Ethyl Methanesulfonate Mutagenesis–Enhanced Mineral Phosphate Solubilization by Groundnut-Associated <Emphasis Type="Italic">Serratia marcescens</Emphasis> GPS-5

Twenty-three bacterial isolates were screened for their mineral phosphate–solubilizing (MPS) ability on Pikovskaya and National Botanical Research Institute’s phosphate (NBRIP) agar. The majority of the isolates exhibited a strong ability to solubilize hydroxyapatite in both solid and liquid media. The solubilization in liquid medium corresponded with a decrease in the pH of the medium. Serratia marcescens GPS-5, known for its biocontrol of late leaf spot in groundnut, emerged as the best solubilizer. S. marcescens GPS-5 was subjected to ethyl methanesulfonate (EMS) mutagenesis, and a total of 1700 mutants, resulting after 45 minutes of exposure, were screened on buffered NBRIP medium for alterations in MPS ability compared with that of the wild type. Seven mutants with increased (increased-MPS mutants) and 6 mutants with decreased (decreased-MPS mutants) MPS ability were isolated. All seven increased-MPS mutants were efficient at solubilizing phosphate in both solid and liquid NBRIP medium. Among the increased-MPS mutants, EMS XVIII Sm-35 showed the maximum (40%) increase in the amount of phosphate released in liquid medium compared with wild-type S. marcescens GPS-5, therefore, it would be a useful microbial inoculant in groundnut cultivation. EMS III Sm W, a nonpigmented mutant, showed the lowest solubilization of phosphate among the 6 decreased-MPS mutants.     

Characterization of the mineral phosphate solubilizing activity of <Emphasis Type="Italic">Serratia marcescens</Emphasis> CTM 50650 isolated from the phosphate mine of Gafsa

The mineral phosphate solubilizing (MPS) ability of a Serratia marcescens strain, namely CTM 50650, isolated from the phosphate mine of Gafsa, was characterized on a chemically defined medium (NBRIP broth). Various insoluble inorganic phosphates, including rock phosphate (RP), calcium phosphate (CaHPO₄), tri-calcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite were tested as sole sources of phosphate for bacterial growth. Solubilization of these phosphates by S. marcescens CTM 50650 was very efficient. Indeed, under optimal conditions, the soluble phosphorus (P) concentration it produced reached 967, 500, 595 and 326 mg/l from CaHPO₄, Ca₃(PO₄)₂, hydroxyapatite and RP, respectively. Study of the mechanisms involved in the MPS activity of CTM 50650, showed that phosphate solubilization was concomitant with significant drop in pH. HPLC-analysis of culture supernatants revealed the secretion of gluconic acid (GA) resulting from direct oxidation pathway of glucose when the CTM 50650 cells were grown on NBRIP containing glucose as unique carbon source. This was correlated with the simultaneous detection by PCR for the first time in a S. marcescens strain producing GA, of a gene encoding glucose dehydrogenase responsible for GA production, as well as the genes pqqA, B, C and E involved in biosynthesis of its PQQ cofactor. This study is expected to lead to the development of an environmental-friendly process for fertilizer production considering the capacity of S. marcescens CTM 50650 to achieve yields of P extraction up to 75% from the Gafsa RP.     

Isolation,Selection and Characterization of Root-Associated Rock Phosphate Solubilizing Bacteria in Moroccan Wheat (Triticum aestivum L.)

