| Applying phosphate-solubilizing bacteria strains (PSBs) into soil was one of the major methods to improve bioavailability of insoluble phosphates. In order to make effectively solubilize insoluble phosphates and improve phosphorus uptake of plants, PSBs should have the abilities to dissolve multifarious forms of insoluble phosphates. PSBs which could dissolve tricalcium phosphate, rock phosphate and lecithin were isolated and screened with modified Pikovskaya media in this paper. Culture conditions of growth and solubilizing insoluble phosphates, physiological characteristics and 16S rDNA gene sequence analysis of the isolated PSBs were carried out. Pot experiment was conducted to evaluate the isolated PSBs roles in dissolving phosphates and growth promotion to maize. The results obtained were as follows:(1) Sixteen strains, which could solubilize tricalcium phosphate, rock phosphate and lecithin were isolated from five calcareous soils collected from Jiangsu and Anhui province. Among all of the isolated strains, strain P1 was the most effective for solubilizing tricalcium phosphate, rock phosphate and lecithin. After 7 days incubation, strain P1 could produce water-soluble phosphorus (WPS) up to 674.5μg·mL-1,33.0μg·mL-1 and 33.0μg·mL-1, respectively, with tricalcium phosphate, rock phosphate and lecithin as insoluble phosphate source.(2) Strain P1 and P3 were identified as Burkholderia gladioli and Acinetobacter calcoaceticus, respectively, based on their physiological characteristics and 16S rDNA gene sequence analysis. Amplification of gabY and pqqE in P1 P2, P3, P4 and P5 strains by PCR method was carried, however, the DNA fragment of gabY genes was obtained only in strains P3, which showed 95% similarities with that in strain Pseudomonas cepaciaE37(U10242.1).(3) The optimal carbon and nitrogen sources for the growth of P1 and P3 were glucose, starch and glutamic acid peptone, respectively. While the optimal carbon and nitrogen sources for strain P1 and P3 dissolving phosphate were glucose, glucose and potassium nitrate and ammonium sulfate, respectively. During seven-day incubation by shaking at 170 rpm and 30℃in the liquid NBRIP media, the culture pH value of strain P1 and P3 fell to 5.03 and 4.98 on 1st day, respectively, and pH value of culture kept steady in the following days. WSP concentration in culture increased along with the incubation time. Simultaneously, WSP contents in tne medium decreased to a certain extent using dialysis tubing. The variation tendency of cell counts was that it declined at first, then raised, declined again, finally maintained at a stable level.(4) Five PSB bio-fertilizers significantly promoted the growth of maize as compared with organic fertilizer. Shoot height of maize seedling increased by 5.1%-33.8%, leaf length by 14.0%-38.0%, leaf width by 17.7%-37.6% and dry weight by 31.7%-177.1%, and phosphorus accumulation in maize increased by 41.6%～366.6%. The colonization numbers of P4 and P5 in maize rhizosphere soil were more than that of P1, P2 and P3 in pot experiment. Among the five treatments, P1 was the most effective one in promotion of maize growth, then P3, and P4 and P5 were the last. Besides, fermentation supernatants of P1 and P3 showed promotion to maize seed germination. P1 also had strong antagonistic activities against Phytophthoia capsici, Verticillium dahliae, Phytophthora parasitica var. nicotianae and Rhizoctonia solani.In summary, strains P1 and P3 with the abilities of solubilizing multifarious insoluble phosphates and antagonizing some soil-borne pathogens, showed promotion to maize growth both in pot and seed germination experiment, suggesting that their potential application in bio-organic fertilizer-producing is promising in future. |
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