Phosphorus Solubilization Ability Research Articles

Building microbial consortia to enhance straw degradation, phosphorus solubilization, and soil fertility for rice growth

Straw pollution and the increasing scarcity of phosphorus resources in many regions of China have had severe impacts on the growing conditions for crop plants. Using microbial methods to enhance straw decomposition rate and phosphorus utilization offers effective solutions to address these problems. In this study, a microbial consortium 6 + 1 (consisting of a straw-degrading bacterium and a phosphate-solubilizing bacterium) was formulated based on their performance in straw degradation and phosphorus solubilization. The degradation rate of straw by 6 + 1 microbial consortium reached 48.3% within 7 days (The degradation ability was 7% higher than that of single bacteria), and the phosphorus dissolution rate of insoluble phosphorus reached 117.54 mg·L− 1 (The phosphorus solubilization ability was 29.81% higher than that of single bacteria). In addition, the activity of lignocellulosic degrading enzyme system was significantly increased, the activities of endoglucanase, β-glucosidase and xylanase in the microbial consortium were significantly higher than those in the single strain (23.16%, 28.02% and 28.86%, respectively). Then the microbial consortium was processed into microbial agents and tested in rice pots. The results showed that the microbial agent significantly increased the content of organic matter, available phosphorus and available nitrogen in the soil. Ongoing research focuses on the determination of the effects and mechanisms of a functional hybrid system of straw degradation and phosphorus removal. The characteristics of the two strains are as follows: Straw-degrading bacteria can efficiently degrade straw to produce glucose-based carbon sources when only straw is used as a carbon source. Phosphate-solubilizing bacteria can efficiently use glucose as a carbon source, produce organic acids to dissolve insoluble phosphorus and consume glucose at an extremely fast rate. The analysis suggests that the microbial consortium 6 + 1 outperformed individual strains in terms of both performance and application effects. The two strains within the microbial consortium promote each other during their growth processes, resulting in a significantly higher rate of carbon source consumption compared to the individual strains in isolation. This increased demand for carbon sources within the growth system facilitates the degradation of straw by the strains. At the same time, the substantial carbon consumption during the metabolic process generated a large number of organic acids, leading to the solubilization of insoluble phosphorus. It also provides a basis for the construction of this type of microbial consortium.

Studies on the Phosphorus-Solubilizing Ability of Isaria cateinannulata and Its Influence on the Growth of Fagopyrum tataricum Plants.

I. cateinannulata has been shown to promote the growth of F. tataricum. However, whether its growth-promoting capacity is related to its ability to solubilize phosphorus has not been reported. Therefore, in this study, we sought to assess the phosphorus-solubilizing ability of 18 strains of I. cateinannulata by analyzing their growth in an inorganic phosphorus culture medium. The effects of F. tataricum on growth and effective phosphorus content were analyzed through field experiments. The results showed that all 18 strains of I. cateinannulata had a phosphorus release capacity, with phosphorus solubilization ranging from 5.14 ± 0.37 mg/L to 6.21 ± 0.01 mg/L, and strain 9 exhibited the best phosphorus solubilization effect. Additionally, the field results demonstrated that I. cateinannulata positively influenced the growth, root length, and yield of F. tataricum by increasing the chlorophyll and soluble phosphorus content. This study will provide a material basis and theoretical support for investigating the interaction mechanism between I. cateinannulata and F. tataricum.

