| luxAB gene was transferred into Pseudomonas sp. JK45 strain by the tri-parent conjugation method to study the autecology of an important plant growth promotion rhizobacteria. The JK45 cells prepared from initial logarithmic growth phase were more likely to be sensitive to foreign DNA and the maximum transfer frequency was up to 8.71×10-5. In addition, the optimal mating ratio was 1:1:1 for the three parents. The labeled strain JK45-L had a high luminescence activity and Chl, Km and Tc resistance. After being inoculated in plates with antibiotics for 15 times, JK45-L still had the luminescence activity and resistant to three antibiotics. All of these facts meant that JK45-L was stable in genetics. The plasmid transformed had no serious effect on the growth and physiological and biochemical character of JK45-L strain, and the potassium-releasing ability of the strain didn't change, and hence, the JK45 was suitable for soil and rhizosphere microecology researches.The labeled strain JK45-L was stable, and can be used as microbial inoculant. After it was inoculated into the soil, the colonizing dynamics of the JK45-L in soil were studied by the method of enumeration of luminescent colonies on agar media. The results showed that JK45-L successfully colonized both in the sterile soil and unsterile soil, and colonizing level of JK45-L in sterile soil was higher than that of unsterile soil. The population of JK45-L rised when C and N nutrients were added into soil. The population of JK45-L reached to the highest level, 6.5×107cfu/g and 3.6×107cfu/g soil respectively in the sterile soil and unsterile soil after 5 days, with initial inoculation dose of 2.7×108cfu/g soil. With time delaying the population decreased. The results of survival ability of JK45-L in yellow cinnamon soil and yellow fluovo-aquic soil meant that strain JK45-L could compete with other microbes for space and nutrition in different soils.Being prepared as microbial inoculant and inoculated on seeds of wheat, the colonizing dynamics and distribution of the strain JK45-L in rhizosphere of wheat plant in rhizoboxes were studied by the method of enumeration of luminescent colonies on agar media. The results showed that colonizing level of labeled strain in sterile soil was higher than that of unsterile soil, and the strain colonized mainly in 0-10cm root segment in vertical direction. The population of JK45-L reached to the highest level before 10 days after seeds planted. On the 5th day JK45-L spread 6cm below seeds, the population in 0-2cm and 2-4cm root segment was 1.94×106cfu/g rhizosphere soil, 1.22×106cfu/g rhizosphere soil in unsterile soil respectively, and 4.13×106cfu/g rhizosphere soil, 1.25×106cfu/g rhizosphere soil respectively in sterile soil. No luminescent bacteria were detected below 6cm, although wheat root length was beyond 6cm. On the 10th day, labeled strain colonized mainly in 0-10cm root segment, although wheat root length was beyond 12cm, and on the 60th day, the population of JK45-L in 0-2cm root segment reached to 1.13×103cfu/g root-soil and 1.07×104cfu/g root respectively in wheat rhizosphere and wheat rhizoplane. The results of rhizobox culture experiment showed that JK45-L spread from seeds toward the direction of root tip, but not synchronized with the stretch of roots. JK45-L was not detected in the region of wheat root tip.Colonizing level of JK45-L in wheat rhizoplane was higher than that of wheat rhizosphere, and the population of JK45-L decreased gradually along the root. The data indicated that the colonizing level of strain JK45-L was relative to the distance between the root segment and the seeds, the shorter the distance was, the higher the coloning level was. In addition, the population of JK45-L in the same root segment decreased gradually with time delaying.Strain JK45 was isolateded from wheat rhizosphere and has strong potassium-releasing abiliity. After being inoculated on wheat root, the labeled strain JK45-L could successfully colonize in wheat root with a higher level. Hence the strain can be prepared as microbial inoculant and inoculated on wheat root for pot experiments and field experiments to offer data for the development of microbe fertilizer.
|
PDF Full Text Request