An Electrical Resistivity Method of Characterizing Hydromechanical and Structural Properties of Compacted Loess During Constant Rate of Strain Compression.

Hydromechanical and structural properties of compacted loess have a significant impact on the stability and reliability of subbase and subgrade, which needs to be quickly determined in the field and laboratory. Hence, an electrical resistivity method was used to characterize the hydromechanical and structural properties of compacted loess during constant rate of strain compression. In the present work, compacted loess samples with a dry density of 1.7 g/cm3, a diameter of 64 mm, a height of 10 mm and different water content ranging from 5-25% were prepared. The constant rate of strain (CRS) tests were conducted by a developed oedometer cell equipped with a pair of horizontal circular electrodes (diameter of 20 mm) and vertical rectangular electrodes (width of 3.5 mm) to determine the electrical resistivity of compacted loess. The results showed that as average water content increases, plastic compression indices increase from 0.220 to 0.350 and the elastic compression indices increase from 0.0152 to 0.030, but they decrease to 0.167 and 0.010 and yield stress decreases from 381.28 kPa to 72.35 kPa. Moreover, as vertical strain increases, the variation trend of average formation factor and average shape factor for the lower water content decreases but increases for the maximum water content, and the anisotropy index first decrease and then tend to increase slightly, which indicates that the structural properties of unsaturated and saturated samples during compression exhibits different trend and the anisotropy of samples tend to be stable as vertical strain increases. As the water content increases, the average formation factor and average shape factor decrease, but the anisotropy index first decreases then increases, suggesting that water content has a significant impact on these electrical indices. More important, The coefficients of average formation factor decrease from 33.830 to -1.698 and the coefficients of average shape factor decrease from 8.339 to -0.398 as water content increases, whereas there is less variation for the coefficient of anisotropic index with a value of 2.190. An equation correlating average formation factor and water content and vertical strain is regressed to characterize the hydromechanical properties of compacted loess by measuring its impedance, which can be used to evaluate the stability of compacted loessic ground and subgrade.

Human LIGIV is synthetically lethal with the loss of Rad54B-dependent recombination and is required for certain chromosome fusion events induced by telomere dysfunction.

Classic non-homologous end joining (C-NHEJ) is the predominant DNA double-strand break repair pathway in humans. Although seven genes Ku70, Ku86, DNA-PK(cs), Artemis, DNA Ligase IV (LIGIV), X-ray cross-complementing group 4 and XRCC4-like factor are required for C-NHEJ, several of them also have ancillary functions. For example, Ku70:Ku86 possesses an essential telomere maintenance activity. In contrast, LIGIV is believed to function exclusively in C-NHEJ. Moreover, a viable LIGIV-null human B-cell line and LIGIV-reduced patient cell lines have been described. Together, these observations suggest that LIGIV (and hence C-NHEJ), albeit important, is nonetheless dispensable, whereas Ku70:Ku86 and telomere maintenance are essential. To confirm this hypothesis, we inactivated LIGIV in the epithelial human cell line, HCT116. The resulting LIGIV-null cell line was viable, verifying that the gene and C-NHEJ are not essential. However, functional inactivation of RAD54B, a key homologous recombination factor, in the LIGIV-null background yielded no viable clones, suggesting that the combined absence of RAD54B/homologous recombination and C-NHEJ is synthetically lethal. Finally, we demonstrate that LIGIV is differentially required for certain chromosome fusion events induced by telomere dysfunction-used for those owing to the overexpression of a dominant negative version of telomere recognition factor 2, but not used for those owing to absence of Ku70:Ku86.

MALDI-TOF mass spectrometry from nucleic acid: development and evaluation of a novel platform for identification of mycobacteria and detection of genetic markers of resistance.