Transcriptomic analysis and carbohydrate metabolism-related enzyme expression across different pH values in Rhizopus delemar.

pH is one of the important factors affecting the growth and performance of microorganisms. We studied the pH response and plant growth-promoting (PGP) ability of Rhizopus delemar using cultivation experiments and transcriptomics, and verified the expression profiles using quantitative real-time PCR. pH affected the growth and PGP properties of R. delemar. At pH 7, the growth rate of R. delemar was rapid, whereas pH 4 and 8 inhibited mycelial growth and PGP ability, respectively. In the pot experiment, the plant height was the highest at pH 7, 56 cm, and the lowest at pH 4 and pH 5, 46.6 cm and 47 cm, respectively. Enzyme activities were highest at pH 6 to pH 7. Enzyme activities were highest at pH 6 to pH 7. Among the 1,629 differentially expressed genes (DEGs), 1,033 genes were up-regulated and 596 were down-regulated. A total of 1,623 DEGs were annotated to carbohydrate-active enzyme coding genes. The PGP characteristics, e.g., Phosphorus solubilization ability, of R. delemar were strongest at pH 7. The results provide useful information regarding the molecular mechanism of R. delemar pH response.

Effects of Priestia aryabhattai on Phosphorus Fraction and Implications for Ecoremediating Cd-Contaminated Farmland with Plant-Microbe Technology.

The application of phosphate-solubilizing bacteria has been widely studied in remediating Cd-contaminated soil, but only a few studies have reported on the interaction of P and Cd as well as the microbiological mechanisms with phosphate-solubilizing bacteria in the soil because the activity of phosphate-solubilizing bacteria is easily inhibited by the toxicity of Cd. This paper investigates the phosphorus solubilization ability of Priestia aryabhattai domesticated under the stress of Cd, which was conducted in a soil experiment with the addition of Cd at different concentrations. The results show that the content of Ca2-P increased by 5.12-19.84%, and the content of labile organic phosphorus (LOP) increased by 3.03-8.42% after the addition of Priestia aryabhattai to the unsterilized soil. The content of available Cd decreased by 3.82% in the soil with heavy Cd contamination. Priestia aryabhattai has a certain resistance to Cd, and its relative abundance increased with the increased Cd concentration. The contents of Ca2-P and LOP in the soil had a strong positive correlation with the content of Olsen-P (p < 0.01), while the content of available Cd was negatively correlated with the contents of Olsen-P, Ca2-P, and LOP (p < 0.05). Priestia aryabhattai inhibits the transport of Cd, facilitates the conversion of low-activity P and insoluble P to Ca2-P and LOP in the soil, and increases the bioavailability and seasonal utilization of P in the soil, showing great potential in ecoremediating Cd-contaminated farmland soil with plant-microbe-combined technology.

Inoculation of cold-adapted microbial consortium screened from alpine meadows promotes the growth of mixed grasses by changing soil properties and enzyme activity

The objective of this study was to investigate the effect of co-inoculation of three PGPR strains and inoculation ratio on the growth characteristics and soil properties of mixed grasses. In this study, we used 3 strains of PGPR for the material, which were Acinetobacter calcoaceticus called HMAJ1, Pseudomonas piscium called HMAJ5, and Pseudarthrobacter psychrotolerans called NCZ1, with nitrogen fixation and phosphorus solubilization ability. By mixing the bacteria in a different ratio, the effect of inoculating with a microbial consortium on the plant and soil properties of mixed grasses (Elymus nutans Griseb, Festuca sinensis, and Poa pratensis L.) was evaluated and the best microbial inoculants ratio was selected. The results showed that inoculating with a microbial consortium increased the soil organic carbon , available phosphorus, ammonium and nitrate nitrogen content, and the activities of soil alkaline phosphatase, sucrase, peroxidase, and urease, which promoted the plant height and biomass of mixed grasses. Pearson correlation analysis showed that plant characteristics were differently correlated with soil properties. Grey correlation analysis of plant biomass, soil properties, and soil enzyme activity revealed that T7 (HMAJ1:NCZ1 = 3:7) was the most effective in improving mixed-grasses biomass and soil quality. Our results indicated that the positive interaction of nitrogen-fixing bacteria with phosphorus-solubilizing strains may become a novel and effective bio-inoculant to achieve sustainable pulse productivity.