Abstract

Phosphorus (P) is the most important macronutrient next to nitrogen for the growth and development of plants. But often unavailable for plants because of its high reactivity with many soil constituents. Thus, the use of phosphate solubilizing bacteria (PSBs) as biofertilizers seems to be an effective way to resolve the soluble phosphorus availability in soil. The present study was conducted to isolate and characterize rock PSB associated with the rhizosphere of wheat (Triticum aestivum L.) from fourteen different wheat-growing sites of Meknes region in Morocco. A total of one hundred ninety-eight (198) rock PSBs were isolated employing NBRIP medium amended with rock phosphate (RP), out of which five strains (A17, A81, B26, B106, and B107) were selected for their strong ability to dissolve RP and were tested in vitro for plant growth-promoting (PGP) traits including production of indole acetic acid (IAA), siderophores, hydrogen cyanide (HCN), and antifungal activity, as well as their response to the effect of extrinsic and intrinsic stress. The 16S rRNA gene sequencing and phylogenetic analysis identified these isolates belong to four genera, Pantoea, Pseudomonas, Serratia, and Enterobacter. The phosphate solubilization index (SI) of selected isolates ranged between 2.3 and 2.7, and the amount of solubilized phosphorus in the liquid medium varied from 59.1 to 90.2 µg mL^?1. HPLC analysis revealed that all the selected isolates produced multiple organic acids (oxalic, citric, gluconic succinic, and fumaric acids) from glucose under aerobic conditions. Except for the A81 strain, all selected isolates were able to produce IAA ranging between 2.9 and 21.2 µg mL^?1. The isolates A17, B26, and B107 showed the ability to produce siderophores ranging from 79.3 to 20.8% siderophore units. Only two strains (A17 and B26) were able to produce HCN. All selected isolates showed good resistance against different environmental stresses like 10–50?°C temperature, 0.5–2?g L^?1 salt concentration and 4.5–9?pH range, and against different antibiotics. The antagonistic effect showed that among the five selected strains, only two strains (B26 and A17) were able to suppress the growth of tested fungi. This study clearly indicates that our selected rock PSBs can be used as biofertilizers for grain crops after studying their interaction with the host crop and field evaluation.     

Effect of Carbon Substrates on Rock Phosphate Solubilization by Bacteria from Composts and Macrofauna

Five of the 207 isolates from different composts, farm waste compost (FWC), rice straw compost (RSC), Gliricidia vermicompost (GVC), and macrofauna, showed rock phosphate (RP) solubilization in buffered medium in plate culture. When tested in RP broth medium, all five strains, Enterobacter cloacae EB 27, Serratia marcescens EB 67, Serratia sp. EB 75, Pseudomonas sp. CDB 35, and Pseudomonas sp. BWB 21, showed gluconic acid production and solubilized RP. Based on cellulose-degrading and P-solubilizing ability, two strains were selected for further studies. In the presence of different carbon sources, both strains showed a drop in pH and solubilized RP. P released was maximum with glucose (1212 and 522 μmol) and minimum with cellobiose (455 and 306 μmol) by S. marcescens EB 67 and Pseudomonas sp. CDB 35, respectively. Glucose dehydrogenase (GDH) activity was 63 and 77% with galactose and 35 and 46% with cellobiose when compared to glucose (100%) by EB 67 and CDB 35, respectively. Both strains solubilized RP in the presence of different crop residues. EB 67 and CDB 35 showed maximum cellulase activity (0.027 units) in the presence of rice straw and a mixture of rice straw and root. P solubilized from RP in the presence of pigeonpea root was 134 and 140 μmol with EB 67 and CDB 35. Significantly, these bacteria isolated from composts and macrofauna solubilized rock phosphate in the presence of various pure carbon substrates and crop residues and their importance in soil/rhizosphere conditions is discussed.     

Isolation and characterisation of phosphate solubilising microorganisms from the cold desert habitat of <Emphasis Type="Italic">Salix alba Linn.</Emphasis> in trans Himalayan region of Himachal Pradesh

Phosphate solubilising microorganisms (PSM) (bacteria and fungi) associated with Salix alba Linn. from Lahaul and Spiti valleys of Himachal Pradesh were isolated on Pikovskaya (PVK), modified Pikovskaya (MPVK) and National Botanical Research Institute agar (NBRIP) media by spread plating. The viable colony count of P-solubilising bacteria (PSB) and fungi (PSF) was higher in rhizosphere than that of non-rhizosphere. The frequency of PSM was highest on MPVK followed by NBRIP and PVK agar. The maximum proportion of PSM out of total bacterial and fungal count was found in upper Keylong while the least in Rong Tong. The PSB frequently were Gram-positive, endosporeforming, motile rods and belonged to Bacillus sp. The PSF mainly belonged to Penicillium sp., Aspergillus fumigatus, A. niger, A. spp. and non-sporulating sterile. Amongst the isolates with high efficiency for tricalcium phosphate (TCP) solubilisation, seven bacterial and seven fungal isolates dissolved higher amount of P from North Carolina rock phosphate (NCRP) than Mussoorie rock phosphate (MRP) and Udaipur rock phosphate (URP). However, the organisms solubilised higher-P in NBRIP broth than PVK broth. SBC5 (Bacillus sp.) and SBC7 (Bacillus sp.) bacterial isolates exhibited maximun P solubilisation (40 and 33 μg ml⁻¹ respectively) whereas FC28 (Penicillium sp.) isolate (52.3 μg ml⁻¹) amongst fungi while solubilising URP. The amount of P solubilised was positively correlated with the decrease in pH of medium. SBC5 (Bacillus sp.), SBC7 (Bacillus sp.) and SBC4 (Micrococcus) decreased the pH of medium from 6.8 to 6.08 while FC28 (Penicillium sp.) and FC39 (Penicillium sp.) isolates of fungi recorded maximum decrease in pH of medium from 6.8 to 5.96 in NBRIP broth.     

