Using lux genes marker technique to track Pseudomonas chlororaphis PL9L in cotton rhizosphere

Tn7-luxCDABE marker system was successfully transferred into Pseudomonas chlororaphis (strain PL9) by means of transformation and conjugation and a stable lux-marked strain PL9L was obtained. The colonizing dynamics and distribution of the luminescent bacteria PL9L in the rhizosphere of cotton planted in pots and rhizoboxes were studied by the methods of X-ray film imaging and enumeration of luminescent colonies on agar media, The results of pot culture experiment showed that PL9L successfully colonized in the rhizosphere of cotton. In pot cultures of sterile soil the highest colonizing level(3.1 x 10(2) cfu/g root soil) was reached on 6th day after seeds sown; On 56th day, the population of PL9L tended to stable and decreased to 1.7 x 10(9) cfu/g root soil) but in pot cultures of unsterile soil, the highest colonizing level(1.1 x 10(9) cfu/g root soil) was reached on 8th day. On 46th day, the population of PL9L tended to a stationary state, the numbers of them were 1.4 x 10(2) cfu/g root soil. The results of rhizobox culture experiment showed that PL9L spread from seeds toward the direction of root tip, but not synchronized with the stretch of roots. 6 days after seeds sown, in rhizobox culture of sterile soil, PL9L spread 12.0 cm below seeds, but in non-sterile soil was 11.0 cm. In the region of cotton root tip, PL9L were not detected.