Isolation and identification of phytate-degrading rhizobacteria with activity of improving growth of poplar and Masson pine.

A number of soil microorganisms can convert insoluble forms of phosphorus (P) to an accessible form to increase plant yields. Phytate is such a large kind of insoluble organic phosphorus that plants cannot absorb directly in soil, so the objectives of this study were to isolate, screen phytate-degrading rhizobacteria (PDRB), and to select potential microbial inocula that could increase the P uptake by plants. In this study, a total of 24 soil samples were collected from natural habitats of eight poplar and pine planting areas from the eastern to southern China. 17 PDRB strains were preliminarily screened from the rhizosphere soil of poplars and pines by the visible decolorization in the phytate selective medium. The highest ratio of the total diameter (colony + halo zone) to the colony diameter of the isolates was JZ-GX1, 3.85. Afterward, 17 PDRB strains were further determined for their abilities to degrade sodium phytate based on the amount of liberated inorganic P in liquid phytate specific medium. The results showed that the phytase ability of the three highest PDRB strains: JZ-GX1, JZ-DZ1 and JZ-ZJ1 were up to 2.58, 2.36 and 2.24 U/mL, respectively, much better than most of the bacteria reported in previous studies. In the soil-plant experiment, compared to CK, the best three strains of PDRB all could significantly promote growth of poplar and Masson pine under container growing. The three efficient PDRB strains were identified as follow: JZ-GX1, Rahnella aquatilis, both JZ-DZ1 and JZ-ZJ1 being autofluorescent, Pseudomonas fluorescens, by 16S rDNA gene sequencing technology, Biolog Identification System and biological characterization. The present study suggests that the three screened PDRB strains would have great potential application as biological fertilizers in the future.

Phytase-Producing Rahnella aquatilis JZ-GX1 Promotes Seed Germination and Growth in Corn (Zea mays L.).

Phytase plays an important role in crop seed germination and plant growth. In order to fully understand the plant growth-promoting mechanism by Rahnella aquatilis JZ-GX1, the effect of this strain on germination of maize seeds was determined in vitro, and the colonization of maize root by R. aquatilis JZ-GX1 was observed by scanning electron microscope. Different inoculum concentrations and Phytate-related soil properties were applied to investigate the effect of R. aquatilis JZ-GX1 on the growth of maize seedlings. The results showed that R. aquatilis JZ-GX1 could effectively secrete indole acetic acid and had significantly promoted seed germination and root length of maize. A large number of R. aquatilis JZ-GX1 cells colonized on the root surface, root hair and the root interior of maize. When the inoculation concentration was 107 cfu/mL and the insoluble organophosphorus compound phytate existed in the soil, the net photosynthetic rate, chlorophyll content, phytase activity secreted by roots, total phosphorus concentration and biomass accumulation of maize seedlings were the highest. In contrast, no significant effect of inoculation was found when the total P content was low or when inorganic P was sufficient in the soil. R. aquatilis JZ-GX1 promotes the growth of maize directly by secreting IAA and indirectly by secreting phytase. This work provides beneficial information for the development and application of R. aquatilis JZ-GX1 as a microbial fertilizer in the future.

The phosphate-solubilizing ability of Penicillium guanacastense and its effects on the growth of Pinus massoniana in phosphate-limiting conditions.

Microbes in soil can degrade insoluble inorganic and organic phosphorus, which are components of the soil phosphorus cycle and play an important role in plant growth. Pinus massoniana is a pioneer tree species used for afforestation in southern China and grows in poor, acidic soil. A shortage of available phosphorus in soil limits the growth of P massoniana To alleviate this situation, it is necessary to improve soil fertility. A fungal strain (JP-NJ2) with the ability to solubilize phosphate was isolated from the P massoniana rhizosphere. The ability of JP-NJ2 to solubilize inorganic and organic phosphorus and promote the growth of P massoniana was evaluated. It showed that JP-NJ2 could grow in NBRIP inorganic phosphate (AlPO4, FePO4·4H2O, and Ca3[PO4]2) fermentation broths, with the highest phosphorus concentration (1.93 mg/ml) and phosphate-solubilizing rate (43.7%) for AlPO4 and in Monkina organic phosphate fermentation broth with a phosphorus concentration of 0.153 mg/ml. The phosphate-solubilizing capability in inorganic and organic fermentation broths was negatively correlated with pH. JP-NJ2-produced acids at a total concentration of 4.7 g/l, which included gluconic (2.3 g/l), oxalic (1.1 g/l), lactic (0.7 g/l) and malonic (0.5 g/l) acids. It prioritized extracellular acidic phosphatase and combined with phytase to solubilize organic phosphates. The fungal suspension and extracellular metabolites from phosphate-solubilizing fungi promoted the shoot length of P massoniana seedlings by 97.7% and 59.5%, respectively, while increasing the root crown diameter by 46.8% and 27.7%. JP-NJ2 was identified as Penicillium guanacastense based on its morphology and phylogenetic analyses of five genes/regions (ITS, ben A, cmd, cox1 and tef). This is the first report on P guanacastense isolated from pine tree rhizosphere soil in China and its high phosphate-solubilizing capability, which promoted the growth of P massoniana P guanacastense JP-NJ2 has potential use as a biological fertilizer in forestry and farming.