Trees,Mycorrhiza and Minerals –Field Relevance of in vitro Experiments

Ectomycorrhizal fungi are mutualistic symbionts of boreal forest trees and may mediate mineral weathering through their direct access to photosyntentically derived carbon. In soil, fungal mycelia (i) provide a large surface for nutrient uptake; (ii) induce intense colonization of nutrient rich substrates; (iii) cause local acidification and (iv) produce organic acids. Mechanisms of ectomyorrhizal fungi induced weathering in response to nutrient limiting growth conditions remains largely unresolved. This review summarizes how current knowledge on fungal weathering is affected by experimental setup and conditions, i.e., pure or symbiotic growth, nitrogen source, the mean of detecting weathering activity and species examined.     

Pseudomonas azotoformans F77和Pseudomonas paracarnis P1风化黑云母的效应及机制比较

【目的】比较高效矿物风化固氮假单胞菌(Pseudomonas azotoformans) F77及其亲缘关系较近的假单胞菌(Pseudomonas paracarnis) P1风化黑云母的效应和机制。【方法】通过检测两株菌在不同时间点的发酵液中细胞数量、pH值、葡萄糖剩余量、葡萄糖酸浓度和可溶性Fe、Al释放量,比较它们对黑云母的风化效果与生理机制。采用RNA-seq技术研究这两株菌风化黑云母过程中出现差异的分子机制。【结果】在持续5 d的风化试验中,菌株F77发酵液中的细胞数量和pH值低于菌株P1,葡萄糖酸浓度是菌株P1的27.3-53.9倍,Fe和Al元素的释放量是菌株P1的3.3-23.3倍。比较转录组数据表明,菌株F77特有的基因数量(2 872)和差异基因数量(1 832)均多于菌株P1 (分别为1 903和1 258)。菌株F77在胞内物质跨膜转运与碳代谢、细胞运动、趋化与信号诱导等途径中基因数量也高于菌株P1。此外,菌株F77的超氧化物歧化酶和过氧化氢酶基因差异表达倍数、葡萄糖酸合成基因数量和差异表达倍数也明显高于菌株P1。【结论】菌株F77风化黑云母以及合成葡萄糖酸的能力显著高于菌株P1。菌株F77通过产生葡萄糖酸来促进黑云母的风化。添加黑云母显著促进了菌株F77胞内与矿物风化相关基因的表达,如物质跨膜转运、细胞运动与趋化、信号诱导、碳代谢及能量代谢等途径基因。此外,葡萄糖酸合成途径基因、超氧化物歧化酶基因以及过氧化氢酶基因在矿物风化中可能发挥重要作用。     

Root-associated bacteria contribute to mineral weathering and to mineral nutrition in trees: a budgeting analysis

The principal nutrient source for forest trees derives from the weathering of soil minerals which results from water circulation and from plant and microbial activity. The main objectives of this work were to quantify the respective effects of plant- and root-associated bacteria on mineral weathering and their consequences on tree seedling growth and nutrition. That is why we carried out two column experiments with a quartz-biotite substrate. The columns were planted with or without pine seedlings and inoculated or not with three ectomycorrhizosphere bacterial strains to quantify biotite weathering and pine growth and to determine how bacteria improve pine growth. We showed that the pine roots significantly increased biotite weathering by a factor of 1.3 for magnesium and 1.7 for potassium. We also demonstrated that the inoculation of Burkholderia glathei PML1(12) significantly increased biotite weathering by a factor of 1.4 for magnesium and 1.5 for potassium in comparison with the pine alone. In addition, we observed a significant positive effect of B. glathei PMB1(7) and PML1(12) on pine growth and on root morphology (number of lateral roots and root hairs). We demonstrated that PML1(12) improved pine growth when the seedlings were supplied with a nutrient solution which did not contain the nutrients present in the biotite. No improvement of pine growth was observed when the seedlings were supplied with all the nutrients necessary for pine growth. We therefore propose that the growth-promoting effect of B. glathei PML1(12) mainly resulted from the improved plant nutrition via increased mineral weathering.     