Solubilization of Morocco phosphorite by Aspergillus niger

Phosphorus containing fertilizers have an important role in agriculture. Conventionally phosphate fertilizers are obtained by rock phosphate (RP) dissolution using mineral acids. Biotechnological methods can be a promising alternative in RP processing. The influence of Aspergillus niger strain, the composition of a nutritive medium, Morocco phosphorite (MP) concentration in the liquid medium, the time of bioconversion and the preliminary mechanical activation (PMA) of MP on the phosphorite microbial solubilization has been presented. The phosphorus concentration (as P2O5), citric acid production, glucose concentration and pH in the cultural medium were monitored. The phosphate concentration was expressed as water soluble - alpha1 (in the native cultural liquid), citrate soluble - alpha2 (after treating the biomass and remaining mineral mass with citric acid) and biomass available phosphorus - alpha3. Phosphate dissolution was not strongly correlated both with the citric acid production and the incubation period. When the fungi were grown without water soluble phosphorus compounds the MP solubilization had higher values. A maximum of 94.80% total P2O5 extraction was achieved. The PMA activity does not facilitate MP dissolution during the bioconversion.     

一株高效解磷菌的筛选鉴定及溶磷性能

【背景】土壤中大部分磷元素是以难溶性磷酸盐的形式存在,不能被农作物有效利用,而传统化学肥料会带来环境污染等问题。【目的】解决土壤磷缺失现状,开发新型、安全、高效的微生物菌肥。【方法】取武汉科技大学图书馆后土壤为试验材料,筛选出一株高效解磷菌。通过个体形态鉴定、生理生化鉴定、16S rRNA基因序列分析鉴定菌株,以NBRIP为基础培养基进行条件优化,借助高效液相色谱进行细菌解磷机理探究。【结果】所筛选的高效解磷菌株为唐菖蒲伯克霍尔德氏菌(Burkholderia gladioli)。在20种氨基酸中,D-蛋氨酸对菌株的生长和溶磷促进作用最好,促进效果达到19.09%和16.16%,甲酸钠对菌株的生长和溶磷有抑制效果,抑制效果达到39.08%和10.66%。该菌株通过分泌葡萄糖醛酸、D-L-苹果酸等有机酸溶解环境中的磷酸盐,将菌株制作成菌肥对辣椒幼苗有明显的促生长作用。【结论】利用唐菖蒲伯克霍尔德氏菌(Burkholderia gladioli)分泌有机酸溶解土壤中的磷酸盐,可为生物肥料的制备和应用提供一定的理论参考。     

Biochar Enhances Aspergillus niger Rock Phosphate Solubilization by Increasing Organic Acid Production and Alleviating Fluoride Toxicity

During fungal rock phosphate (RP) solubilization, a significant quantity of fluoride (F⁻) is released together with phosphorus (P), strongly inhibiting the process. In the present study, the effect of two F⁻ adsorbents [activated alumina (Al₂O₃) and biochar] on RP solubilization by Aspergillus niger was examined. Al₂O₃ adsorbed part of the F⁻ released but also adsorbed soluble P, which makes it inappropriate for microbial RP solubilization systems. In contrast, biochar adsorbed only F⁻ while enhancing phosphate solubilization 3-fold, leading to the accumulation of up to 160 mg of P per liter. By comparing the values of F⁻ measured in solution at the end of incubation and those from a predictive model, it was estimated that up to 19 mg of F⁻ per liter can be removed from solution by biochar when added at 3 g liter⁻¹ to the culture medium. Thus, biochar acted as an F⁻ sink during RP solubilization and led to an F⁻ concentration in solution that was less inhibitory to the process. In the presence of biochar, A. niger produced larger amounts of citric, gluconic, and oxalic acids, whether RP was present or not. Our results show that biochar enhances RP solubilization through two interrelated processes: partial removal of the released F⁻ and increased organic acid production. Given the importance of organic acids for P solubilization and that most of the RPs contain high concentrations of F⁻, the proposed solubilization system offers an important technological improvement for the microbial production of soluble P fertilizers from RP.     