Screening and identification of a Burkholderia strain and optimization of its phosphate solubilizing capacity

In order to solve the problem that soil soluble phosphorus content in most cultivated land in China is insufficient and the plant growth is inhibited, a phosphate solubilizing microorganism (PB) was screened and identified, and its phosphate solubilizing performance was optimized. The results showed that the PB strain was belonged to Burkholderia stabilis. It had the ability of nitrogen fixation and indole-3-acetic acid (IAA) secretion, as well as a certain inhibitory effect on Escherichia coli. It could maintain high activity and phosphorus solubilizing ability at pH 8.0-10.0, indicating good alkali resistance. The results of phosphorus dissolving performance optimization showed that the phosphate solubilizing capacity of strain PB reached the best at 30℃, pH 7.0, 180 r·min-1, using glucose as carbon source, ammonium sulfate as nitrogen source, tricalcium phosphate as phosphorus source and adding 50 μmol·L-1 lysine. The amount of dissolved phosphorus was 569.33 mg·L-1, which was 1.9 times of that before optimization. The strain mainly secreted citric acid, malonic acid, and glucuronic acid during metabolism. After adding lysine, the type of organic acids secreted by the strain did not change, but the content increased significantly. Results from pot experiments showed that the application of PB bacterial fertilizer could significantly improve the growth and physiological indicators of garlic seedlings, and that the promotion effect was more obvious after adding lysine. Compared with the control, the height of seedling was increased by 18.6%, seedling diameter was increased by 16.7%, aboveground fresh and dry weight were increased by 22.1% and 15.7%, and belowground fresh and dry weight were increased by 22.0% and 28.7%, respectively in PB with lysine treatment. Soil available phosphorus content was 2.1 and 2.3 times of the control in PB and PB+lysine treatments, indicating that PB could improve soil available phosphate content. Adding lysine could strengthen such function.

Isolation, Mutagenesis, and Organic Acid Secretion of a Highly Efficient Phosphate-Solubilizing Fungus.

The highly effective phosphate-solubilizing microorganisms are significant for making full use of the potential phosphorus resources in the soil and alleviating the shortage of phosphorus resources. In this study, a phosphate-solubilizing fungus was isolated from wheat and cotton rhizosphere soils in the lower reaches of the Yellow River in China and was identified as Penicillium oxalicum by morphological and ITS sequencing analysis. In order to obtain a fungus with more efficient phosphorus solubilization ability, we tested three positive mutant strains (P1, P2, and P3) and three negative mutant strains (N1, N2, and N3) through low-energy nitrogen ion implantation mutagenesis. Compared with the parental strain, the phosphate-solubilizing capacity of P1, P2, and P3 was enhanced by 56.88%, 42.26%, and 32.15%, respectively, and that of N1, N2, and N3 was weakened by 47.53%, 35.27%, and 30.86%, respectively. Compared with the parental strain, the total amount of organic acids secreted significantly increased in the three positive mutant strains and decreased in the negative mutant strains; the pH of culture medium was significantly lower in the positive mutant strains and higher in the negative mutant strains. The capacity of phosphate-solubilizing fungus to secrete organic acids and reduce the growth-medium pH was closely related to its phosphate-solubilizing ability. The changes in the amount of organic acids secreted by mutants can alter their acidification and phosphate-solubilizing capacity. In conclusion, this study offers a theoretical basis and strain materials for the exploration and application of phosphate-solubilizing fungi.

Mutation breeding of Aspergillus niger by atmospheric room temperature plasma to enhance phosphorus solubilization ability.