To be or not to be planktonic? Self‐inhibition of biofilm development

The transition between planktonic growth and biofilm formation represents a tightly regulated developmental shift that has substantial impact on cell fate. Here, we highlight different mechanisms through which bacteria limit their own biofilm development. The mechanisms involved in these self‐inhibition processes include: (i) regulation by secreted small molecules, which govern intricate signalling cascades that eventually decrease biofilm development, (ii) extracellular polysaccharides capable of modifying the physicochemical properties of the substratum and (iii) extracellular DNA that masks an adhesive structure. These mechanisms, which rely on substances produced by the bacterium and released into the extracellular milieu, suggest regulation at the communal level. In addition, we provide specific examples of environmental cues (e.g. blue light or glucose level) that trigger a cellular response reducing biofilm development. All together, we describe a diverse array of mechanisms underlying self‐inhibition of biofilm development in different bacteria and discuss possible advantages of these processes.     

Root-Associated Bacteria Contribute to Mineral Weathering and to Mineral Nutrition in Trees: a Budgeting Analysis

The principal nutrient source for forest trees derives from the weathering of soil minerals which results from water circulation and from plant and microbial activity. The main objectives of this work were to quantify the respective effects of plant- and root-associated bacteria on mineral weathering and their consequences on tree seedling growth and nutrition. That is why we carried out two column experiments with a quartz-biotite substrate. The columns were planted with or without pine seedlings and inoculated or not with three ectomycorrhizosphere bacterial strains to quantify biotite weathering and pine growth and to determine how bacteria improve pine growth. We showed that the pine roots significantly increased biotite weathering by a factor of 1.3 for magnesium and 1.7 for potassium. We also demonstrated that the inoculation of Burkholderia glathei PML1(12) significantly increased biotite weathering by a factor of 1.4 for magnesium and 1.5 for potassium in comparison with the pine alone. In addition, we observed a significant positive effect of B. glathei PMB1(7) and PML1(12) on pine growth and on root morphology (number of lateral roots and root hairs). We demonstrated that PML1(12) improved pine growth when the seedlings were supplied with a nutrient solution which did not contain the nutrients present in the biotite. No improvement of pine growth was observed when the seedlings were supplied with all the nutrients necessary for pine growth. We therefore propose that the growth-promoting effect of B. glathei PML1(12) mainly resulted from the improved plant nutrition via increased mineral weathering.     

Airborne Bacteria in the Atmospheric Surface Layer: Temporal Distribution above a Grass Seed Field

Temporal airborne bacterial concentrations and meteorological conditions were measured above a grass seed field in the Willamette River Valley, near Corvallis, Oreg., in the summer of 1993. The concentration of airborne bacteria had a maximum of 1,368.5 CFU/m(sup3), with a coefficient of variation of 90.5% and a mean of 121.3 CFU/m(sup3). The lowest concentration of bacteria occurred during the predawn hours, with an average of 32.2 CFU/m(sup3), while sunrise and early evening hours had the highest averages (164.7 and 158.1 CFU/m(sup3), respectively). The concentrations of bacteria in the atmosphere varied greatly, with a maximum difference between two 2-min samples of 1,995 CFU/m(sup3). The concentrations of bacteria in the atmosphere could be divided into five time periods during the day that were thought to be related to the local diurnal sea breeze and Pacific Coast monsoon weather conditions as follows: (i) the nighttime minimum concentration, i.e., 2300 to 0600 h; (ii) the sunrise peak concentration, i.e., 0600 to 0800 h; (iii) the midday accumulating concentration, i.e., 0800 to 1515 h; (iv) the late-afternoon sea breeze trough concentration, i.e., 1515 to 1700 h; and (v) the evening decrease to the nighttime minimum concentration, i.e., 1700 to 2300 h. The sunrise peak concentration (period ii) is thought to be a relatively general phenomenon dependent on ground heating by the sun, while the afternoon trough concentration is thought to be a relatively local phenomenon dependent on the afternoon sea breeze. Meteorological conditions are thought to be an important regulating influence on airborne bacterial concentrations in the outdoor atmosphere in the Willamette River Valley.     

