Growth, Fe3+ Reductase Activity, and Siderophore Production by Paenibacillus polymyxa SQR-21 Under Differential Iron Conditions

An experiment was planned to evaluate the behavior of Paenibacillus polymyxa SQR-21 under differential iron availability. P. polymyxa was grown under three differential iron conditions (0, 2, 20 μM). Iron starvation slowed bacterial growth and at all iron levels, pH of liquid culture was decreased, but maximum decrease was observed at highest iron level. Cell surface ferrireductase activity decreased as culture aged, while extracellular Fe³⁺-reducing activity constantly increased. Hydroxamates type siderophores production was increased with the decrease in iron levels. Numerous cellular proteins were expressed by P. polymyxa in the range of 5–140 kDa and several of them showed conspicuous differential iron regulation. P. polymyxa seems to have more than one type of iron acquisition mechanism including gradual release of organic acids, cell surface ferrireductases, extracellular reductants, and secretion of low molecular weight hydroxamates chelators. This article is the first to report the kinetic study of P. polymyxa under differential iron availability. The information provided here gives initial information about the iron uptake mechanism of P. polymyxa.     

Bacterial Growth Stimulation with Exogenous Siderophore and Synthetic N-Acyl Homoserine Lactone Autoinducers under Iron-Limited and Low-Nutrient Conditions

The growth of marine bacteria under iron-limited conditions was investigated. Neither siderophore production nor bacterial growth was detected for Pelagiobacter sp. strain V0110 when Fe(III) was present in the culture medium at a concentration of <1.0 μM. However, the growth of V0110 was strongly stimulated by the presence of trace amounts of exogenous siderophore from an alpha proteobacterium, V0902, and 1 nM N-acyl-octanoylhomoserine lactone (C₈-HSL), which is known as a quorum-sensing chemical signal. Even though the iron-binding functionality of a hydroxamate siderophore was undetected in the supernatant of V0902, a hydroxamate siderophore was detected in the supernatant of V0110 under the above conditions. These results indicated that hydroxamate siderophore biosynthesis by V0110 began in response to the exogenous siderophore from V0902 when in the presence of C₈-HSL; however, C₈-HSL production by V0110 and V0902 was not detected. Direct interaction between V0902 and V0110 through siderophore from V0902 was observed in the dialyzing culture. Similar stimulated growth by exogenous siderophore and HSL was also observed in other non-siderophore-producing bacteria isolated from marine sponges and seawater. The requirement of an exogenous siderophore and an HSL for heterologous siderophore production indicated the possibility that cell-cell communication between different species was occurring.     

Cd2+结合肽的筛选及与重金属离子的亲和作用

利用噬菌体随机十二肽库和亲和层析技术对重金属Cd进行亲和筛选,共获得两条Cd结合肽序列。将展示有Cd2 结合肽的噬菌体单克隆扩增物对不同重金属离子(Cd2 、Cr2 、Cu2 、Co2 、Zn2 、Ni2 )螯合的树脂进行亲和测定,结果表明Cu2 、Co2 、Zn2 、Ni2 对结合肽的亲和力高于Cd2 和Cr2 。抑菌解毒试验进一步确认了Cd2 结合肽对大肠杆菌重金属的解毒作用。显微观察可见金属结合肽与金属螯合树脂混合后分散度发生改变。     

Isolation and Identification of Three Potassium-Solubilizing Bacteria from Rape Rhizospheric Soil and Their Effects on Ryegrass

More than 90% of potassium (K) in soil exists in forms of insoluble silicate minerals and cannot be directly utilized by plants. K-solubilizing bacteria (KSB) can improve soil fertility and plant growth as biofertilizers by decomposing silicate minerals and releasing insoluble K into soluble forms. The objectives of this study were to isolate and characterize KSB from rape rhizospheric soil and to evaluate their effects on ryegrass growth. In this study, 16 cultivable potential KSB were isolated from rape rhizosphere at first. Then, quantitative analysis revealed that three KSB strains, named S-15, S-17 and S-18, showed the best K mineral solubilizing ability and they were identified as Mesorhizobium sp., Paenibacillus sp. and Arthrobacter sp. Inoculating the three strains into available K limit soil increased available K content significantly. The result of the pot experiment revealed that the three strains increased ryegrass growth vigor, biomass yield and K uptake to different degrees in available K deficient soil. S-17 showed the most pronounced ryegrass growth promotion ability. Further studies are required to determine the effects of the three KSB on mobilization of K-bearing minerals under field conditions.     