BackgroundPhosphorus (P) is abundant in soils, including organic and inorganic forms. Nevertheless, most of P compounds cannot be absorbed and used by plants. Aspergillus niger v. Tiegh is a strain that can efficiently degrade P compounds in soils.MethodsIn this study, A. niger xj strain was mutated using Atmospheric Room Temperature Plasma (ARTP) technology and the strains were screened by Mo-Sb Colorimetry with strong P-solubilizing abilities.ResultsCompared with the A. niger xj strain, setting the treatment time of mutagenesis to 120 s, four positive mutant strains marked as xj 90–32, xj120–12, xj120–31, and xj180–22 had higher P-solubilizing rates by 50.3%, 57.5%, 55.9%, and 61.4%, respectively. Among them, the xj120–12 is a highly efficient P solubilizing and growth-promoting strain with good application prospects. The growth characteristics such as plant height, root length, and dry and fresh biomass of peanut (Arachis hypogaea L.) increased by 33.5%, 43.8%, 43.4%, and 33.6%, respectively. Besides available P, the chlorophyll and soluble protein contents also vary degrees of increase in the P-solubilizing mutant strains.ConclusionsThe results showed that the ARTP mutagenesis technology can improve the P solubilization abilities of the A. niger mutant strains and make the biomass of peanut plants was enhanced of mutant strains.

Isolation and Screening of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase producing PGPR from Paeonia lactiflora rhizosphere and enhancement of plant growth

Plant growth-promoting rhizobacteria (PGPR) work in a variety of ways to promote plant growth and increase crop yield. They've recently gotten a lot of attention in crops, but not so much in ornamental plants. In this study, 13 PGPR strains containing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase named YDSY1-13 were isolated from the rhizosphere soil of four Paeonia lactiflora cultivars using the medium with ACC as the sole nitrogen source. The ACC deaminase activity, IAA synthesis ability, phosphorus-solubilizing ability, and siderophile production ability of these strains were significantly different, YDSY11 has the highest ACC deaminase activity and YDSY8 has the highest ability to synthesize IAA. The pot experiment showed that inoculation with YDSY8 and YDSY11 dramatically enhanced the photosynthetic capacity, nutrient accumulation, and antioxidant enzyme activity of Paeonia lactiflora. The Petri-dish growth-promoting experiment revealed that PGPR strains boosted Arabidopsis thaliana development, with different strains having different impacts on root morphology, including main root length, number of root tips and lateral roots, and root hair density. Among them, YDSY1, YDSY2, YDSY4, and YDSY8 have the greatest effect on increasing A. thaliana biomass, and the increase in aboveground biomass was positively correlated with that of underground biomass, with the exception of YDSY8. Different strains have diverse growth-promoting abilities based on their growth-promoting characteristics, and this ability is mostly controlled by the combined effect of different growth-promoting characteristics. In addition, we found that the same PGPR may have different growth-promoting mechanisms for different plants. This study provides primary data for the development and utilization of rhizosphere growth-promoting bacteria of P. lactiflora and lays a foundation for further research on the growth-promoting mechanism of PGPR and provides a solution for alleviating fertilizer pollution to the environment.

Relationships between phosphate solubilizing ability, pH, and organic acids of Penicillium oxalicum YTY and its mutants

The high-efficiency phosphate solubilizing mutants of Penicillium oxalicum YTY were screened by mutagenesis of ion beam combined with UV. We analyzed the changes and correlation of phosphate solubilizing ability, pH, and organic acid for YTY and its mutants, and examined the phosphate solubilizing mechanism of P. oxalicum YTY. The results showed that five high-efficiency mutants, P9-8, P9-9, P15-4, P15-6, and P15-7 were screened, and that the phosphate solubili-zing ability of mutants was increased by more than 60% compared with YTY. In the process of pho-sphorus solubilization, both phosphorus solubilizing ability and rate of mutants were higher than that of YTY, and the mutants pH was significantly lower than YTY. The type and content of organic acids secreted by the mutants showed some variations. All mutants and YTY could secrete lactic acid, acetic acid and oxalic acid, while P9-8 also produced citric acid. The pH and the phosphate solubilizing ability of YTY and its mutants had a significant negative correlation. Phosphate solubilizing ability with organic acid and pH were all significantly correlated for YTY and the mutants, except P15-4. Organic acids and low environmental pH reduced by organic acids were the probable mechanism for P. oxalicum to dissolve phosphorus. Radiation of ion beam combined with UV could change the type and content of organic acids of P. oxalicum YTY, and initiate other H+ releasing pathways to lower pH, and participate phosphorus dissolution. The study provided biological mate-rials and theoretical basis for the research and development of high-efficiency phosphate solubilizing P. oxalicum and understanding the phosphate solubilizing mechanism of P. oxalicum.

