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- Author or Editor: L. Manczinger x
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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.
Losses due to plant diseases may be as high as 10-20% of the total worldwide food production every year, resulting in economic losses amounting to many billions of dollars and diminished food supplies. Chemical control involves the use of chemical pesticides to eradicate or reduce the populations of pathogens or to protect the plants from infection by pathogens. For some diseases chemical control is very effective, but it is often non-specific in its effects, killing beneficial organisms as well as pathogens, and it may have undesirable health, safety, and environmental risks. Biological control involves the use of one or more biological organisms to control the pathogens or diseases. Biological control is more specialized and uses specific microorganisms that attack or interfere with the pathogens. The members of the genus Trichoderma are very promising against soil-born plant parasitic fungi. These filamentous fungi are very widespread in nature, with high population densities in soils and plant litters [1]. They are saprophytic, quickly growing and easy to culture and they can produce large amounts of conidia with long lifetime.
Eleven cold-tolerant Trichoderma isolates were screened for the production of proteolytic activities at 10 °C. Based on the activity profiles determined with paranitroanilide substrates at 5 °C, strain T221 identified as Trichoderma atroviride was selected for further investigations. The culture broth of the strain grown at 10 °C in casein-containing culture medium was concentrated by lyophilization and subjected to gel filtration, which was followed by chromatofocusing of the fraction showing the highest activity on N -benzoyl-Phe-Val-Arg-paranitroanilide. The purified enzyme had a molecular weight of 24 kDa, an isoelectric point of 7.3 and a pH optimum of 6.2. The temperature optimum of 25 °C and the low thermal stability suggested that it is a true cold-adapted enzyme. Substrate specificity data indicate that the enzyme is a proteinase with a preference for Arg or Lys at the P1 position. The effect of proteinase inhibitors suggests that the enzyme has a binding pocket similar to the one present in trypsin.
Peptaibols and the related peptaibiotics are linear, amphipathic polypeptides. More than 300 of these secondary metabolites have been described to date. These compounds are composed of 5-20 amino acids and are generally produced in microheterogeneous mixtures. Peptaibols and peptaibiotics with unusual amino acid content are the result of non-ribosomal biosynthesis. Large multifunctional enzymes known as peptide synthetases assemble these molecules by the multiple carrier thiotemplate mechanism from a remarkable range of precursors, which can be N-methylated, acylated or reduced. Peptaibols and peptaibiotics show interesting physico-chemical and biological properties including the formation of pores in bilayer lipid membranes, as well as antibacterial, antifungal, occasionally antiviral activities, and may elicit plant resistance. The three-dimensional structure of peptaibols and peptaibiotics is characterized predominantly by one type of the helical motifs a-helix, 310-helix and b-bend ribbon spiral. The aim of this review is to summarize the data available about the biosynthesis, biological activity and conformational properties of peptaibols and peptaibiotics described from Trichoderma species.
Cellulolytic, xylanolytic, chitinolytic and b-1,3-glucanolytic enzyme systems of species belonging to the filamentous fungal genus Trichoderma have been investigated in details and are well characterised. The ability of Trichoderma strains to produce extracellular proteases has also been known for a long time, however, the proteolytic enzyme system is relatively unknown in this genus. Fortunately, in the recent years more and more attention is focused on the research in this field. The role of Trichoderma proteases in the biological control of plant pathogenic fungi and nematodes has been demonstrated, and it is also suspected that they may be important for the competitive saprophytic ability of green mould isolates and may represent potential virulence factors of Trichoderma strains as emerging fungal pathogens of clinical importance. The aim of this review is to summarize the information available about the extracellular proteases of Trichoderma. Numerous studies are available about the extracellular proteolytic enzyme profiles of Trichoderma strains and about the effect of abiotic environmental factors on protease activities. A number of protease enzymes have been purified to homogeneity and some protease encoding genes have been cloned and characterized. These results will be reviewed and the role of Trichoderma proteases in biological control as well as their advantages and disadvantages in biotechnology will be discussed.
Cefditoren is the active form of cefditoren pivoxil, a new, broad-spectrum oral cephalosporin with strong in vitro activity against penicillin-susceptible and resistant Streptococcus pneumoniae. In this study, the minimum inhibitory concentrations (MICs) of cefditoren were determined for a special selection of S. pneumoniae isolates known to be susceptible, moderately susceptible or fully resistant to penicillin; these isolates originated from the lower respiratory tract of adults with pneumonia or the upper respiratory tract of children with or without symptoms of infection. Some of this latter group of isolates exhibited extremely high MICs to penicillin (³32 mg/l), whereas the MICs of cefditoren did not exceed 2 mg/l. The MIC50 and MIC90 of cefditoren proved to be 0.25 and 1.0 mg/l, respectively, with a range of MICs £0.015-2.0 mg/l for all the tested S. pneumoniae isolates. Its good activity suggests that cefditoren is expected to be a potent drug in infections caused by penicillin-resistant and multidrug-resistant S. pneumoniae.
Species belonging to the filamentous fungal genus Trichoderma are well known as potential candidates for the biological control of plant pathogenic fungi and as cellulase producers of biotechnological importance. Several data were published in the last decade also about the clinical importance of this genus, indicating that Trichoderma strains may be potential opportunistic pathogens in immunocompromised patients. However, there is a lack of information about the potential virulence factors of clinical Trichoderma strains. This study was designed to examine the extracellular proteolytic enzymes of six clinical T. longibrachiatum isolates. Supernatants from induced liquid cultures of the examined strains were screened for proteolytic enzyme activities with 11 different chromogenic p-nitroaniline substrates. The production of trypsin-like, chymotrypsin-like and chymoelastase-like protease activities cleaving N-Benzoyl-L-Phe-L-Val-L-Arg-p-nitroanilide, N-Succinyl-L-Ala-L-Ala-L-Pro-L-Phe-p-nitroanilide,and N-Succinyl-L- Ala-L-Ala-L-Pro-L-Leu-p-nitroanilide, respectively, was common among the strains examined. Separation of trypsin- and chymotrypsin-like activities by column chromatography revealed, that both systems are complex consisting of several isoenzymes. The pH-dependence of these two protease systems was also studied. Based on the results, the different isoenzymes seem to have different optimal pH values. Extracellular proteolytic enzymes may be involved in the pathogenecity of Trichoderma strains as facultative human pathogens.
Potential virulence factors of 9 saprophytic and 12 clinical Trichoderma longibrachiatum strains were examined in the present study, in order to compare their capacity to cause infection in humans. All of the strains were able to grow at temperatures up to 40 °C and at pH values ranging from 2.0 to 9.0. Carbon and nitrogen source utilization experiments revealed that all of the strains were able to utilize a series of basic amino acids both as sole carbon and nitrogen sources. The MIC values of the tested antifungal drugs were found to be 0.016-8 µg/ml for amphotericin B, 64-256 µg/ml for fluconazole, 0.5-32 µg/ml for itraconazole and 0.008-1 µg/ml for ketoconazole in the case of the examinedis olates. Metabolites of the strains inhibited the growth of different bacteria, furthermore, compounds produced by three clinical isolates reduced the motility of boar spermatozoa, indicating their toxicity to mammalian cells as well. On the whole, there were no significant differences in the examined features between strains derived from clinical or soil samples. The question, however, whether all environmental Trichoderma longibrachiatum strains have the capacity to cause infections or not, remains still unanswered.
