The Culture Conditions And Mechanism Of Phosphorus-Solubilization Of The Phosphate-Solubilizing Bacteria, Bacillus Megaterium Var.Phosphaticum

A strain of phosphorus solubilizing bacteria, Bacillus megaterium var. phosphaticum,was studied by using egg yolk solid medium as a differential medium. The resolving capability to lecithin of the phosphorus solubilizing bacteria (PSB), optimal conditions for its incubation and lecithin-resolution were studied by means of incubation on a Petri Dish. The influence of culture conditions, e.g. temperature, pH and oxygen supply, and medium constituents, e.g. glucose, nitrogen and metals on the growth of PSB were also carefully studied to optimizing incubation conditions and composition of the liquid culture medium.In solid medium condition, the PSB grew well and its capability to resolve lecithin was optimized at 30癈 and pH range of 7.5-8.0. The bacteria propagated quickly and produced clearly discernible transparent circle around the colony.In liquid medium, PSB throve best when 20 ml medium was added into a 100 ml flask. Growth was significantly inhibited when medium volume was over 25 ml in a 100 ml flask. The PSB grew well in slightly alkaline conditions and the optimal pH for best growth was 8.5-9.0. The upper and lower limits to its growth were pH 10.5 and pH 4.4 respectively , in which the influence of pH on the growth of the PSB is not significant indicating the PSB is widely adaptive and self-adjustable to environmental pH. The optimal temperature for the best growth was 30癈. An orthogonal experiment of four factors and three levels was conducted to optimize incubation conditions of PSB in liquid culture medium. The results showed that the influence of nitrogen source was the most important factor to the growth of PSB, followed by the source of carbon. The pH was the least affecting during designed range. The optimum concentrations for N and C were 8X10'3g/ml and 2.1 Xl04g/ml, respectively. From the carbon source comparison, it was found that monosaccharide was the best C source to the PSB growth. Disaccharide was better than polysaccharides. Metals also have some effects on the initial growth of the PSB. Mg2*, Mn2*, and Ca2+ greatly improved the initial growth of the PSB while Fe2*and Al3*, especially Fe2* showed significant inhibitation. Cation of Na+, K*and Zn2+ had no significant effect The existence of lecithin showed its inhibition to the growth of PSB.Based on the simultaneous measurements of the PSB community, the bio-phosphorus(BP) and the available phosphorus (AP) in the liquid medium, the relationship among them were carefully analyzed. The lecithin-resolution of PSB has closely related with the bacteria's activity. The lecithin-resolution of PSB is active in lag phase and at the initial stage in exponential phase. The AP, BP, AP+BP and total phosphorus (TP) were measured to clarify the phosphorus transformation from lecithin. A phosphorus transformation rate of 12.5% of the PSB strain was detected. The phosphorus content of the PSB strain also varied at different phases, possibly due to its various requirements to phosphorus at different phases and different resolving ability to lecithin. At the final stage of lag phase of the growth curve, the AP in the liquid medium was higher than that in stationary and senescence phase. The stronger lecithin-resolving ability to lecithin may be explained partly for vigorous uptake to AP. The AP at the exponential phase was similar to that at the final stage of lag phase.Alkaline phosphatase activity (APA) was mainly detected in the exponential phase. It Increased along with the exponential phase and reached the maximum at transitional point between the lag and exponential phases, which might give a reasonable explanation to the AP changes in the liquid medium. By an analysis to the relationship between the APA and AP, APA could be considered as the most important influencing factor to the lecithin resolution by this strain.Influence of initial AP and lecithin in the liquid medium on the AP and bio-phosphorus resulted from the activities of PSB in the medium along with incubation was studied. Two self-adjusting mechanisms had been as...