White rot disease protection and growth promotion of garlic (Allium sativum) by endophytic bacteria

Thirty‐five bacterial isolates, recovered from the healthy bulbs of Allium sativum that grow in different sites of China, were screened for their ability to produce hydrolytic enzymes and metabolites and to dissolve inorganic phosphorus in vitro. These 35 endophytes inhibited the growth of the causal agent of white rot disease, Sclerotium cepivorum (Sc), by 19–64%. The isolates 153 (Bacillus siamensis) (Bs) and 136 (Streptomyces setonii) (Ss) were found to be the most effective in decreasing Sc disease incidence, both by 66%. In addition, there was a significant enhancement in the growth of garlic plants pretreated with isolates 153 Bs and 136 Ss. Isolate 136 could not produce indole‐3‐acetic acid (IAA) and did not exhibit an inorganic phosphorus solubilization ability in vitro. Thus, growth promotion by this Streptomyces sp. is likely to be mediated by a different, and perhaps novel, mechanism to that typically associated with growth promoting bacteria. An increase in expression of alliin lyase 2 was found in garlic plants treated with 153 Bs. By extension, the quantity of the antimicrobial sulphoxide, alliin, was also increased in 153 Bs‐treated and Sc‐inoculated plants, relative to the Sc‐inoculated controls. These results indicated that this bacterial endophyte might protect A. sativum not only by direct antibiosis, but also by enhancing the expression of alliin lyase 2 and the concomitant production of alliin.

Molecular Identification of Rhizospheric Thermo-halotolerant Aspergillus terreus and its Correlation to Sustainable Agriculture

High phosphate solubility is one of the most important factors for increasing plant growth. This study focused on the zinc phosphate (ZP) solubilizing capacity of thermo-halotolerant Aspergillus terreus, where the growth showed halo zones on Pikovskaya agar medium that appeared at high NaCl concentrations (up to 10%) and a wide range of temperatures (up to 45 °C). Acidification of the broth was assumed to be the major mechanism for ZP solubilization by A. terreus, where the growth was related to the pH decrease in the medium containing ZP. Under pot conditions, A. terreus increased the biomass and phosphorus content of Hordeum vulgare plants. A. terreus showed a phosphorus solubilization ability with a NaCl concentration of up to 10%; therefore, A. terreus can be of great benefit in maintaining the available phosphate levels for crops in saline soils. Finally, it was found that A. terreus with ZP can substitute chemical fertilizer and help improve crop production.

Preliminary study on phosphate solubilizing Bacillus subtilis strain Q3 and Paenibacillus sp. strain Q6 for improving cotton growth under alkaline conditions.

BackgroundLow phosphorus availability limits crop production in alkaline calcareous soils in semi-arid regions including Pakistan. Phosphate solubilizing bacteria may improve crop growth on alkaline calcareous soils due to their ability to enhance P availability.MethodsTwenty rhizobacterial isolates (Q1–Q20) were isolated from rhizosphere of cotton and characterized for their growth promoting attributes in vitro. The selected phosphate solubilizing isolates were further screened for their ability to improve cotton growth under axenic conditions (jar trial). The phosphorus solubilization capacities of selected strains were quantified and these strains were identified through 16S rDNA sequencing.ResultsIsolates Q2, Q3, Q6, Q7, Q8, Q13 and Q14 were able to solubilize phosphate from insoluble sources. Most of these isolates also possessed other traits including catalase activity and ammonia production. The growth promotion assay showed that Q3 was significantly better than most of the other isolates followed by Q6. Maximum root colonization (4.34 × 106 cfu g−1) was observed in case of isolate Q6 followed by Q3. The phosphorus solubilization capacities of these strains were quantified, showing a maximum phosphorus solubilization by Q3 (optical density 2.605 ± 0.06) followed by the Q6 strain. The strain Q3 was identified as Bacillus subtilis (accession # KX788864) and Q6 as Paenibacillus sp. (accession # KX788865) through 16S rDNA sequencing.DiscussionThe bacterial isolates varied in their abilities for different growth promoting traits. The selected PGPR Bacillus subtilis strain Q3 and Paenibacillus sp. strain Q6 have multifarious growth promoting traits including ability to grow at higher EC and pH levels, and phosphorus solubilizing ability. These strains can efficiently colonize cotton roots under salt affected soils and help plants in phosphorus nutrition. It is concluded that both strains are potential candidates for promoting cotton growth under alkaline conditions, however further investigation is required to determine their potential for field application.

