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

Trichoderma hamatum and Its Benefits

Trichoderma hamatum (Bonord.) Bainier (T. hamatum) belongs to Hypocreaceae family, Trichoderma genus. Trichoderma spp. are prominently known for their biocontrol activities and plant growth promotion. Hence, T. hamatum also possess several beneficial activities, such as antimicrobial activity, antioxidant activity, insecticidal activity, herbicidal activity, and plant growth promotion; in addition, it holds several other beneficial properties, such as resistance to dichlorodiphenyltrichloroethane (DDT) and degradation of DDT by certain enzymes and production of certain polysaccharide-degrading enzymes. Hence, the current review discusses the beneficial properties of T. hamatum and describes the gaps that need to be further considered in future studies, such as T. hamatum's potentiality against human pathogens and, in contrast, its role as an opportunistic human pathogen. Moreover, there is a need for substantial study on its antiviral and antioxidant activities.

Comparative studies of differential expression of chitinolytic enzymes encoded by chiA, chiB, chiC and nagA genes in Aspergillus nidulans

N-Acetyl-D-glucosamine, chito-oligomers and carbon starvation regulated chiA, chiB, and nagA gene expressions in Aspergillus nidulans cultures. The gene expression patterns of the main extracellular endochitinase ChiB and the N-acetyl-beta-D-glucosaminidase NagA were similar, and the ChiB-NagA enzyme system may play a morphological and/or nutritional role during autolysis. Alterations in the levels of reactive oxygen species or in the glutathione-glutathione disulfide redox balance, characteristic physiological changes developing in ageing and autolyzing fungal cultures, did not affect the regulation of either the growth-related chiA or the autolysis-coupled chiB genes although both of them were down-regulated under diamide stress. The transcription of the chiC gene with unknown physiological function was repressed by increased intracellular superoxide concentration.

Identification of novel Trichoderma hamatum genes expressed during mycoparasitism using subtractive hybridisation

Subtractive hybridisation was used to target novel genes involved in the mycoparasitic interaction of the biocontrol agent Trichoderma hamatum with the phytopathogen Sclerotinia sclerotiorum. Nineteen novel T. hamatum genes were identified that showed increased expression during mycoparasitism compared to a T. hamatum control. Sequence analysis revealed some cDNA fragments had similarity to known fungal or bacterial genes whereas others had no similarity to any genes previously described. Only one of the novel genes has been characterised in another Trichoderma species, the Trichoderma reesei hex1gene. The proteins encoded by the novel genes included three monooxygenases, a metalloendopeptidase, a gluconate dehydrogenase, an endonuclease and a proton ATPase.

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).

Expression of cmg1, an exo-beta-1,3-glucanase gene from Coniothyrium minitans, increases during sclerotial parasitism

During sclerotial infection of Sclerotinia sclerotiorum the mycoparasite Coniothyrium minitans penetrates through the host cell wall, which contains beta-1,3-glucan as its major component. A PCR-based strategy was used to clone a beta-1,3-glucanase-encoding gene, designated cmg1, from a cDNA library of the fungus. The nucleotide and deduced amino acid sequences of this gene showed high levels of similarity to the sequences of other fungal exo-beta-1,3-glucanase genes. The calculated molecular mass of the deduced protein (without the predicted 24-amino-acid N-terminal secretion signal peptide) was 83,346 Da, and the estimated pI was 4.73. Saccharomyces cerevisiae INVSc1 expressing the cmg1 gene secreted a approximately 100-kDa beta-1,3-glucanase enzyme (as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) into the culture medium. N-terminal sequence analysis of the purified recombinant enzyme revealed that the secreted enzyme starts at Ala-32, seven amino acids downstream from the predicted signal peptidase cleavage site. The purified recombinant glucanase inhibited in vitro mycelial growth of S. sclerotiorum by 35 and 85% at concentrations of 300 and 600 microg x ml(-1), respectively. A single copy of the cmg1 gene is present in the genome of C. minitans. Northern analyses indicated increases in the transcript levels of cmg1 due to both carbon starvation and the presence of ground sclerotia of S. sclerotiorum; only slight repression was observed in the presence of 2% glucose. Expression of cmg1 increased during parasitic interaction with S. sclerotiorum.

Chitinolytic enzymes: an exploration

Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications. Particularly, chitinases are used in agriculture to control plant pathogens. Chitinases and chitooligomers produced by enzymatic hydrolysis of chitin can also be used in human health care. The success in employing chitinases for different aspects depends on the supply of highly active preparations at reasonable cost. Therefore, the understanding of biochemistry and genetics of chitinolytic enzymes, their phylogenetic relationships and methods of estimation will make them more useful in a variety of processes in near future.

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.

Expression of two major chitinase genes of Trichoderma atroviride (T. harzianum P1) is triggered by different regulatory signals

Regulation of the expression of the two major chitinase genes, ech42 (encoding the CHIT42 endochitinase) and nag1 (encoding the CHIT73 N-acetyl-beta-D-glucosaminidase), of the chitinolytic system of the mycoparasitic biocontrol fungus Trichoderma atroviride (= Trichoderma harzianum P1) was investigated by using a reporter system based on the Aspergillus niger glucose oxidase. Strains harboring fusions of the ech42 or nag1 5' upstream noncoding sequences with the A. niger goxA gene displayed a glucose oxidase activity pattern that was consistent under various conditions with expression of the native ech42 and nag1 genes, as assayed by Northern analysis. The expression product of goxA in the mutants was completely secreted into the medium, detectable on Western blots, and quantifiable by enzyme-linked immunosorbent assay. nag1 gene expression was triggered during growth on fungal (Botrytis cinerea) cell walls and on the chitin degradation product N-acetylglucosamine. N-Acetylglucosamine, di-N-acetylchitobiose, or tri-N-acetylchitotriose also induced nag1 gene expression when added to mycelia pregrown on different carbon sources. ech42 expression was also observed during growth on fungal cell walls but, in contrast, was not triggered by addition of chitooligomers to pregrown mycelia. Significant ech42 expression was observed after prolonged carbon starvation, independent of the use of glucose or glycerol as a carbon source, suggesting that relief of carbon catabolite repression was not involved in induction during starvation. In addition, ech42 gene transcription was triggered by physiological stress, such as low temperature, high osmotic pressure, or the addition of ethanol. Four copies of a putative stress response element (CCCCT) were found in the ech42 promoter.