Increasing of Soil Urease Activity by Stimulation of Indigenous Bacteria and Investigation of Their Role on Shear Strength

Abstract

Recent studies have shown that the use of biostimulation is an effective technique to eliminate the environmental side effects of traditional soil improvement methods. The use of indigenous bacteria of soil is a new method through which indigenous bacteria produce carbonate calcium by their urease activity. Stimulation of soil indigenous bacteria with the aim of calcite precipitation can considerably increase the soil shear strength. In this study, indigenous ureolytic bacteria are stimulated by adding nutrients to the soil. Subsequently urease activity of these bacteria in the presence of calcium chloride and nickel chloride causes calcium carbonate to precipitate between the sand particles. The analysis showed that the stimulated soil compared to the control soil was significantly different in terms of the soil engineering properties and the amount of precipitated calcite. Further, the treated and untreated samples were examined using direct shear test, scanning electron microscope (SEM), and energy dispersive X-ray (EDX) analysis. The results showed an increase of 30–67% in ultimate shear strength, 4–18.8% in residual shear strength, 190% in the cohesion intercept, and 16.8% in the angle of internal friction. In addition, imaging and analysis of SEM-EDX indicated the production of large amounts of calcite precipitates on surfaces of soil particles and between them.     

Fe and P Solubilization Under Limiting Conditions by Bacteria Isolated from Carex kobomugi Roots at the Hasaki Coast

Our objective was simply to report a sedge species, Carex kobomugi Ohwi that has beneficial bacterial associations under low Fe and P conditions of the Hasaki coast, Japan. C. kobomugi is the dominant species in our study area and grows closest to the sea. C. kobomugi showed higher Fe and P content, while these nutrients were less available under alkaline root-zone soil. Within the roots, mycorrhizal fungal colonization was absent, and endophytic fungal colonization was low. On the contrary, endophytic bacteria (e.g. Bacillus sp., Streptomyces luteogriseus, and Pseudomonas fluorescens) were isolated, which exhibited both siderophore production and inorganic phosphate solubilization under Fe or P limited conditions. Our results suggest that colonization of root tissue by these bacteria contribute to the Fe and P uptakes by C. kobomugi by increasing availability in the soil.     

