Transformation of inorganic P fractions of soil and plant growth promotion by phosphate-solubilizing ability of Penicillium oxalicum I1.

The solubilization of tricalcium phosphate is often considered as the standard for screening of most phosphate-solubilizing microorganisms (PSMs). However, usually the effect of large-scale application of PSM on the promotion of crop growth varies. This study presents an efficient method for screening and testing phosphate-solubilizing fungus that enhance plant growth. A fungus Penicillium oxalicum I1 (P-I1) was isolated and identified that had high ability of phosphate-solubilization and could utilize maize root exudates as sources, and propagate well in vitro and in soil. P-I1 excreted oxalic acid and reached 593.9 µg/ml, and the pH value was decreased from 6.90 to 1.65 in 26 h. The amount of P-I1 increased by 48-fold in 28 d and was maintained for 49 d in soil. PSM showed selectivity on the transformation of the different forms of phosphorus, a wide range of insoluble phosphates, such as Ca8H2(PO4)6·5H2O, AlPO4, FePO4, and Ca10(PO4)6(OH)2, were converted to soluble CaHPO4in soil, and CaHPO4was also inhibited from being converted into insoluble phosphate by P-I1. The Ca2-P content reached 27.11 µg/g soil on day 28 at 20°C, which increased by 110.32%, and plant growth promotion was tested and verified, the results showed that maize yield increased remarkably than control after inoculated P-I1, maize yield increased maximum by 14.47%. The data presented that P-I1 appear attractive for exploring their plant growth-promoting activity and potential field application.

[Screening of two phenanthrene-utilizing and high-effective phosphorus-accumulating bacteria and their effects on phosphorus-accumulating characteristics].

In this study, two phenanthrene-utilizing and high-effective P-accumulating bacteria Y11 and Y4-2 were isolated from sludge samples of Taihu Lake using plate culture and blue-colored colonies methods. Strains Y11 and Y4-2 were identified as Acinetobacter sp. according to the results of morphology, physiology and the phylogenetical analyses of 16S rDNA sequences. The two strains showed high effective P-accumulating ability in plate and broth cultures. Y11 could grow well from 10 degrees C to 35 degrees C and pH from 6 to 9, Y4-2 could grow well from 10 degrees C to 35 degrees C and pH from 6 to 8. Phenanthrene could be used as sole carbon and energy sources. In our experiment, high phosphorus concentration in broth culture had no negative effect on the growth of strain Y11, however the growth of strain Y4-2 was slightly affected. Under cultivation condition of 30 degrees C, 170 r/min, 1% inoculation (D600 = 0.4), the accumulation of phosphorus was various by strains and cultivation concentration of phosphorus as well: In 2 mg/L phosphorus concentration medium, the highest phosphorus-accumulation ratio of strains Y11 and Y4-2 were 96.13% and 94.65%, the phosphorus concentration decreased from 2 mg/L to 0.08 mg/L and 0.11 mg/L, respectively. In 5 mg/L phosphorus concentration medium, the highest phosphorus-accumulation ratio of strains Y11 and Y4-2 were 95.94% and 71.19%, the phosphorus concentration decreased from 5 mg/L to 0.20 mg/L and 1.44 mg/L, respectively. In 8 mg/L phosphorus concentration medium, the highest phosphorus-accumulation ratio of strains Y11 and Y4-2 were 71.24% and 47.81%, the phosphorus concentration decreased from 8 mg/L to 2.30 mg/L and 4.18 mg/L, respectively. For the P removal of Yunnan Dianchi water sample containing 1.01 mg/L phosphorus, Y11 and Y4-2 were successful to decrease the phosphorus concentration from 1.01 mg/L to 0.06 mg/L in 6 h and 48 h, respectively. The results indicated that Acinetobacter sp.Y11 and Y4-2 possess high ability of phosphorus removal and suitability to various water environments. Y11 strain adapt to all kinds of eutrophic waterbody even polluted with phenanthrene, Y4-2 adapt to pH < or = 8.0 eutrophic waterbody with phenanthrene pollution.