Transformation of Trichoderma species with dominant selectable markers

Karyotyping of Candida albicans and Candida glabrata isolates from recurrent vaginal infections by pulsed-field gel electrophoresis

In the present study, 16 women with recurrent vulvovaginal candidiasis (RVVC) due to Candida albicans and Candida (Torulopsis) glabrata were followed for a period of 4 to 12 months, and 36 vaginal isolates were evaluated by pulsed-field gel electrophoresis (PFGE). Eleven women were infected by C. albicans and 5 by C. glabrata. Three electrophoretic karyotypes of C. albicans and 3 of C. glabrata were identified throughout the follow-up. All patients but one was infected with the same karyotype of C. albicans or C. glabrata during the follow-up period. Two different karyotypes of C. glabrata were identified in one patient in the course of 12 months. The results confirmed the diversity of the karyotypes of C. albicans and C. glabrata causing vulvovaginitis, and demonstrated the persistence of colonization with the same strain over different periods of time despite therapy (15/16 women).

Pinto F, Fungaro MHP. Transformation of the entomopathogenic fungusMetarhizium flavovirideto high resistance to benomyl

A Brazilian isolate of Metarhizium flavoviride, which has been developed as a biocontrol agent against the grasshopper Rhammatocerus schistocercoides, was stably transformed to be resistant to benomyl (beta-tubulin gene). Highly resistant transformants were obtained which grew in benomyl concentrations greater than 30 times (200 µg mL-1) the concentration that inhibits wild type proliferation. These transformants were mitotically stable after 20 successive transfers on non-selective media. No significant differences in conidia yield were observed between stably transformed strains and wild type (CG423). Chymoelastase (Pr1) secretion was greater in some transformants than in the wild type. In the presence of benomyl, appressoria differentiation occurred at similar rates in CG423 and transformants. However, the percentage of conidial germination in the transformants was higher than in the wild type, indicating the potential use of these transformants along with benomyl. Additionally, the resistance levels of the transformants observed in the present study demonstrate the potential use of these transformants for assessing the persistence of a particular isolate in fields without this fungicide.Key words: Metarhizium flavoviride, genetic transformation, benomyl resistance, biocontrol.

Biological control of agricultural pests by filamentous fungi

Agricultural use of chemical pesticides has polluted the environment and resulted in resistance among the target organisms. The chemical strategies of pest control are dangerous to both the nontarget organisms in natural habitats and human health. Biological control is an attractive less dangerous possibility for controlling plant pathogens.Some methods of biological control are becoming now commercially available against plant parasitic fungi, nematods and insects. Among filamentous fungi many candidates with biocontrol potential can be found. Fungal biocontrol agents are less effective and reliable than the synthetic pesticides therefore their use in the agricultural practice requires genetic improvement.

Transformation with green fluorescent protein of Trichoderma harzianum 1051, a strain with biocontrol activity against Crinipellis perniciosa, the agent of witches'-broom disease of cocoa

A plasmid vector for fungal expression of an enhanced, red-shifted variant of the Aequoria victoriae green fluorescent protein was constructed by fusion of the EGFP gene to the highly expressed Aspergillus nidulans gpd promoter and the A. nidulans trpC terminator. This construction was introduced by cotransformation, using benomyl selection, into Trichoderma harzianum strain 1051, a strain being evaluated for the biological control of witches'-broom disease of cocoa caused by Crinipellis perniciosa. Epifluorescence microscopy was used to monitor germination and attachment of stable transformant conidia on the surface of C. perniciosa hyphae.

Transformation of the entomopathogenic fungi, paecilomyces fumosoroseus and paecilomyces lilacinus (deuteromycotina: hyphomycetes) to benomyl resistence

The entomopathogenic fungi Paecilomyces fumosoroseus and P. lilacinus have been transformed to resistance to the fungicide benomyl by a polyethylene glycol (PEG)-mediated procedure using a mutant <FONT FACE="Symbol">b</font>-tubulin gene from Neurospora crassa carried on plasmid pBT6. Benomyl-resistant transformants of P. lilacinus were obtained that could tolerate greater than 30 µg/ml benomyl and P. fumosoroseus transformants were obtained that could tolerate 20 µg/ml benomyl. Following 5 serial passages of transformants on benomyl-containing media and 5 serial passages on non-selective media, 100% of P. lilacinus transformants were found to be mitotically stable by a conidial germination test. In contrast, only 4 out of 9 transformants of P. fumosoroseus were mitotically stable. Southern blot analysis of genomic DNA from both species suggested that the mechanism of transformation in all transformants was by gene replacement of the <FONT FACE="Symbol">b</font>-tubulin allele. Non-homologous vector sequences were not detectable in the genomes of transformants.