Membrane permeability modifications are involved in antibiotic resistance in Klebsiella pneumoniae

Two Klebsiella pneumoniae strains selected according to their high cross-resistance pattern to cephalosporins were characterized by (i) outer membrane protein content such as OmpA or nonspecific porins, (ii) MICs of various cephalosporins and unrelated antibiotics, (iii) beta-lactamase production, and (iv) active efflux of fluoroquinolones. An association of porin deficiency and beta-lactamase production induced a noticeable cephalosporin resistance. In addition to these mechanisms, the presence of an active efflux participating in high-level fluoroquinolone resistance was identified in one strain. The decrease of antibiotic uptake associated with efflux explains the Klebsiella adaptation against the drugs present in the environment.     

Improved Procedure for Identification of Group D Enterococci with Two New Media

The aerosol survival in air was determined for Pasteurella tularensis live vaccine strain (LVS) as a function of relative humidity (RH). Three different preparations of bacteria were used: (i) liquid suspension of P. tularensis LVS in spent culture medium; (ii) powders of P. tularensis LVS freeze-dried in spent culture fluid; (iii) P. tularensis LVS freeze-dried in spent culture fluid and then reconstituted with distilled water and disseminated as a liquid suspension. Preparation (i) gave greatest survival at high RH and lowest survival at intermediate RH. Preparation (ii), in contrast, gave greatest survival at low RH and minimum survival at 81% RH. Preparation (iii) was the same as preparation (i), i.e., the process of freeze-drying and reconstituting with distilled water before aerosol formation had little or no effect upon aerosol survival as a function of RH. Hence, control of aerosol survival appears to be through the water content of P. tularensis LVS at the moment of aerosol generation rather than the water content of the bacteria in the aerosol phase.     

Aerosol Survival of Pasteurella tularensis and the Influence of Relative Humidity

The aerosol survival in air was determined for Pasteurella tularensis live vaccine strain (LVS) as a function of relative humidity (RH). Three different preparations of bacteria were used: (i) liquid suspension of P. tularensis LVS in spent culture medium; (ii) powders of P. tularensis LVS freeze-dried in spent culture fluid; (iii) P. tularensis LVS freeze-dried in spent culture fluid and then reconstituted with distilled water and disseminated as a liquid suspension. Preparation (i) gave greatest survival at high RH and lowest survival at intermediate RH. Preparation (ii), in contrast, gave greatest survival at low RH and minimum survival at 81% RH. Preparation (iii) was the same as preparation (i), i.e., the process of freeze-drying and reconstituting with distilled water before aerosol formation had little or no effect upon aerosol survival as a function of RH. Hence, control of aerosol survival appears to be through the water content of P. tularensis LVS at the moment of aerosol generation rather than the water content of the bacteria in the aerosol phase.     

Detection and organization of atrazine-degrading genetic potential of seventeen bacterial isolates belonging to divergent taxa indicate a recent common origin of their catabolic functions

A collection of 17 atrazine-degrading bacteria isolated from soils was studied to determine the composition of the atrazine-degrading genetic potential (i.e. trzN, trzD and atz) and the presence of IS1071. The characterization of seven new atrazine-degrading bacteria revealed for the first time the trzN-atzBC gene composition in Gram-negative bacteria such as Sinorhizobium sp. or Polaromonas sp. Three main atrazine-degrading gene combinations (i) trzN-atzBC, (ii) atzABC-trzD and (iii) atzABCDEF were observed. The atz and trz genes were often located on plasmids, suggesting that plasmid conjugation could play an important role in their dispersion. In addition, the observation of these genes (i) on the chromosome, (ii) on the same DNA fragment but on different plasmids and (iii) on DNA fragments also hybridizing with IS1071 suggests that transposition may also contribute to disperse the atrazine-degrading genes.     

