Research On Screening Of Phosphate-solubilizing Bacteria And Their Ecological Characteristics

Phosphorus is a necessary basic element for the growth of phytoplankton in aquacultureponds. In the pond system, the phosphorus concentrations are high in the sediment but low in theoverlying water. And the utilization of phosphorus in the shrimp ponds is low. Phosphate-solubilizing bacteria (PSB) are considered to play important ecophysiological roles whichmobilize insoluble phosphorus in sediment for phytoplankton. However, the amounts of PSB areat a very low level. Whether it can improve the utilization rate of phosphorus by adding PSB ornot become the focus of research. In this study, high efficiency PSB strains were isolated. Andthe adaptabilities of different temperature, salinity and initial pH on isolated strains were studied.The phosphorus release effects of PSB on feed and simulated ponds were studied to provide thetechnical support for the application of PSB in aquaculture ponds. The main research content isas follows.PSB strains were isolated from the sediment of ponds, the laboratory strains and purchasedstrains by preliminary screening of plate assay and quantitative assessment of broth assay. Thenthe strains were identified by16S rDNA sequence analysis and Biolog identification. The resultsshowed that four strains of PSB were isolated from the sediment of pond, which were HY-3,HY-4, HY-5and HY-6. After5d cultivation, their activities resulted in accumulations of solublephosphate56.85mg/L,64.67mg/L,27.88mg/L and48.34mg/L, respectively. By16S rDNAsequence analysis and Biolog biochemical identification, the strain of HY-3and HY-6wereidentified as Bacillus amyloliquefaciens, HY-4was identified as Paenibacillus pabuli, and HY-5was identified as Baciilus licheniformis.Given to the environmental conditions of aquaculture ponds, the adaptabilities of differenttemperature, salinity and initial pH on strains HY-3and HY-6were studied. The results showedthat strain HY-3could tolerate a wide range of temperature and salinity, which could grow wellin15～35℃, pH6～8and salinity10～40. And under the condition of25～35℃, pH6～8,salinity10～40, strain HY-3had good phosphate-solubilizing effect. Moreover, the maximumphosphate-solubilization was observed at120h, which was64.53mg/L. Strain HY-6also couldtolerate a wide adaptation range of temperature and salinity, which could grow well in15～35℃,pH6～8,0～40. And under the condition of25～35℃, pH6～7,0～40(salinity), strain HY-6had good phosphate-solubilizing effect. The maximum phosphate-solubilization of HY-6wasalso observed at120h, which was75.33mg/L. The results indicated that strain HY-3would beapplied in the seawater aquaculture ponds, while strain HY-6would adapt to the freshwater andseawater aquaculture ponds environment. Then the growth characteristics of strain HY-3and HY-6and the highest amount ofphosphate dissolving were studied. Results showed that in the organic phosphorus liquid medium,the amount of these two strains could reach up to109cfu/mL. Strains of HY-3had the highestphosphate-solubilizing in9d, which was118.92mg/L under the condition of salinity10, andwhich was105.14mg/L under the condition of salinity40. Furthermore, the decreasing ofphosphate in the medium under salinity10was slower than40. Strain HY-6had the highestphosphate-solubilizing in9d, which was116.52mg/L under the condition of salinity10, andwhich was126.29mg/L under the condition of salinity20.According to the variation range of pH in the aquaculture ponds and the difference ofphosphate-solubilizing effect between initial pH8and9, the growth and phosphate-solubilizingvariation of strain HY-3and HY-6under the initial pH from8to9were further studied. Theresults showed that both strain HY-3and HY-6could grow well when the initial pH is not higherthan8.5, which the amount of bacteria could reach up to108cfu/mL. The amounts ofphosphate-solubilizing were reach up to70.96～115.49mg/L and84.53～84.53mg/L,respectively. When the initial pH was higher than8.5, the growth of two strains and thephosphate-solubilizing effect was not ideal.Using prawns feed as medium, the release phosphorus effects of strain HY-3, HY-4, HY-5and HY-6on organic matter were discussed, The results showed that the growth of these strainsin the shrimp feed solution was well, which the amount of bacteria can grow from103cfu/mL to108cfu/mL. Compared with the control group, the phosphate solubilization efficiency of strainHY-4, HY-3, HY-5and HY-6could improve56.16%,41.99%,16.09%and7.20%, respectively.Finally, the effects of phosphorus release of strain HY-3and HY-6in simulated pondenvironment were investigated. The results showed that strain HY-3and HY-6both couldincrease the phosphate content in water, meanwhile reduce the content of total phosphorus (TP)in the sediment. Compared with the control group, the contents of phosphate in water wereincreased by14times and8times, and TP were decreased by (9.17±1.40)%and (9.17±4.76)%, respectively.