Phosphate-dissolving Characteristics Of Inorganic Phosphate-solubilizing Bacteria And Their Effect On Phosphorus Release From The Sediments In Rongcheng Swan Lake

Green tides have occurred frequently in the Yellow Sea in recent decades.The outbreak and decline of macroalgae blooms have caused a serious impact on the water environment.Phosphorus（P）is an important inducement of eutrophication and algal blooms in most waters.Inorganic phosphate-solubilizing bacteria（IPB）is an important factor affecting P release from the sediments and play a key role in P biogeochemical cycle in waters.Chaetomorpha linum have outbreak frequently in recent years in Rongcheng Swan Lake.Through the laboratory screening and simulation,the phosphate-solubilizing ability of indigenous microorganisms in sediments was studied in algae outbreak area and non-outbreak area,and the IPB strains were screened and identified from the surface sediments in Swan Lake.In addition,the phosphate-solubilizing ability of different IPB strains was analyzed under separate and mixed inoculation conditions.The effects and mechanism of IPB strains on P release from the sediments were discussed.The main results are as follows:（1）In Swan Lake,the indigenous microorganisms in sediments were able to dissolve tricalcium phosphate,whose phosphate-solubilizing ability were stronger at the western,northern and central lake.At the treatments of autumn and spring sediments,the p H in liquid medium decreased to 4.78～4.87 and 4.35～5.31,while the maximum concentrations of soluble reactive phosphorus（SRP）ranged at 217.44～256.09 mg L^-1and 201.01～333.02mg L^-1,respectively.At different lake areas,the highest SRP in autumn and spring sediments were observed in the north and central lake area,respectively,while the lowest p H both appeared at the western lake.（2）During the plate screening process,the IPB isolates showed great differences in their morphological characteristics and the size of phosphate-solubilizing halos.In this research,ten IPB strains were isolated from the sediments of Swan Lake,and their taxonomy was determined by 16S r DNA sequence analysis.The ten IPB strains isolated belonged to one family（Bacillaceae）,two genera（Bacillus sp.and Geobacillus sp.）and four species（Bacillus flexus,Bacillus megaterium,Bacillus licheniformis and Geobacillus stearothermophilu）.Bacillus was the main genus of IPB in the sediments from Swan Lake.（3）The phosphate-solubilizing characteristics of obtained IPB strains（IPB1-IPB10）were evaluated using liquid medium.In the liquid medium culture,all IPB strains were able to dissolve tricalcium phosphate,but the phosphate-solubilizing ability varied greatly among different IPB strains.During the culture period,the p H of medium reduced to4.10～5.06.The concentrations of SRP in medium was obviously increased,and the maximum concentrations of SRP in every medium ranged at 99.75～209.55 mg L^-1.Bacillus megaterium strain showed the strongest phosphate-solubilizing ability,resulting in the highest SRP concentration in the liquid medium cultures.In this research,the secretion of acids was the main mechanism of phosphate solubilization by IPB of Rongcheng Swan Lake,and there was a significant negative correlation between SRP concentration and p H value（P<0.01）.The phosphate-solubilizing ability of the IPB was promoted when strains were grown in mixed-strain cultures.（4）Through inoculating Bacillus megaterium,Bacillus licheniformis,Bacillus flexus into the sediments,the ability of IPB strains to dissolve phosphate from sediments of different lake area was investigated by shaking flask culture.And the results showed that the calcium-bound phosphorus（HCl-P）concentration in the sediments decreased greatly under different IPB conditions.Compared with the initial value,HCl-P concentration decreased by 17.84～25.90 mg kg^-1in sediments from the central lake.At the water of three bacterial inoculated sediments from the north and central Lake areas,the p H decreased to4.17～4.55 and 4.56～4.61,and the maximum concentrations of SRP ranged at 0.18～0.37mg L^-1and 0.09～0.18 mg L^-1,respectively.Bacillus megaterium showed a strong phosphate-solubilizing ability in sediments of two lake areas.（5）The indoor simulation test was carried out with three IPB strains and the sediments of central lake area.During the early stage of the experiment,water p H value decreased at the treatments inoculated with IPB,and the p H of sterilized-sediment group and non-sterilized sediment group decreased to 6.46～6.76 and 6.66～6.78,respectively.Water Eh at different treatments decreased continuously with time during the experiment,and the interface of sediment and water was anaerobic at the end.For the sterilization group,the inoculation of IPB promoted the release of phosphorus from sediments significantly.During the later stage,water total phosphorus（TP）concentration at the inoculation treatments was much higher than that of the control,with the difference being0.06～0.30 mg L^-1.In the non-sterilization group,TP concentrations increased slowly with time,and there was small difference among different IPB treatments.At the end of the experiment,the concentrations of HCl-P in most sediments inoculated with IPB decreased obviously,with a decline of 19.92～50.08 mg kg^-1,and BD-P concentrations decreased by1.81～4.19 mg kg^-1.However,Na OH-P concentration did not decrease.The results indicate that the inoculation of IPB can reduce water p H greatly,which led to the dissolution and release of HCl-P from the sediments.In Rongcheng Swan Lake,HCl-P is the main form of sediment phosphorus,under the action of IPB,whose effect on the P level in overlying water can not be ignored.