: 8467531 DOI: 10.1007/bf00310895] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The infection of the model organism Absidia glauca by P. parasitica is accompanied by the fusion of both mycelia. By two lines of evidence we were able to show that this process is associated with the transfer of genes. First, auxotrophically labelled A. glauca mutants are efficiently complemented as a consequence of transfer of the parasite's genetic material. Second, for a plasmid-coded dominant marker (neomycin resistance), which is expressed in either organism, we proved the presence of plasmid DNA in recombinant recipients by molecular analysis at the DNA level. We propose the term para-recombinants for describing recombinant inter-generic chimaerae, which are generated as a consequence of mycoparasitism.
Collapse
Affiliation(s)
- M Kellner
- Institut für Genbiologische Forschung, Berlin, Germany
| | | | | | | |
Collapse
|