Growth-Promoting Ability of Rhodopseudomonas palustris G5 and Its Effect on Induced Resistance in Cucumber Against Salt Stress

The objective of this study was to investigate the potential of Rhodopseudomonas palustris G5 in promoting growth and inducing salt resistance in cucumber (Cucumis sativus L.). In this study, the growth-promoting potential of the bacteria was studied by measuring the ability to produce indole-3-acetic acid (IAA) and 5-aminolevulinic acid (ALA), fix nitrogen, and solubilize potassium and phosphate. The greenhouse pot experiments were set up to study how strain G5 affected growth and salt resistance of cucumber seedlings. The results showed that strain G5 exhibited plant growth-promoting attributes such as the production of IAA and ALA, as well as nitrogen-fixing, potassium-solubilizing, and phosphorus-solubilizing ability. In pot trials, strain G5 increased shoot height, root length, fresh weight, dry weight, total chlorophyll content, and soluble sugar content of cucumber seedlings under salt stress, compared to the seedlings that were exposed to salt stress in the absence of the strain G5. Furthermore, antioxidant enzyme activity analysis showed that strain G5 strongly increased the activity of superoxide dismutase, peroxidase, and polyphenol oxidase in cucumber seedlings under salt stress. In addition, strain G5 treatment decreased H2O2 and malondialdehyde contents of salt-stressed seedling. In sum, these results showed that strain G5 enhanced growth and induced systemic resistance in cucumber seedlings under salt stress by the production of IAA, ALA, and soluble sugars, the induction of antioxidant enzymes as well as nutrient adjustment of nitrogen, phosphorus, and potassium.

Isolation of Phosphate Solubilizing Endophytic Fungi From Rice Plant Root

Root endophytic fungi plays different roles for plant, such as plant growth promoting properties, agents to control phytopathogens, and increase phosphorus uptake. Since phosphorus are essential for plant growth and its occurance are limited, so it is necessary to explore these fungus to replace the used of synthetic fertilizer. The objective of this study were to obtain root endophytic fungi from rice plant and to determine its phosphate solubilization ability. The root organ of rice plant was subjected for isolation. Pikovskaya medium was use to determine the fungal phosphorus solubilization ability. Fungal morphological characteristics was carried out by macroscopic and microscopic appearance assessment using microscope. Seven endophytic fungi were successfully isolated from rice plant root sample. Four isolate were micelial steril with no conidia, two isolate refers to Aspergillus and 1 isolate have 2-4 conidia at the tip of conidiophores. Amongs 7 endophytics fungi, only one isolate (P2B3) had the ability to solubilize phosphate with the phosphate solubilization index value 20.45 %.