Coral-Associated Bacteria and Their Role in the Biogeochemical Cycling of Sulfur

Marine bacteria play a central role in the degradation of dimethylsulfoniopropionate (DMSP) to dimethyl sulfide (DMS) and acrylic acid, DMS being critical to cloud formation and thereby cooling effects on the climate. High concentrations of DMSP and DMS have been reported in scleractinian coral tissues although, to date, there have been no investigations into the influence of these organic sulfur compounds on coral-associated bacteria. Two coral species, Montipora aequituberculata and Acropora millepora, were sampled and their bacterial communities were characterized by both culture-dependent and molecular techniques. Four genera, Roseobacter, Spongiobacter, Vibrio, and Alteromonas, which were isolated on media with either DMSP or DMS as the sole carbon source, comprised the majority of clones retrieved from coral mucus and tissue 16S rRNA gene clone libraries. Clones affiliated with Roseobacter sp. constituted 28% of the M. aequituberculata tissue libraries, while 59% of the clones from the A. millepora libraries were affiliated with sequences related to the Spongiobacter genus. Vibrio spp. were commonly isolated from DMS and acrylic acid enrichments and were also present in 16S rRNA gene libraries from coral mucus, suggesting that under “normal” environmental conditions, they are a natural component of coral-associated communities. Genes homologous to dddD, and dddL, previously implicated in DMSP degradation, were also characterized from isolated strains, confirming that bacteria associated with corals have the potential to metabolize this sulfur compound when present in coral tissues. Our results demonstrate that DMSP, DMS, and acrylic acid potentially act as nutrient sources for coral-associated bacteria and that these sulfur compounds are likely to play a role in structuring bacterial communities in corals, with important consequences for the health of both corals and coral reef ecosystems.Dimethylsulfoniopropionate (DMSP) is an organic sulfur compound implicated in the formation of clouds via its cleavage product dimethyl sulfide (DMS) and therefore has the potential to exert major cooling effects on climate (9, 38). The production of DMSP is mainly restricted to a few classes of marine macro- and microalgae (27, 68), with the main producers being phytoplankton species belonging to prymnesiophyte and dinoflagellate taxa (28, 62, 67). Recently, significant concentrations of DMSP and DMS have been recorded in association with animals that harbor symbiotic algae such as scleractinian corals and giant clams (7, 8, 68), raising questions about the role of coral reefs in sulfur cycling. The densities of symbiotic dinoflagellates (genus Symbiodinium, commonly known as zooxanthellae) in coral tissues are similar to those recorded for dinoflagellates in phytoplankton blooms (11, 68). Since dinoflagellates are among the most significant producers of DMSP and high intracellular concentrations of DMSP have been found in both cultured zooxanthellae (26) and scleractinian corals (6-8, 25), these observations suggest that endosymbiotic zooxanthellae have an integral role in sulfur cycling in oligotrophic reef waters.Most of the DMSP produced by planktonic dinoflagellates is exuded into the surrounding water, where it is degraded by bacteria via two possible pathways: the first one converts a large fraction (ca. 75%) of dissolved DMSP to methylmercaptopropionate, which is subsequently incorporated into the biomass of microbial cells (22, 27, 66). The second pathway transforms the remaining part of the dissolved DMSP to equimolar concentrations of DMS and acrylic acid (43, 66, 72). This metabolic pathway for DMSP degradation has been identified in the alphaproteobacterial species Sulfitobacter sp. and the enzyme involved (DMSP-dependent DMS lyase [DddL]) characterized (10). Another pathway for DMS formation (without production of acrylate) has been described for Marinomonas sp. and the gene responsible, dddD, identified. In addition, the protein DddR has been directly implicated in the regulation of the gene encoding DddD (66). The DMS produced by these enzymes are then released into the surrounding water (27). Prior to the 1980s, diffusion of supersaturated DMS from the oceans to the atmosphere was thought to be the major removal pathway of this compound from the oceans (35, 72). More recently, however, it has been estimated that between 50 and 80% of the DMS produced by DMSP-degrading bacteria is degraded directly by other types of bacteria (58, 59), although the populations and metabolic pathways involved in the degradation of DMS are still poorly understood.Coral-associated bacterial communities are known to be diverse and highly abundant (12, 30, 48, 49, 52). These dynamic communities exploit a number of habitats associated with corals, including mucus on coral surfaces (48), intracellular niches within coral tissues (3, 16, 45, 47, 52), spaces within coral skeletons (15, 51), and seawater surrounding corals (16, 61). Each of these habitats is believed to harbor different bacterial populations (4, 52). Despite high bacterial diversity, corals have been reported to harbor species-specific microbial communities for beneficial effects; however, their role in coral health is poorly understood (47-50). In coral reef environments, bacteria are dependent upon organic compounds produced by photoautotrophic organisms such as endosymbiotic zooxanthellae (48); therefore, photosynthates translocated to coral tissues and mucus may determine microbial communities closely associated with corals (48, 52). The high levels of DMSP and DMS produced by corals, coupled with the dependence of DMSP and DMS conversion on processes typically involving bacteria, suggest that corals are likely to harbor bacterial species involved in the cycling of these compounds. To investigate the potential of the organosulfur compound DMSP and its breakdown products, DMS and acrylic acid, to drive coral-associated microbial communities, we used these compounds as sole carbon sources to isolate bacteria from two coral species (Montipora aequituberculata and Acropora millepora) and then directly compared these microbial communities with coral-associated microbiota identified using culture-independent analyses. Genes implicated in the metabolism of DMSP were also characterized from isolated strains, confirming that bacteria associated with corals have the potential to metabolize organic sulfur compounds present in coral tissues.     

