| Rice rhizosphere bacteria Xanthomonas sp. P5310strain was resistant to highconcentration of chloramphenicol (Chl). Recipient strain P5310, donor strain E.coliWA803and assistant strain E.coliHB101have complementary resistances to antibiotics, so luxABgene was transferred into recipient strain P5310by the tri-parent conjugation method.Three kinds of bacteria were mixed culture by1.5:1.5:1.0ratio. Transformants ofP5310-luxAB were successfully obtained, and the transformation rate was18.95%. Thelabeled strain P5310-luxAB had a high luminescence activity and Chl, Km and Tcresistance. After being transferred in antibiotics plates for15times, P5310-luxAB still hadthe luminescence activity and resistant to three antibiotics. This indicated that the labeledstrain was stable in genetics. The plasmid transferred had no serious effect on the growthof the labeled strain, and hence the P5310-luxAB strain was suitable for soil andrhizosphere microecology researches.Purification process of rice germ lectin (RGL) was designed using the followingmethods: acetone degreasing, formic acid extraction，ammonium sulfate salt precipitationand chitin affinity chromatography. RGL was purified by353.59times, and the totalrecovery was160%. To detect affinity between RGL and the strain P5310, the RGLlabeled with FITC was applied to stain the strain P5310, and the result showed positivereaction.The labeled strain P5310-luxAB were co-incubated with the rice seedlings to studythe relationship between adsorption and the time, bacterial concentration, and riceseedlings disposed with RGL adsorbed more cells of strain P5310-luxAB. The resultsshowed that the adsorbed bacteria cells continued to increase with time and reached themaximum amount（5.93±0.03）×108CFU/g in60min. In the range of the concentration ofbacteria106-10~9CFU/mL, higher concentration of cells promoted the adsorption, and withthe bacteria concentration increasing the capacity increased. The isothermal adsorptiontests showed that the adsorption curve of P5310-luxAB cells accorded perfectly withLangmuir isothermal adsorption equation. The maximum saturated adsorption value wascalculated as3.33×10~9CFU/g with adsorption coefficient α=2.86×10-8. The young roots ofrice treated with RGL adsorbed as5.47times of P5310-luxAB cells as that of control, andshowed that RGL could promote the young rice roots to adsorb strain P5310-luxAB.The survival of the labeled strain in sterile and non-sterilized soils indicated that thelabeled strain had a similar survival dynamics regardless of the soil types. In the former25 days the number of bacteria showed a downward trend, but the number of bacteria innon-sterilized soil was lower than that in sterilized soil. This might reflect the fact that itwas not necessary for the labeled strain to compete with others for nutrients in sterile soil.On day25when carbon and nitrogen nutrients were supplied into soil, the number of strainin the soil began to rise. It indicated that as long as the nutrients in soil were available thestrain could well survive and colonizes. The survivals of the labeled strain in yellowcinnamon soil and in sandy loam have similar results. The above results showed that thelabeled strain had good survival and colonization ability in different soils and can beapplied in rhizosphere ecology studies.Different types of microorganisms have the different abilities to produce siderophores.Microbial siderophore transport system is an important way to get iron. The original strainP5310and the labeled strain P5310-luxAB produced the same amount of siderophore,which could be marked with five "+" with the A/Ar ratio being equal. It was proved thatluminescence gene transferred into the original strain did not influence the production ofsiderophore of strain P5310-luxAB. Therefore, it is a practicable way to replace the P5310with P5310-luxAB for ecological studies.Rice cultivation experiments showed that strain P5310-luxAB promoted growth ofrice seedlings, increasing the fresh and dry weight as well on rice plant height. |
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