Isolation and characterization of phosphofungi, and screening of their plant growth-promoting activities

Rhizospheric microorganisms can increase phosphorus availability in the soil. In this regard, the ability of phosphofungi to dissolve insoluble phosphorus compounds is greater than that of phosphate-solubilizing bacteria. The aim of the current study was to identify efficient phosphofungi that could be developed as commercial microbial agents. Among several phosphate-solubilizing fungal isolates screened, strain CS-1 showed the highest phosphorus-solubilization ability. Based on phylogenetic analysis of the internal transcribed spacer region sequence, it was identified as Aspergillus niger. High-performance liquid chromatography analysis revealed that the mechanism of phosphorus solubilization by CS-1 involved the synthesis and secretion of organic acids, mainly oxalic, tartaric, and citric acids. Furthermore, strain CS-1 exhibited other growth-promoting abilities, including efficient potassium release and degradation of crop straw cellulose. These properties help to returning crop residues to the soil, thereby increasing nutrient availability and sustaining organic matter concentration therein. A pot experiment revealed that CS-1 apparently increased the assessed biometric parameters of wheat seedlings, implying the potential of this strain to be developed as a commercial microbial agent. We used Illumina MiSeq sequencing to investigate the microbial community composition in the rhizosphere of uninoculated wheat plants and wheat plants inoculated with the CS-1 strain to obtain insight into the effect of the CS-1 strain inoculation. The data clearly demonstrated that CS-1 significantly reduced the content of pathogenic fungi, including Gibberella, Fusarium, Monographella, Bipolaris, and Volutella, which cause soil-borne diseases in various crops. Strain CS-1 may hence be developed into a microbial agent for plant growth improvement.

Community composition specificity and potential role of phosphorus solubilizing bacteria attached on the different bloom-forming cyanobacteria

The abundance, phosphorus solubilizing ability and community composition of phosphorus solubilizing bacteria (PSB) attached on two bloom-forming cyanobacteria, Microcystis and Anabeana, were investigated in Guanqiao ponds in 2014 and Lake Chaohu in 2015 and 2016. Thirty organic phosphate-mineralizing bacteria (OPB) and eighteen inorganic phosphate-solubilizing bacteria (IPB) isolated from Guanqiao ponds and Lake Chaohu were identified. The community compositions of PSB attached on Microcystis and Anabeana were found to be entirely different. Some PSB were found to be shared by OPB and IPB, especially the species attached on Microcystis, such as Rhizobium sp. Compared to the PSB attached on Anabeana, the PSB attached on Microcystis showed the lower numbers, higher phosphorus solubilizing ability and extensive substrate adaptability. This indicated that the PSB were important for the growth of Microcystis through meeting soluble reactive phosphorus (SRP) demand, which was further supported by the data from Guanqiao ponds where succession process from Anabeana to Microcystis was recorded. All these facts can explain why the succession from Anabeana to Microcystis frequently occurred in shallow eutrophic lakes. Therefore, the attached PSB should be considered as a crucial contributor on algal growth, succession and collapse, depending on algal species.

Phosphate-solubilizing microbes in rhizosphere soils of 19 weeds in southeastern China

Low phosphorus (P) availability is one of the most important factors limiting plant growth in red soils across southeastern China. Many non-symbiotic microorganisms in rhizosphere can enhance P solubility, but little is known about the magnitude of their phosphorus-solubilizing ability (PSA) and the difference in phosphorus-solubilizing microorganisms (PSM) among plant species. The number of phosphorus-solubilizing microorganisms and their PSA in rhizosphere soils of 19 weed species in a citrus orchard on red soil at Changshan. Zhejiang. China, were investigated. Inorganic P (powdered phosphate rock, PR) and organic P (lecithin, OP) were respectively used as the sole P-source to examine the PSA of isolated microbes. The PS actinomycetes community varied greatly among the different weed rhizospheres while the PS fungus community showed to be most stable to the weed rhizosphere. The highest number of PR-PS and OP-PS bacteria was found in rhizosphere soil of Mollugo pentaphyll, and the highest number of PR-PS and OP-PS actinomycetes was found in rhizosphere soil of Polygonum lapathifolium. The highest number of PR-PS fungi was found in Erigeron annuus and Mollugo pentaphyll rhizosphere soil, and the highest number of OP-PS fungi was found in rhizosphere soil of Mazus stachydifolius. Mazus stachydifolius showed the strongest PR-PS ability (6340.75/μg) while Eragrostis pilosa showed the strongest OP-PS ability (1301. 84/μg). The PR-PS ability and OP-PS ability of Mollugo pentaphyll was 4432.87μg and 1122.05μg respectively. A significant correlation between the number of PR-PSM and OP-PSM was found. Significant correlation was only found between the PR-PS fungi number and its PSA (r = 0.75, P<05) and between the number of OP-PS fungi and its PSA (r = 0.87, P<0.01}). It indicated that plant species had significant influence on components of the non symbiotic PSM community and their activity in its rhizosphere soil. Fungi play a leading role in phosphorus solubilization in weed rhizopshere. It suggested that weed conservation could benefit soil microbe development in agroecosystems, especially in the initial stage of agroecosystem development because there is less organic carbon in bare soil. The results suggested that weed conservation could increase PSA of PSM.