螺旋藻批式与连续培养及其生长动力学

在内循环气升式光生物反应器中,分别研究了螺旋藻细胞在批式和连续培养条件下的生长特性,结果表明：Richards模型和指数衰减模型可较好地描述批式培养时细胞和碳源底物浓度与培养时间的关系;批式培养时最大细胞生长速率为0371g/d/L,细胞对碳的得率系数为3.439g/gC;连续培养时随着稀释率的增大,细胞和底物浓度分别呈下降和上升趋势;连续培养时最大细胞产率为0.362g/L/d,最佳稀释率为0.45/d,细胞对碳的得率系数为2.050g/gC;所提出的连续培养动力学模型可较好地拟合实验数据。     

高岭土对Fe~(2+)的吸附及其对高岭土中Fe~(3+)生物还原的影响研究

利用异化铁还原微生物可将高岭土中不溶性的Fe3+还原成可溶性的Fe2+,但是此过程中产生的Fe2+能够被高岭土以及异化铁还原微生物吸附,从而影响高岭土中铁的异化还原。本文研究了pH、高岭土量、Fe2+浓度、温度4个因素对高岭土吸附Fe2+的影响;并采用Logistic方程拟合,研究Fe2+及温度对高岭土中Fe3+的生物还原特征。结果表明:pH、高岭土量、浓度、温度4个因素均会影响高岭土吸附Fe2+,当Fe2+吸附在高岭土和微生物菌体表面时,微生物的活性下降,同时高岭土表面Fe3+的生物可利用性也降低,Fe3+生物还原的最大速率减小。     

Application of an M13 bacteriophage displaying tyrosine on the surface for detection of Fe3+ and Fe2+ ions

Ferric and ferrous ion plays critical roles in bioprocesses,their influences in many fields have not been fully explored due to the lack of methods for quantification of ferric and ferrous ions in biological system or complex matrix.In this study,an M13 bacteriophage(phage) was engineered for use as a sensor for ferric and ferrous ions via the display of a tyrosine residue on the P8 coat protein.The interaction between the specific phenol group of tyrosine and Fe~(3+)./ Fe~(2+).was used as the sensor.Transmission electron microscopy showed aggregation of the tyrosine-displaying phages after incubation with Fe~(3+) and Fe~(2+).The aggregated phages infected the host bacterium inefficiently.This phenomenon could be utilized for detection of ferric and ferrous ions.For ferric ions,a calibration curve ranging from 200 nmol/L to 8 μmol/L with a detection limit of 58 nmol/L was acquired.For ferrous ions,a calibration curve ranging from 800 nmol/L to 8μmol/L with a detection limit of 641.7 nmol/L was acquired.The assay was specific for Fe~((3+)) and Fe~((2+)) when tested against Ni~(2+),Pb~(2+),Zn~(2+),Mn~(2+),Co~(2+),Ca~(2+),Cu~(2+),Cr~(3+),Ba~(2+),and K~+.The tyrosine displaying phage to Fe~(3+) and Fe~(2+) interaction would have plenty of room in application to biomatenals and bionanotechnology.     

Studies on the Growth Characteristics and Dynamic Model of Spirulina Under Continuous Culture Conditions

The growth behavior, photosynthetic productivity and carbon utilizing characteristics of filamentous cyanobacterium Spirulina platensis Geitler were investigated in continuous cultures in a 10 L internalloop airlift photobioreactor. It was found that the cell density and the amount of carbon in the reactor increased and decreased with dilution rate respectively, and the relationships among them could well be expressed by the modified Monod equation. When dilution rate was 0.45/d, the rate of cell growth and that of carbon assumption reached their maximum points 0.362 g/(L·d) and 0.177 g/(L·d) respectively. The cell growth yield against carbon was 2.050 g/g. The proposed model of continuous growth fitted the experimental data quite well.     

