Chitin, the most abundant aminopolysaccharide in nature, is a rigid and resistant structural component that contributes to the mechanical strength of chitin-containing organisms. Chemically, it is a linear cationic heteropolysaccharide composed of N-acetyl-D-glucosamine and Dglucosamine units. The enzymatic degradation of chitin is performed by a chitinolytic system with synergistic and consecutive action. Diverse organisms (containing chitin or not) produce a great variety of chitinolytic enzymes with different specificities and catalytic properties. Their physiological roles involve nutrition, parasitism, chitin recycling, morphogenesis, and/or defense. Microorganisms, as the main environmental chitin degraders, constitute a very important natural source of chitinolytic enzymes. Nowadays, the most used method for pest and plant diseases control is the utilization of chemical agents, causative of significant environmental pollution. Social concern has generated the search for alternative control systems (i.e., biological control), which contribute to the generation of sustainable agricultural development. Interactions among the different organisms are the natural bases of biological control. Interest in chitinolytic enzymes in the field of biological control has arisen due to their possible involvement in antagonistic activity against pathogenic chitin-containing organisms. The absence of chitin in plants and vertebrate animals allows the consideration of safe and selective "target" molecules for control of chitin-containing pathogenic organisms. Fungi show appropriate characteristics as potential biological control agents of insects, fungi, and nematodes due to the production of fungal enzymes with antagonistic action. The antagonistic interactions between fungi and plant nematode parasites are among the most studied experimental models because of the high economic relevance. Fungi which target nematodes are known as nematophagous fungi. The nematode egg is the only structural element where the presence of chitin has been demonstrated. In spite of being one of the most resistant biological structures, eggs are susceptible to being attacked by egg-parasitic fungi. A combination of physical and chemical phenomena result in their complete destruction. The contribution of fungal chitinases to the in vitro rupture of the eggshell confirms their role as a pathogenic factor. Chitinases have been produced by traditional fermentation methods, which have been improved by optimizing the culture conditions for industrial processes. Although wild-type microorganisms constitute an alternative source of chitinolytic enzymes, the advances in molecular biology are allowing the genetic transformation of fungi to obtain strains with high capability as biocontrol agents. Simultaneously, a better understanding of rhizosphere interactions, additional to the discovery of new molecular biology tools, will allow the choosing of better alternatives for the biological control of nematodes in order to achieve an integrated management of t...
Biological control of nematodes by fungi is a promising field of application at large scale. Nematode egg is probably the most resistant stage in the nematode life-cycle, however they are susceptible to colonization and destruction by fungal egg-parasites. Fungal extra-cellular enzymes are able to degrade the main chemical constituents of nematode eggshell and at least they are partly responsible for fungal penetration and/or digestion of the internal tissues. Paecilomyces lilacinus was reported as an ovicidal fungus of Toxocara canis eggs in vitro, a parasite of dogs causing toxocarosis. Two wild-type P. lilacinus LPSC # 876 and LPSC # 44 strains, isolated from soil in the main park in the city of La Plata and an agricultural field, respectively, in Argentina, showed antagonism onto T. canis eggs. Besides from the isolation source, both strains showed similar hydrolytic profiles activities, ovicidal effect, and grew well on chitin agar, although no chitinolytic activity was detected. Nevertheless, both strains displayed proteolytic and chitinolytic activities in liquid cultures, with maximum values at 14 days of growth. Variable enzyme activities were observed on carboxymethylcellulose and starch agars, whereas the lipolytic activity was poor in both. Percentage of infected T. canis eggs was found 65.6% and 63.2% for P. lilacinus LPSC # 876 and # 44 strains respectively. Our results a priori indicate that P. lilacinus LPSC # 876 shows suitable characteristics as a potential agent for biocontrol of T. canis.
Chagas is a complex socio-environmental health problem with a direct and indirect impact on millions of people all over the world (Coura and Viñas 2010). The degree of advancement in scientific knowledge about the biological, medical, and
The use of multispecies bacterial bio-inputs is a promising strategy for sustainable crop production over the use of single-species inoculants. Studies of the use of multispecies bio-inputs in horticultural crops are scarce, not only on the growth-promoting effects of each bacterium within the formulation, but also on their compatibility and persistence in the root environment. In this work, we described that a multispecies bacterial bio-input made up of Azospirillum argentinense Az39, Gluconacetobacter diazotrophicus PAL-5, Pseudomonas protegens Pf-5 and Bacillus sp. Dm-B10 improved lettuce plant growth more effectively than when these strains were inoculated as single-species bio-inputs. Bacteria persisted together (were compatible) and also colonized seedling roots of lettuce plants grown in controlled conditions. Interestingly, colonization was highly related to an early and enhanced growth of seedlings grown in the nursery. A similar effect on plant growth was found in lettuce plants in a commercial greenhouse production in the peri-urban area of La Plata City, Buenos Aires, Argentina. To our knowledge, this is the first study demonstrating that a synthetic mixture of bacteria can colonize and persist on lettuce plants, and also showing their synergistic beneficial effect both in the nursery greenhouse as well as the commercial production farm.
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