Abstract
In the present study, isolation and identification of microorganisms from rhizospher of garden soil with biosurfactant producing ability and characterization of biosurfactants were studied. The results exhibited capability of four isolates for biosurfactant production among six isolates. The isolate Pseudomonas aeruginosa NH22 showed a better emulsifier producer, therefore it selected for biosurfactant production and antifungal activity in the present study. Biochemical analysis of partially purified bioemulsifier demonstrated that the biosurfactant contains mono, and di- rhamnolipid with Rf values of 0.82 and 0.32 respectively. Rhamnolipid efficiency tested for antifungal activity by determination percentage reduction of radial growth, fresh and dry weight and laccase activity of fungus. Maximum reduction in radial growth 76%, and reduction of biomass obtained at rhamnolipid concentration of 1000 µg/ ml. Maximum laccase activity obtained 0.921 U/ml also at rhamnolipid concentration of 1000 µg/ ml, while reduction about 21% of the enzyme activity recorded at higher rhamnolipih concentration of 1500 µg/ ml. The critical micelle concentration estimated to be 200 mg/l, which led to reduce surface tension value of the culture to34 mN/m.
Highlights
Biosurfactants are extracellular macromolecules produced by bacteria, yeast and fungi and in particular by natural and recombinant bacteria when grown on different carbon sources
The results showed that the mycelial growth inhibited at a cyclic lipopeptide (CLP) concentration of 10 μg/ml and higher, fresh and dry weight of Pythium infestans decreased logarithmically with increasing concentrations of CLP reaching the maximum reduction in biomass at CLP concentration of 50 μg/ml and higher
The antifungal activity increased with increasing concentration of biosurfactant and maximum zone of inhibition obtained (48.8) mm with Botrytis cinerea at a biosurfactant concentration of 3.2 g/l. [17] found effective antifungal activity of rhamnolipid and sophorolipid against plant and seed pathogenic fungi
Summary
Biosurfactants are extracellular macromolecules produced by bacteria, yeast and fungi and in particular by natural and recombinant bacteria when grown on different carbon sources. Different Pseudomonas strains have the ability to inhibit the growth and activity of a wide range of plant pathogens, including fungi, nematodes and bacteria [2]. Some Pseudomonas strains have been recognized as antagonists of plant fungal pathogens and antibiotic producers. This is probably due to the abundance of this diverse group of bacteria and their obvious importance in the soils [4]. Rhamnolipids produced by strains of Pseudomonas aeruginosa were shown to be highly effective against plant pathogens, including Pythium aphanidermatum, Plasmopara lactucae-radicis, Rhizoctonia solani and Phytophthora capsici. Rhamnolipid B, produced by P. aeruginosa B5, has lytic effects on zoospores and inhibitory activity against the spore germination and hyphal growth of several other pathogens. The isolate Rhizoctonia solani was grown on Potato dextrose agar (PDA) and incubated at 25oC for 72h
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