Effect of acid phosphatase produced by Trichoderma asperellum Q1 on growth of Arabidopsis under salt stress

Salt stress is a major environmental factor that inhibits crop growth. Trichoderma spp. are the most efficient biocontrol fungi and some of the strains can stimulate plant growth. Phosphate solubilization is known as one of the main mechanisms in promoting plant growth, but the underlying mechanisms of phosphate solubilization in the salinity still need to be explored. The Trichoderma asperellum Q1 isolated and identified in our lab is a beneficial rhizosphere biocontrol fungus with a high phosphate solubilization activity. It could produce acid and alkaline phosphatases when using insoluble organic phosphorus as the sole phosphorus source, the salt stress increased the phosphorus-solubilization ability of the strain and the activities of the two enzymes. Furthermore, an acid phosphatase was purified from the fermentation broth by ammonium sulphate precipitation, ion-exchange, and gel filtration chromatography. Its molecular weight was 55 kDa as determined by SDS-PAGE. The purified acid phosphatase was used to investigate growth performance of Arabidopsis thaliana by plate assay and the result showed that it contributed to Arabidopsis growth by transforming organic phosphate into a soluble inorganic form under salt stress. To our knowledge, this is the first report on acid phosphatase purification from T. asperellum and its function in regulation of plant growth under salt stress.

Potential of Bacillus amyloliquefaciens for Biocontrol of Bacterial Wilt of Tomato Incited by Ralstonia solanacearum

Fifty seven rhizobacteria were isolated from rhizospheric soil of wilted tomato plants and among them two strains of rhizobacteria, having better antagonistic and plant growth promoting ability were characterized them as Bacillus amyloliquefaciens DSBA-11 and DSBA-12 based on morphological, biochemical, partial gene sequence analysis of 16S rRNA and fatty acid methyl ester analysis. Antagonistic activity of these strains DSBA-11, DSBA-12 was compared with other Bacillus species such as B. subtilis DTBS-5, B. cereus JHTBS-7, B. pumilus MTCC-7092 strains, against Ralstonia solanacearum race 1, bv 3, phylotype I, inciting bacterial wilt of tomato underin vitro conditions. B. amyloliquefaciens DSBA-11 showed maximum growth inhibition of R. solanacearum (4.91cm2) followed by strains DSBA-12 (3.31cm2) and B. subtilis (3.07 cm2). Moreover, strains DSBA-11 was also have better phosphorus solubilizing ability (42.6 μg/ml) and indole acetic acid (95.4 μg/ml) production than other strains of Bacillus spp. in vitro conditions. Biocontrol efficacy and plant growth ability of these bacterial antagonists was tested against bacterial wilt of tomato cv. Pusa Ruby under glasshouse conditions. Minimum bacterial wilt disease incidenceincultivar Pusa Ruby (17.95%) was recorded in B. amyloliquefaciens DSBA-11followed by B. amyloliquefaciens DSBA-12 after 30 days of inoculation.The bio-control efficacy was higher in B. amyloliquefaciens DSBA -12 treated plants, followed by B. pumilus MTCC- 7092.