Abstract
The dichloromethane extract of culture filtrate from Streptomyces aburaviensis R9 was evaluated using various rapid bioassays to determine potential inhibitory effects towards phytopathogenic fungi (Colletotrichum acutatum, C. fragariae, C. gloeosoprioids, Botrytis cinerea, Fusarium oxysporum, Phomopsis viticola and P. obscurans), fish bacterial pathogens (Edwardsiella ictaluri and Flavobacterium columnare), a green alga (Selenastrum capricornutum), plant seeds [Bent grass (Agrostis sp.) monocot and lettuce (Lactuca sativa) dicot] and 2-methylisoborneol (MIB)-producing cyanobacteria (Planktothrix perornata and Pseudanabaena sp.). The dichloromethane extract showed selective inhibition against the cyanobacterium P. perornata, with a lowest-complete-inhibition concentration (LCIC) of 10 mg/L and lowest-observed-effect concentration (LOEC) of 10 mg/L while LCIC and LOEC values were 100 mg/L when tested against S. capricornutum. This extract also showed slight meristematic cytogenic necrosis at 200 mg/L towards germinated seeds of both test plants. The compounds were not very toxic towards the channel catfish (Ictalurus punctatus) pathogenic bacteria E. ictaluri and F. columnare. Preliminary evaluation of the extract toward C. acutatum, C. fragariae and C. gloeosoprioids using TLC bioautography revealed moderate activity. However, further evaluation of the extract using a microtiter plate bioassay determined that inhibition was strongest against C. acutatum and C. fragariae, though this inhibitory activity diminished at 72 hours and was moderately less active than the commercial fungicides azoxystrobin and captan when comparing 1 - 100 mg/L levels at 48 hours.
Highlights
Biological methods and technologies in coordination with agricultural production [1,2] were established to solve problems of the deleterious effects of chemical fertilizers and pesticides on the environment and the appearance of organisms with resistance resulting from the high application rates of currently used agrochemicals [3,4,5]
The majority of those isolates producing bioactive compounds belong to species within the genus Streptomyces, and several Streptomyces spp. have been advocated as promising biocontrol agents against several phytopathogenic fungi and bacteria [9,10,11,12,13,14]
In addition to potential herbicidal activity, the extract was evaluated using rapid bioassays for activity against off-flavor compound-producing species of cyanobacteria, bacterial pathogens of catfish, and fungal phytopathogens in order to determine if other useful bioactive compounds were produced by S. aburaviensis R9
Summary
Biological methods and technologies in coordination with agricultural production [1,2] were established to solve problems of the deleterious effects of chemical fertilizers and pesticides on the environment and the appearance of organisms with resistance resulting from the high application rates of currently used agrochemicals [3,4,5]. Microorganisms are ubiquitous in nature and wellknown to produce bioactive materials of particular practical value Among these beneficial microorganisms are the actinomycetes, a group of filamentous bacteria which include many species that are characterized by the production of important extracellular bioactive compounds including antibiotics [7,8]. Members of the genus Streptomyces are well known for their potential to produce herbicides [5,15] Natural compounds, such as the secondary metabolites of actinomycetes and streptomycetes, have been demonstrated to be bioherbicides and include anisomycin, bialaphos, herbicidans A and B [5]. In addition to potential herbicidal activity, the extract was evaluated using rapid bioassays for activity against off-flavor compound-producing species of cyanobacteria (blue-green algae), bacterial pathogens of catfish, and fungal phytopathogens in order to determine if other useful bioactive compounds (toxins) were produced by S. aburaviensis R9
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