Homologous transformation of Trichoderma hamatum with an endochitinase encoding gene, resulting in increased levels of chitinase activity

A 42-kDa endochitinase encoding gene, Tham-ch, was cloned by screening the genomic library of Trichoderma hamatum strain Tam-61 with a PCR-amplified chitinase sequence from the same fungus. Tham-ch with its own regulatory sequences was reintroduced into the host strain. The integration of the transforming construct was stable only in one copy. Homologous integration occurred in nine transformants, while non-homologous integration was detected in one transformant. All but one transformant expressed higher levels of chitinase activity in comparison to the wild-type recipient strain; the maximum level of increase was 5-fold. Duplicating the copy number of the highly conserved approximately 42-kDa endochitinase encoding gene appears to be one potential means by which the biocontrol capability of the Trichoderma species might be improved.

Biological and molecular characterisation of potential biocontrol strains of Trichoderma

Thirty-four strains of seven species of Trichoderma isolated from various fungal sources were compared for direct mycoparasitic activity (MPA), chitinase production and antibiotic activity (ANA) in order to choose the most appropriate partners for a strain-breeding programme. Within species genetic differences were also assesses in T. hamatum, T. harzianum and T. viride by means of random amplification of polymorphic DNA (RAPD). Endochitinase activities of the Trichoderma strains ranged between 20.4 and 1264.5 units/g dry weight of mycelium. The correlation between MPA and chitinase activity was not unambiguous and no correlation existed between MPA and ANA. The RAPD patterns of T. viride strains were highly variable, while isolates of T. harzianum proved to be more uniform; T. hamatum revealed remarkable intraspecific divergence. All these three comprised certain pairs of strains that are promising participants of a strain-improving programme, since their strong genetic affinities offer good changes for combining their contrasted biocontrol traits.

Presence of a P1 bacteriophage sequence in transforming plasmids of Pleurotus ostreatus

Replicative plasmids pP01 and pP02, recovered from Pleurotus ostreatus transformants, contain an insert of bacteriophage origin. These plasmids have been amplified by the polymerase chain reaction (PCR) and have been shown to represent a low-grade component in the initial preparation of the vector pAN7-1. The pP01 and pP02 plasmids share an insert (P01A) of virtual identity with a SmaI-BamHI genomic fragment of P 1 bacteriophage and retain remnants of a polylinker at the 5' end of this fragment. Such an insert undoubtedly represents an in vitro-generated event and did not arise, as suggested previously, by recombination of pAN7-1 with the P. ostreatus genome. The P. ostreatus transformants, however, do select for the minority pP0 plasmid, apparently recognizing the P01A insert as a heterologous or surrogate replicon.

Transformation of Trichoderma reesei based on hygromycin B resistance using homologous expression signals

Trichoderma reesei was transformed to hygromycin B resistance using a novel vector, which contains the E. coli hygromycin B phosphotransferase gene (hph) fused between promoter and terminator elements of the homologous Trichoderma pki1 (coding for pyruvate kinase) and cbh2 (coding for cellobiohydrolase II) genes, respectively. Transformation frequencies of over 1,800--2,500 transformants/micrograms DNA were obtained, which is a 15--20-fold increase over that with pAN7-1, which contains hph between A. nidulans expression signals. Mitotically-stable transformants contained the hph gene and the regulatory sequences of the pki1 promoter and the cbh2 terminator integrated into the genome. Evidence for preferentially ectopic integration is given.

Development of a transformation system for Trichoderma longibrachiatum and its use for constructing multicopy transformants for the egl1 gene

An efficient transformation system for the fungus Trichoderma longibrachiatum has been developed. Transformation was obtained both by electroporation and polyethyleneglycol treatment, using a plasmid carrying the Escherichia coli hygromycin B phosphotransferase gene as a dominant selectable marker. The transformation frequency was 0.5 to 5 transformants/micrograms plasmid DNA. Transformation normally occurred by tandem integration of the transforming DNA. A high percentage of the transformants were mitotically unstable. The efficiency of co-transformation was very high (around 90%), and several co-transformants containing multiple copies of the egl1 gene encoding a beta-(1,4)-endoglucanase were obtained. Some of them secrete increased levels of endoglucanase to the culture medium. In addition, the E. coli lacZ gene was expressed in an active form under control of the Aspergillus nidulans gpdA gene promoter.

Cloning of an Aspergillus niger invertase gene by expression in Trichoderma reesei

The filamentous fungus Aspergillus niger produces two glycosylated forms of the sucrose-hydrolysing enzyme, invertase. In contrast, some Trichoderma species lack invertase and are unable to utilise sucrose as a sole carbon source. Using an A. niger genomic library constructed in a cosmid vector containing the ura5 gene of Podospora anserina as a selectable marker, and the T. reesei ura5- strain as a sucrose-minus recipient strain, an A. niger invertase gene (suc1) has been cloned by a sib selection procedure. PAGE and enzyme analysis confirmed that transformants had acquired invertase activity. The cloned gene contained DNA sequences which were complementary to the amino-acid sequences of tryptic peptides found in invertase purified from A. niger. The suc1 invertase gene can be used as a dominant selectable marker for the transformation of Trichoderma strains.