A novel method for the isolation of motile bacteria using gradient culturesystems

Isolation of motile bacteria from stream water samples was achieved by usin g Lutrol F127 (poloxamer 407) as a gelling agent in culture media. This blo ck copolymer has the property of repeatedly liquefying and solidifying at l ow and high temperatures, respectively. The ability of motile bacteria to m ove through liquid-state Lutrol F127 towards a higher nutrient concentratio n was exploited. After establishment of the nutrient gradient and inoculati on, the system was cooled to liquefy the medium and kept liquid to allow mo tile bacteria to move. Raising the temperature allowed solidification and p revented further movement. Colonies could be easily removed. The proportion of motile isolates (determined by microscopic observation) increased from 42% in the indigenous population to 100% after isolation using the gradient system. (C) 2001 Elsevier Science B.V. All rights reserved.