杨树根际解无机磷细菌Mp1-Ha4的鉴定及其解磷机理

解无机磷细菌能够溶解土壤中的难溶性磷酸盐,增加土壤有效磷含量,促进植物生长。以一株杨树根际土壤中筛选得到的解无机磷细菌Mp1-Ha4为研究对象,利用分子生物学的方法对该菌株进行鉴定,测定了其对磷酸钙、磷酸铝和磷酸铁的解磷能力,并对该菌株9 d内的磷酸钙溶解动力学进行了研究。结果表明,解无机磷细菌Mp1-Ha4为一株西地西菌Cedecea sp.,其对磷酸钙的溶解能力远强于对磷酸铝和磷酸铁的溶解能力。在NBRIP液体培养基中,该菌株对磷酸钙的溶解能力达到了497.4 mg/L,在其对磷酸钙解磷过程中,培养基pH及可滴定酸度与解磷量分别呈显著负、正相关。高效液相色谱分析显示,该菌株在解磷过程中分泌了大量有机酸,主要包括α-酮戊二酸,酒石酸和苹果酸。分泌有机酸,降低环境pH可能是解无机磷细菌西地西菌(Cedecea sp.)Mp1-Ha4溶解难溶性磷酸盐的主要机制,同时该菌株对磷酸钙的高效溶解作用使其具有较大的研究和应用前景。     

Enhanced solubilization of rock phosphate by Penicillium bilaiae in pH-buffered solution culture

Little is known about how pH-buffering capacity affects phosphorus (P) solubilization by Penicillium bilaiae. This study compared solubilization of rock phosphate (RP) by P. bilaiae in nonbuffered (pH 5.0) and buffered (pH 7.0) media. Fungal growth reached the stationary phase around day 12 and was slightly enhanced in the buffered medium. The fungus reduced solution pH from 5.0 to 4.1 in the nonbuffered medium and from 7.0 to 4.9 in the buffered medium by day 12. Phosphorus concentrations increased after day 9 more in the buffered than in the nonbuffered media (53 and 5 mg P x L(-1), respectively, on day 12). On day 12, higher concentrations of citric and oxalic acids were detected in the buffered (2.0 and 1.2 g x L(-1), respectively) than nonbuffered media (0.5 and 0.04 g x L(-1), respectively). Solubilization of RP was simulated without P. bilaiae in solutions equivalent to the nonbuffered and buffered cultures of P. bilaiae grown with RP. After a 24 h incubation, the P concentrations were of similar magnitudes to those observed in the P. bilaiae culture (18 and 47 mg P x L(-1), respectively, in the nonbuffered and buffered media). Under increased pH-buffering conditions, the enhanced production of citric and oxalic acids led to significant RP solubilization.     

4种外生菌根真菌对难溶性磷酸盐的溶解能力

以红绒盖牛肝菌(Xerocomus chrysenteron)、美味牛肝菌(Boletus edulis)、黄须腹(Rhizopogen luteous)和劣味乳菇(Lactarius insulsus)4种外生菌根真菌为对象,在纯培养条件下比较它们对4种难溶性磷酸盐[Ca_3(PO_4)_2、Ca_(10)(PO_4)_6(OH)_2、FePO_4·4H_2O和AlPO_4]的溶解能力,以探讨外生菌根真菌对难溶性磷酸盐的溶解作用及其影响因素.结果表明:(1)4种外生菌根真菌均能在Ca_3(PO_4)_2为唯一磷源的NBRIP平板上生长,但生长速率明显不同,且红绒盖牛肝菌生长速率最快.(2) 4种菌根真菌对4种磷酸盐的溶解能力存在显著差异,红绒盖牛肝菌发酵液可溶性磷含量大多显著高于对照和其他菌根真菌,对磷酸盐的溶解能力最强.(3)4种菌根真菌发酵液可滴定酸度(2.30～46.00 mmol·L~(-1))和pH(4.57～6.99)与其溶磷量分别呈极显著正相关(r=0.991**)和极显著负相关(r=-0.939**).(4)4种外生菌根真菌均能分泌乙酸、柠檬酸和反丁烯二酸,且它们分泌有机酸总量(14.14～1 537.46 mg·L~(-1))与其溶磷量呈显著正相关(r=0.998*).研究发现, 4种外生菌根真菌发酵液可滴定酸度、pH和有机酸的种类与含量是影响其溶解Ca_3(PO_4)_2能力的主要因素;红绒盖牛肝菌的溶磷能力较强,具有应用于中国土壤缺磷地区造林的潜力.     