螺旋藻连续培养与动力学模型

在内循环气升式光生物反应器中 ,研究了钝顶螺旋藻 (SpirulinaplatensisGeitler)细胞的连续生长及其对碳源底物的利用特性。结果表明 :随着稀释率的增大 ,反应器中碳源浓度和细胞浓度分别呈上升和下降趋势 ,它们之间的关系可用Monod类型的方程很好地加以关联。细胞产率和碳消耗速率与稀释率的关系存在峰值现象 :在本实验条件下 ,最大细胞产率为 0 .36 2g/(L·d) ,最大碳消耗速率为 0 .177g/(L·d) ,此时稀释率为 0 .45 /d ,细胞浓度为OD560 =1.2 82 ,细胞对碳的得率系数为 2 .0 5 0g/g。所提出的连续培养动力学模型与实验数据拟合较好     

Role of Nitrosomonas europaea NitABC iron transporter in the uptake of Fe3+-siderophore complexes

Nitrosomonas europaea has a single three-gene operon (nitABC) encoding an iron ABC transporter system (NitABC). Phylogenetic analysis clustered the subunit NitB with Fe³⁺-ABC transporter permease components from other organisms. The N. europaea strain deficient in nitB (nitB::kan) grew well in either Fe-replete or Fe-limited media and in Fe-limited medium containing the catecholate-type siderophore, enterobactin or the citrate-based dihydroxamate-type siderophore, aerobactin. However, the nitB::kan mutant strain was unable to grow in Fe-limited media containing either the hydroxamate-type siderophores, ferrioxamine and ferrichrome or the mixed-chelating type siderophore, pyoverdine. Exposure of N. europaea cells to a ferrichrome analog coupled to the fluorescent moiety naphthalic diimide (Fhu-NI) led to increase in fluorescence in the wild type but not in nitB::kan mutant cells. Spheroplasts prepared from N. europaea wild type exposed to Fhu-NI analog retained the fluorescence, while spheroplasts of the nitB::kan mutant were not fluorescent. NitABC transports intact Fe³⁺-ferrichrome complex into the cytoplasm and is an atypical ABC type iron transporter for Fe³⁺ bound to ferrioxamine, ferrichrome or pyoverdine siderophores into the cytoplasm. The mechanisms to transport iron in either the Fe³⁺ or Fe²⁺ forms or Fe³⁺ associated with enterobactin or aerobactin siderophores into the cell across the cytoplasmic membrane are as yet undetermined.     

Differential Activity of Autochthonous Bacteria in Controlling Drought Stress in Native Lavandula and Salvia Plants Species Under Drought Conditions in Natural Arid Soil

The effectiveness of autochthonous plant growth-promoting rhizobacteria was studied in Lavandula dentata and Salvia officinalis growing in a natural arid Mediterranean soil under drought conditions. These bacteria identified as Bacillus megaterium (Bm), Enterobacter sp. (E), Bacillus thuringiensis (Bt), and Bacillus sp. (Bsp). Each bacteria has different potential to meliorate water limitation and alleviating drought stress in these two plant species. B. thuringiensis promoted growth and drought avoidance in Lavandula by increasing K content, by depressing stomatal conductance, and it controlled shoot proline accumulation. This bacterial effect on increasing drought tolerance was related to the decrease of glutathione reductase (GR) and ascorbate peroxidase (APX) that resulted sensitive indexes of lower cellular oxidative damage involved in the adaptative drought response in B. thuringiensis-inoculated Lavandula plants. In contrast, in Salvia, having intrinsic lower shoot/root ratio, higher stomatal conductance and lower APX and GR activities than Lavandula, the bacterial effects on nutritional, physiological and antioxidant enzymatic systems were lower. The benefit of bacteria depended on intrinsic stress tolerance of plant involved. Lavadula demonstrated a greater benefit than Salvia to control drought stress when inoculated with B. thuringiensis. The bacterial drought tolerance assessed as survival, proline, and indolacetic acid production showed the potential of this bacteria to help plants to grow under drought conditions. B. thuringiensis may be used for Lavandula plant establishment in arid environments. Particular characteristic of the plant species as low shoot/root ratio and high stomatal conductance are important factors controlling the bacterial effectiveness improving nutritional, physiological, and metabolic plant activities.     

Correlation between Possession of a Respiration-Dependent Na+ Pump and Na+ Requirement for Growth of Marine Bacteria

The possession of a respiration-dependent primary sodium pump and the requirement of Na⁺ for growth were investigated in bacterial isolates from marine environments. The bacteria in which NADH oxidase specifically required Na⁺ for maximum activity were believed to possess a primary sodium pump. All bacteria that failed to grow without the addition of NaCl possessed a primary Na⁺ pump. All bacteria that had no primary Na⁺ pump grew without additional NaCl. The primary Na⁺ pump seems to be involved in the Na⁺ requirement of marine bacteria, and this can be regarded as a criterion for the definition of marine bacteria.     