Overexpression of promyelocytic leukemia protein precludes the dispersal of ND10 structures and has no effect on accumulation of infectious herpes simplex virus 1 or its proteins

A key early event in the replication of herpes simplex virus 1 (HSV-1) is the localization of infected-cell protein no. 0 (ICP0) in nuclear structures knows as ND10 or promyelocytic leukemia oncogenic domains (PODs). This is followed by dispersal of ND10 constituents such as the promyelocytic leukemia protein (PML), CREB-binding protein (CBP), and Daxx. Numerous experiments have shown that this dispersal is mediated by ICP0. PML is thought to be the organizing structural component of ND10. To determine whether the virus targets PML because it is inimical to viral replication, telomerase-immortalized human foreskin fibroblasts and HEp-2 cells were transduced with wild-type baculovirus or a baculovirus expressing the M(r) 69,000 form of PML. The transduced cultures were examined for expression and localization of PML in mock-infected and HSV-1-infected cells. The results obtained from studies of cells overexpressing PML were as follows. (i) Transduced cells accumulate large amounts of unmodified and SUMO-I-modified PML. (ii) Mock-infected cells exhibited enlarged ND10 structures containing CBP and Daxx in addition to PML. (iii) In infected cells, ICP0 colocalized with PML in ND10 early in infection, but the two proteins did not overlap or were juxtaposed in orderly structures. (iv) The enlarged ND10 structures remained intact at least until 12 h after infection and retained CBP and Daxx in addition to PML. (v) Overexpression of PML had no effect on the accumulation of viral proteins representative of alpha, beta, or gamma groups and had no effect on the accumulation of infectious virus in cells infected with wild-type virus or a mutant (R7910) from which the alpha 0 genes had been deleted. These results indicate the following: (i) PML overexpressed in transduced cells cannot be differentiated from endogenous PML with respect to sumoylation and localization in ND10 structures. (ii) PML does not affect viral replication or the changes in the localization of ICP0 through infection. (iii) Disaggregation of ND10 structures is not an obligatory event essential for viral replication.     

The mineral weathering ability of Collimonas pratensis PMB3(1) involves a Malleobactin-mediated iron acquisition system

Mineral weathering by microorganisms is considered to occur through a succession of mechanisms based on acidification and chelation. While the role of acidification is established, the role of siderophores is difficult to disentangle from the effect of the acidification. We took advantage of the ability of strain Collimonas pratensis PMB3(1) to weather minerals but not to acidify depending on the carbon source to address the role of siderophores in mineral weathering. We identified a single non-ribosomal peptide synthetase (NRPS) responsible for siderophore biosynthesis in the PMB3(1) genome. By combining iron-chelating assays, targeted mutagenesis and chemical analyses (HPLC and LC-ESI-HRMS), we identified the siderophore produced as malleobactin X and how its production depends on the concentration of available iron. Comparison with the genome sequences of other collimonads evidenced that malleobactin production seems to be a relatively conserved functional trait, though some collimonads harboured other siderophore synthesis systems. We also revealed by comparing the wild-type strain and its mutant impaired in the production of malleobactin that the ability to produce this siderophore is essential to allow the dissolution of hematite under non-acidifying conditions. This study represents the first characterization of the siderophore produced by collimonads and its role in mineral weathering.     

Putrescine stimulates chemiosmotic ATP synthesis

Putrescine is a main polyamine found in animals, plants and microbes, but the molecular mechanism underlying its mode of action is still obscure. In vivo chlorophyll a fluorescence in tobacco leaf discs indicated that putrescine treatment affects the energization of the thylakoid membrane. Molecular dissection of the electron transport chain by biophysical and biochemical means provided new evidence that putrescine can play an important bioenergetic role acting as a cation and as a permeant natural buffer. We demonstrate that putrescine increases chemiosmotic ATP synthesis more than 70%. Also a regulation of the energy outcome by small changes in putrescine pool under the same photonic environment (i.e., photosynthetically active radiation) is shown. The proposed molecular mechanism has at least four conserved features: (i) presence of a membrane barrier, (ii) a proton-driven ATPase, (iii) a DeltapH and (iv) a pool of putrescine.     

Chondrocyte aggregation in suspension culture is GFOGER-GPP- and beta1 integrin-dependent

Isolated chondrocytes form aggregates in suspension culture that maintain chondrocyte phenotype in a physiological pericellular environment. The molecular mechanisms involved in chondrocyte aggregation have not been previously identified. Using this novel suspension culture system, we performed mRNA and protein expression analysis along with immunohistochemistry for potential cell adhesion molecules and extracellular matrix integrin ligands. Inhibition of aggregation assays were performed using specific blocking agents. We found that: (i) direct cell-cell interactions were not involved in chondrocyte aggregation, (ii) chondrocytes in aggregates were surrounded by a matrix rich in collagen II and cartilage oligomeric protein (COMP), (iii) aggregation depends on a beta1-integrin, which binds a triple helical GFOGER sequence found in collagens, (iv) integrin alpha10-subunit is the most highly expressed alpha-subunit among those tested, including alpha5, in aggregating chondrocytes. Taken together, this body of evidence suggests that the main molecular interaction involved in aggregation of phenotypically stable chondrocytes is the alpha10beta1-collagen II interaction.     