Interaction of phosphorus fertilizer form and soil medium on Douglas-fir seedling phosphorus content,growth and photosynthesis

Douglas-fir seedlings were grown in containers in peat-vermiculite or mineral soil each amended with different levels of concentrated superphosphate (CSP) or a granulated North Carolina phosphate rock (RP). Media dilute acid-fluoride extractable phosphorus (DAP), seedling photosynthesis, weights, and tissue P concentrations were measured at 65±3 and 105±3 days. DAP was highly correlated with soluble fertilizer P (but not total P) added at the beginning of the experiment. Considerable soluble P was lost from peat-vermiculite but not from the mineral soil. Seedling total P content was proportional to the amount of soluble P per container at both harvests, but was greater for a given level of soluble P in the organicversus the mineral medium. Added soluble P increased foliar P concentrations, plant P content, and dry weight. Net carbon uptake was highly correlated with added levels of soluble P, foliar P concentrations, and with total P content. The internal efficiency of P from the RP source was less than P from CSP with respect to P contentversus growth, net CO₂ uptake, and net photosynthesis rates. At the end of the experiment, seedling P content plus DAP remaining in the media for the higher fertilizer rates accounted for 75% of the originally added soluble P in the mineral soils, but only 15% of the originally added soluble P in the organic media.     

Development of Iron-Phosphate Biofilms on Pyritic Mine Waste Rock Surfaces Previously Treated with Natural Phosphate Rocks

Various treatments have been proposed to attenuate and eventually inhibit the generation of acid mine drainage (AMD) or acid-rock drainage (ARD). The addition of Natural Phosphate Rocks (NPR) to mining wastes has been shown to reduce acid generation. The biogeochemical reactions underlying the phosphate precipitation reactions are however poorly understood, even though the chemical reactions are well defined. The present study was designed to study the role of solution chemistry and bacterial activity on phosphate precipitation on waste rock surfaces. Waste rock samples (rich in sulphides) previously weathered for 989 days in the presence of NPR were submersed in 2 different phosphate-rich growth media in order to enhance the growth of acidophilic and neutrophilic bacteria. DAPI and FISH analyses revealed that most cells belonged to the bacteria domain, and that alpha- and beta-proteobacteria were the dominant neutrophiles. ESEM, SEM and TEM observations of the samples revealed the presence of a biofilm on the surface of the rocks at both pH conditions. Bacteria and fine-grained precipitates were trapped in an exopolymer matrix. At low pH, the formation of fine precipitates rich in Fe and P within the biofilm corresponded to a decline of phosphate concentrations in the growth medium. This was in agreement with the solubility calculations which indicated that the medium became over-saturated with respect to some Fe-phosphate minerals. In the pH neutral system, solubility calculations indicated that Ca- and Mg-phosphate minerals were stable, but they were not detected in the biofilm. Solubility calculations also indicated that vivianite became unstable over time, which could explain the release of soluble phosphate over time in the pH neutral system. Our results showed that precipitation reactions played an important role in the solubility of phosphate in both systems, but a series of complex nucleation reactions involving bacterial exopolymers and the presence of microenvironments within the biofilms were likely important factors as well. Our findings also imply that the reduction of acid generation in NPR-treated waste rocks could be due in part to the formation of biofilms on the rock surfaces because the biofilms would act as a physical and chemcial barrier to limit the extent of pyrite oxidation.     