Differential in vitro and in vivo behavior of mouse ascorbate/Fe3+ and diamide oxidized erythrocytes

Chemical oxidation of mouse erythrocytes has been carried out using two different oxidizing systems namely: Diamide and Ascorbate/Fe³⁺ together with different concentrations of the oxidant. These oxidation treatments produced different extents of modification in membrane proteins as was observed by electrophoretic analyses that showed a possible formation of high molecular weight aggregates. Lipid peroxidation was also observed as the result of these chemical treatments. The action of these two oxidation treatments produced different extents of lipid peroxidation in which the effect Ascorbate/Fe³⁺ reached higher values than that shown by diamide treatments. To study the resulting in vitro behavior of such oxidized erythrocytes, we have evaluated the recognition of oxidized erythrocytes by peritoneal macrophages. In the conditions used, diamide oxidized erythrocytes were more highly recognized by macrophages than Ascorbate/Fe³⁺ treated erythrocytes. However, in both cases an influence of serum factors in the recognition process can be inferred. Additionally, we have correlated on one side the action of different oxidation systems on mouse erythrocytes with different in vivo behavior and organ uptake of the oxidized erythrocytes. On the other side, differential targeting of oxidized erythrocytes to a liver or spleen was observed on dependence of the oxidant used.     

Effect of pH and oxalic acid on the reduction of Fe3+ by a biomimetic chelator and on Fe3+ desorption/adsorption onto wood: Implications for brown-rot decay

Fenton reaction is thought to play an important role in wood degradation by brown-rot fungi. In this context, the effect of oxalic acid and pH on iron reduction by a biomimetic fungal chelator and on the adsorption/desorption of iron to/from wood was investigated. The results presented in this work indicate that at pH 2.0 and 4.5 and in the presence of oxalic acid, the phenolate chelator 2,3-dihydroxybenzoic acid (2,3-DHBA) is capable of reducing ferric iron only when the iron is complexed with oxalate to form Fe³⁺-mono-oxalate (Fe(C₂O₄)⁺). Within the pH range tested in this work, this complex formation occurs when the oxalate:Fe³⁺ molar ratio is less than 20 (pH 2.0) or less than 10 (pH 4.5). When aqueous ferric iron was passed through a column packed with milled red spruce (Picea rubens) wood equilibrated at pH 2.0 and 4.5, it was observed that ferric iron binds to wood at pH 4.5 but not at pH 2.0, and the bound iron could then be released by application of oxalic acid at pH 4.5. The release of bound iron was dependent on the amount of oxalic acid applied in the column. When the amount of oxalate was at least 20-fold greater than the amount of iron bound to the wood, all bound iron was released. When Fe–oxalate complexes were applied to the milled wood column equilibrated in the pH range of 2–4.5, iron from Fe–oxalate complexes was bound to the wood only when the pH was 3.6 or higher and the oxalate:Fe³⁺ molar ratio was less than 10. When 2,3-DHBA was evaluated for its ability to release iron bound to the milled wood, it was found that 2,3-DHBA possessed a greater affinity for ferric iron than the wood as 2,3-DHBA was capable of releasing the ferric iron bound to the wood in the pH range 3.6–5.5. These results further the understanding of the mechanisms employed by brown-rot fungi in wood biodegradation processes.     

Investigations on Growth and Metabolism of Plant Cells: VII. Sources of Nitrogen for Tissue Cultures under Optimal Conditions for Their Growth

Tissue cultures from explants of carrot root and potato tuber,stimulated into rapid growth by the addition of coconut milkorAesculus liquid endosperm to the medium, become to a certaindegree heterotrophic for nitrogen. Maximum growth-rates areattained only when nitrate is supplemented with various reducednitrogen compounds. The effects of casein hydrolysate, amino-acidmixtures, ammonia, tryptophan, urea, and allantoin have beeninvestigated, and their possible biochemical roles are discussed.