Abstract
Studies with streptomycetes in biocontrol programs and plant growth promotion are presented as technological alternatives for environmental sustainable production. This work has the objective of characterizing six isolates of streptomycetes aiming the production of extracellular enzymes, indole acetic acid, capacity for phosphate solubilization, root colonization and growth under different pH and salinity levels. For detection of enzyme activity the isolates were grown in culture media with the enzyme substrates as sole carbon source. The root colonization assay was performed on tomato seedlings grown on 0.6% water-agar medium. Growth under different pH and salinity levels was evaluated in AGS medium with 1%, 1.5%, 2%, 2.5%, and 3% NaCl, and pH levels adjusted to 5.0, 5.5, 6.0, 6.5, and 7.0. All isolates produced the enzymes amylase, catalase, and lipase, as well as indole acetic acid. With one exception (AC-92), all isolates presented cellulolytic and chitinolytic activity, and only AC-26 did not show xylanolytic activity. The isolates AC-147, AC-95, and AC-29 were the highest producers of siderophores. The isolates AC-26 and AC-29 did not show capacity for phosphate solubilization. All isolates colonized tomato roots in vitro, and AC-92 grew under all pH and salinity levels tested. The streptomycetes tested were considered as potential biocontrol and plant growth promotion agents.
Highlights
Palavras-chave: actinomicetos, ácido indolacético, enzimas extracelulares, sideróforos. The actinomycetes, mainly those belonging to the Streptomyces genus, make up an important group of soil bacteria from the actinobacteria class
Streptmycetes, plant growth and biocontrol studied because of their ample capacity for production of secondary metabolites, such as antibiotics and extracellular enzymes (Inbar et al, 2005). These microorganisms are abundant in soils and act in the degradation of complex molecules as well as recalcitrant substances, especially cellulose, lignocellulose, xylan and lignin, that play an important role in soil organic matter decomposition processes (Petrosyan et al, 2003; Ding et al, 2004)
Besides acting as organic matter decomposers, these microorganisms have great potential as agents for control of plant pathogens (Hoster et al, 2005; Thirup et al, 2001) and/or for plant growth promotion (Nassar et al, 2003). This is due to their capacity to produce antibiotics, siderophores, enzymes that have antimicrobial activity, substances that promote plant growth, solubilization of phosphates and competition with plant pathogens for substratum and nutrients (Cattelan & Hartel, 2000; Crawford et al, 1993)
Summary
The actinomycetes, mainly those belonging to the Streptomyces genus, make up an important group of soil bacteria from the actinobacteria class. This is due to their capacity to produce antibiotics, siderophores, enzymes that have antimicrobial activity, substances that promote plant growth, solubilization of phosphates and competition with plant pathogens for substratum and nutrients (Cattelan & Hartel, 2000; Crawford et al, 1993). Among the studies conducted in vitro aiming the selection of agents for biological control and plant growth, characteristics such as antagonistic activity against pathogens, capacity of colonizing the root system, production of siderophores, hydrolytic enzymes, and plant growth regulating substances are of fundamental importance (Cattelan, 1999).
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