Fungal degradation of calcium-, lead- and silicon-bearing minerals

The aim of this study was to examine nutritional influence on the ability of selected filamentous fungi to mediate biogenic weathering of the minerals, apatite, galena and obsidian in order to provide further understanding of the roles of fungi as biogeochemical agents, particularly in relation to the cycling of metals and associated elements found in minerals. The impact of three organic acid producing fungi (Aspergillus niger, Serpula himantioides and Trametes versicolor) on apatite, galena and obsidian was examined in the absence and presence of a carbon and energy source (glucose). Manifestation of fungal weathering included corrosion of mineral surfaces, modification of the mineral substrate through transformation into secondary minerals (i.e. crystal formation) and hyphal penetration of the mineral substrate. Physicochemical interactions of fungal metabolites, e.g. H⁺ and organic acids, with the minerals are thought to be the primary driving forces responsible. All experimental fungi were capable of mineral surface colonization in the absence and presence of glucose but corrosion of the mineral surface and secondary mineral formation were affected by glucose availability. Only S. himantioides and T. versicolor were able to corrode apatite in the absence of glucose but none of the fungi were capable of doing so with the other minerals. In addition, crystal formation with galena was entirely dependent on the availability of glucose. Penetration of the mineral substrates by fungal hyphae occurred but this did not follow any particular pattern. Although the presence of glucose in the media appeared to influence positively the mineral penetrating abilities of the fungi, the results obtained also showed that some geochemical change(s) might occur under nutrient-limited conditions. It was, however, unclear whether the hyphae actively penetrated the minerals or were growing into pre-existing pores or cracks.     

Mineral and carbon usage of two synthetic pyrethroid degrading bacterial isolates

AIMS: To investigate the biodegrading ability and cometabolism of synthetic pyrethroid (SP) utilizing bacteria in cultures with various minerals and carbon sources. METHODS AND RESULTS: Previously isolated SP-degrading Pseudomonas sp. and Serratia sp. were used in cultures containing either flumethrin SP or cypermethrin SP formulations. The culture media consisted of either (i) water only, (ii) water and sucrose, (iii) mineral broth or (iv) mineral broth and sucrose. The growth of both organisms was greatest in the mineral broth and sucrose medium, but the growth-limiting factor for Pseudomonas sp. strain Circle was the mineral content whereas for Serratia sp. strain White it was the carbon substrate. CONCLUSION: The greatest extent of degradation of both SP-based compounds occurred with Pseudomonas sp. strain Circle but was dependant on the medium. SIGNIFICANCE AND IMPACT OF THE STUDY: This investigation could lead to the development of a relatively inexpensive medium supplement to enhance the microbial biodegradation of undesirable compounds, either in situ or ex situ. In this particular case, for the biodegradation of SPs used in sheep dip.     

Effects of Na+ on the Predominant K+ Channel in the Tonoplast of Chara: Decrease of Conductance by Blocks in 100 Nanosecond Range and Induction of Oligo- or Poly-subconductance Gating Modes

We present three mechanisms by which Na⁺ inhibits the open channel currents of the predominant K⁺ channel in the tonoplast of Chara corallina: (i) Fast block, i.e., short (100 ns range) interruptions of the open channel current which are determined by open channel noise analysis, (ii): Oligo-subconductance mode, i.e., a gating mode which occurs preferentially in the presence of Na⁺; this mode comprises a discrete number (here 3) of open states with smaller conductances than normal, and (iii): Polysubconductance mode, i.e., a gating mode with a nondiscrete, large number (>30) of states with smaller conductances than the main open channel conductance. This novel mode has also been observed only in the presence of Na⁺. Received: 16 November 1999/Revised: 8 February 2000