Optimizations of particle size and pulp density for solubilization of rock phosphate by a microbial consortium from activated sludge

Microbial solubilization of rock phosphate is getting more and more attention recently. However, the microorganisms used in previous studies were mostly single or known species, and seldom studies focused on the mixed microorganisms or microbial consortia from natural environments. In this study, a microbial consortium taken from activated sludge was used to solubilize two different mid-low-grade rock phosphates. The results showed that the microbial consortium could effectively solubilize the rock phosphates in National Botanical Research Institute’s phosphate growth medium and released soluble phosphorus in the broth. The biomass increased gradually, whereas the pH decreased sharply during the solubilizing process. The maximum phosphorus solubilization was recorded at particle size of 150?µm. Higher or lower than this optimal particle size, the phosphorus solubilization decreased. The phosphorus solubilization gradually decreased with a larger pulp density from 1 to 5%, and the optimal pulp density was 1%. The solubilization level of microbial consortium varied with different rock phosphates. The results revealed that the soluble phosphorus released from high-silicon ore was higher than which from high-magnesium ore. A strong positive correlation between biomass and phosphorus solubilization in the broth was observed from regression analysis results, and the phosphorus solubilization also had a significant negative correlation with pH in the broth.     

Dissolution of Fluorapatite by Pseudomonas fluorescens P35 Resulting in Fluorine Release

Chemical weathering of fluorine-bearing minerals is widely accepted as the main mechanism for the release of fluorine (F) to groundwater. Here, we propose a potential mechanism of F release via microbial dissolution of fluorapatite (Ca₅(PO₄)₃F), which has been neglected previously. Batch culture experiments were conducted at 30°C with a phosphate-solubilizing bacteria strain, Pseudomonas fluorescens P35, and rock phosphates as the sole source of phosphate for microbial growth in parallel with abiotic controls. Rock phosphates consisted of 55–91% of fluorapatite and 5–10% of dolomite before microbial dissolution as indicated by X-ray diffraction (XRD). Mineral composition and morphology changed after microbial dissolution characterized by the disappearance of dolomite and the development of etched cavities on rock phosphate surfaces. The pH of media used was approximately 7.4 at the beginning and increased gradually to 7.7 in abiotic controls; with the inoculum, the pH decreased to acidic values of 3.7–3.8 after 27 h. Phosphate, calcium, and fluoride were released from the rock phosphate to the acidified medium. At 42 h, the concentration of F reached 8.1–10.3 mg L^?1. The elevated F concentration was two times higher than the F levels in groundwater in regions diagnosed with fluorosis, and was toxic to the bacteria, as demonstrated by a precipitous decrease in live cells. Geochemical modeling demonstrated that the oxidation of glucose (the carbon source for microbial growth in the medium) to gluconic acid could decrease the pH to 3.7–3.8 and result in the dissolution of fluorapatite and dolomite. Dolomite and fluorapatite remained unsaturated, while concentrations of dissolved phosphorus (P), calcium (Ca), and F increased throughout the time course Fluorite reached saturation [saturation index (SI) 0.22–0.42] after 42 h in rock phosphate–amended biotic systems. However, fluorite was not detected in XRD patterns of the final residue from microcosms. Given that phosphate-solubilizing bacteria are ubiquitous in soil and groundwater ecosystems, they could play an important role in fluorapatite dissolution and the release of F to groundwater.     

黑曲霉解磷能力的影响因素及培养条件优化

本文探讨了培养条件下黑曲霉解磷能力的主要影响因素。通过单孢株筛选得到解磷能力较强的菌株Xj-2,其在液体培养基中的解磷能力达到539.90 mg·L^-1。解磷发酵动力学模型模拟发现,其解磷能力在培养的第4 天达到平稳,可作为终止发酵时间。不同磷源培养液中菌株Xj-2的解磷量依次为磷酸钙(539.90 mg·L^-1)>磷酸锌(238.45 mg·L^-1)>磷酸铁(182.64 mg·L^-1)>磷矿粉(71.80 mg·L^-1)>磷酸铝(24.40 mg·L^-1)。通过单因素试验并结合响应面优化,研究了其解磷最佳条件。结果表明: 碳源对Xj-2的解磷能力影响最大,其次是菌群密度和培养液pH。当培养温度35 ℃、转速160 r·min^-1、培养液pH 6.0、氮源(尿素)浓度0.79 g·L^-1、碳源(葡萄糖)浓度10.00 g·L^-1、菌群密度3.8%、培养时间为4 d时,Xj-2的解磷能力最高,为616.81 mg·L^-1。     

