Production of biosurfactants and antibiotics by fluorescent pseudomonads isolated from a closed hydroponic system equipped with a slow filter

The presence of antibiotic- and biosurfactant-producing strains of fluorescent pseudomonads in a closed hydroponic system equipped with a slow filter was investigated. A total of 271 strains of pseudomonads were isolated before the filter, from the filter skin and from the effluent. Production of biosurfactants was determined using the drop-collapse method. The ability of the strains to inhibit the growth of the plant pathogens Pythium ultimum, Phytophthora cryptogea and Fusarium oxysporum was determined using dual culture plating. The influence of carbon sources on production was determined for selected strains, which also were identified to species level. Production of antibiotics or biosurfactants was observed to be a common trait among the fluorescent pseudomonads within the closed hydroponic system and it was affected by the filter. Pythium ultimum was the pathogen that was most sensitive to antibiotics produced by the fluorescent pseudomonads. The results indicated a strong influence of nutritional resources on antibiotic and biosurfactant production.