Factors determining rock phosphate solubilization by microorganisms isolated from soil

Forty two soil isolates (31 bacteria and 11 fungi) were studied for their ability to solubilize rock phosphate and calcium phosphate in culture medium. Eight bacteria and 8 fungi possessed solubilizing ability. Pseudomonas cepacia and Penicillium purpurogenum showed the highest activity. There was a correlation between final pH value and titratable acidity (r=–0.29 to –0.87) and between titratable acidity and soluble phosphate (r=0.22 to 0.99). Correlation values were functions of insoluble phosphate and of the group of microorganisms considered. A high correlation was observed between final pH and soluble phosphate only for the rock phosphates inoculated with the highest concentration of solubilizing bacteria (r=–0.73 to –0.98).     

Enhancement and Cultural Characteristics of Leucomycin Production by Streptomyces kitasatoensis in the Presence of Magnesium Phosphate

Stimulation of leucomycin production with Streptomyces kitasatoensis by magnesium phosphate (MgP), and a concomitant decrease of ammonium ion concentration in the culture supernatant have been reported from this laboratory. Cultural characteristics of the MgP-supplemented culture were further examined in relation to the stimulation of leucomycin production. When the leucomycin titer increased 4- to 5-fold in the presence of MgP, mycelial growth level and assimilation rate of a major carbon source (glycerol) increased about 2-fold. MgP-grown mycelia were not appreciably different in shape or in carbon and nitrogen contents from the control mycelia. Magnesium and phosphate ions were released from MgP into the medium, while the addition of magnesium or phosphate salts to the control medium was rather inhibitory for leucomycin production. The pH values of MgP-supplemented cultures were lower than those of the control culture. When modifications of the basal media and culture conditions were done so as to permit the pH-change almost identical with that of the control media, the leucomycin titer was still higher in the presence of MgP than in its absence. When uric acid, an insoluble compound, was used as the sole nitrogen source, the leucomycin production increased to a high level even in the absence of MgP, which was comparable to that seen when MgP was added to the ammonium lactate-containing medium. The ammonium ion concentration in the culture supernatant of the uric acid-containing medium was maintained at a considerably low level. While in the ammonium lactate-containing medium, leucomycin production was low and ammonium ion concentration remained at a high level. Thus, it was demonstrated that the stimulation of leucomycin production by MgP is related to the lowering of ammonium ion level, but not to the other factors examined such as growth level, carbon or phosphate regulation and pH-effect.     

Rock phosphate solubilization by four yeast strains

The solubilization of rock phosphate (RP) by four yeast strains, Rhodotorula sp., Candida rugosa, Saccharomyces cerevisiae and Saccharomyces rouxii, which were isolated from wheat rhizospheric soils, was investigated in this study. The yeast isolates demonstrated diverse levels of soluble phosphate releasing abilities in modified Pikovskaya liquid medium containing RP as sole phosphate source. C. rugosa was the most effective solubilizer under different conditions, followed by Rhodotorula sp., S. rouxii and S. cerevisiae. Acidification of the broth seemed to be the major mechanism for RP solubilization by the yeast isolates, and the increase in soluble phosphate released was correlated significantly with an increase in titratable acidity and a drop in pH. The optimal composition for the solubilization of RP by the yeast isolates in the broth was 20 g L^?1 glucose, 1 g L^?1 yeast extract, 0.5 g L^?1 (NH₄)₂SO₄, and 5 g L^?1 RP, respectively. The yeast isolates were able to solubilize RP at wide range of temperature and initial pH, with the maximum percentage of soluble phosphate released being recorded at 30–35 °C and pH 5–6, respectively.     

稻、麦根系H~ 的分泌与介质磷水平的关系

水稻、小麦根系H~ 的分泌量随供磷水平的降低而增加,并存在明显的昼夜变化。在自然光照下H~ 分泌量随光强度增加而增多,同时强光比黑暗时H~ 分泌对磷供应水平更为敏感。磷供应不足还诱导水稻根系柠檬酸分泌量增加,而苹果酸则差异不明显。难溶性磷的溶解率与根系H~ 和柠檬酸分泌所导致的根际pH下降有密切联系。因此,在有效磷不足的条件下可明显提高稻、麦根际土壤中难溶性磷的利用率,其中丰产型小麦和粳稻品种对土壤中磷利用的根际效应更为显著。