Complete identification methods are critical for evaluating nontuberculous mycobacteria (NTM). Here, we describe a novel diagnostic method for identification of eight NTM, Mycobacterium tuberculosis complex, and three drug resistance markers using PCR/matrix-assisted, laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) from cultured organisms. With this technology, a multiplex end-point PCR is performed for targets of interest. Detection probes that are extended in the presence of a target are added. The extended probes have greater molecular weight and can be detected by MALDI-TOF MS. An AFB Primary Panel was designed to differentiate Mycobacterium avium; Mycobacterium intracellulare subsp. chimaera; Mycobacterium avium complex (other); Mycobacterium abscessus subsp. abscessus, bolletii, and massiliense; Mycobacterium kansasii, and M. tuberculosis complex. This design should cover 90% (3,483/3,691) of mycobacteria seen onsite. A development set of unblinded isolates (n = 217) was used to develop PCR primers, detection probes, and probe barcodes. It demonstrated 99.1% (215/217) agreement with reference methods. An evaluation set using blinded isolates (n = 320) showed an overall sensitivity of 94.3% (range by target: 90.0-100%). Overall specificity from negative media, non-target mycobacteria, and bacteria was 99.1% (108/109; range by target: 94.4-100%). Three drug resistance markers erm (41), rrl, and rrs demonstrated 100%, 91%, and 100% sensitivity, respectively, and >99% specificity. Limit of detection per target ranged from 2.2 × 103 to 9.9 × 106 CFU/mL. The AFB Primary Panel allows for mycobacterial speciation, subspeciation, and resistance mutation detection, which is essential for diagnosis, appropriate therapy, identifying outbreaks, and managing treatment-refractory disease. It can perform with high-throughput and high specificity and sensitivity from isolates.IMPORTANCEEven closely related mycobacteria can have unique treatment patterns, but differentiating these organisms is a challenge. Here, we tested an innovative platform that combines two commonly used technologies and creates something new: matrix-assisted, laser-desorption ionization time-of flight mass spectrometry was performed on PCR amplicons instead of on proteins. This created a robust system with the advantages of PCR (high discriminatory power, high throughput, detection of resistance) with the advantages of mass spectrometry (more targets, lower operational cost) in order to identify closely related mycobacterial organisms.

Ku regulates the non-homologous end joining pathway choice of DNA double-strand break repair in human somatic cells.

The repair of DNA double-strand breaks (DSBs) is critical for the maintenance of genomic integrity and viability for all organisms. Mammals have evolved at least two genetically discrete ways to mediate DNA DSB repair: homologous recombination (HR) and non-homologous end joining (NHEJ). In mammalian cells, most DSBs are preferentially repaired by NHEJ. Recent work has demonstrated that NHEJ consists of at least two sub-pathways-the main Ku heterodimer-dependent or "classic" NHEJ (C-NHEJ) pathway and an "alternative" NHEJ (A-NHEJ) pathway, which usually generates microhomology-mediated signatures at repair junctions. In our study, recombinant adeno-associated virus knockout vectors were utilized to construct a series of isogenic human somatic cell lines deficient in the core C-NHEJ factors (Ku, DNA-PK(cs), XLF, and LIGIV), and the resulting cell lines were characterized for their ability to carry out DNA DSB repair. The absence of DNA-PK(cs), XLF, or LIGIV resulted in cell lines that were profoundly impaired in DNA DSB repair activity. Unexpectedly, Ku86-null cells showed wild-type levels of DNA DSB repair activity that was dominated by microhomology joining events indicative of A-NHEJ. Importantly, A-NHEJ DNA DSB repair activity could also be efficiently de-repressed in LIGIV-null and DNA-PK(cs)-null cells by subsequently reducing the level of Ku70. These studies demonstrate that in human cells C-NHEJ is the major DNA DSB repair pathway and they show that Ku is the critical C-NHEJ factor that regulates DNA NHEJ DSB pathway choice.

Ku86 represses lethal telomere deletion events in human somatic cells.

Nonhomologous end joining (NHEJ), a form of DNA double-strand break (DSB) repair, is conserved from bacteria to humans. One essential NHEJ factor is Ku, which consists of a heterodimer of Ku70 and Ku86. In a plethora of model systems, null mutations for Ku70 or Ku86 present with defects in DNA DSB repair, variable(diversity)joining [V(D)J] recombination, and/or telomere maintenance. The complete loss of Ku from bacteria to mice is, however, compatible with viability. In striking contrast, human patients with mutations of either Ku subunit have never been described. Here, we have used recombinant adeno-associated virus-mediated gene targeting to produce a human somatic cell line that expresses a conditionally null allele of Ku86. The induced loss of Ku86 results in cell death accompanied by massive telomere loss in the form of t-circles. Thus, Ku86 is an essential gene in human somatic cells because of its requirement, not in NHEJ or V(D)J recombination, but in telomere maintenance.

A Reference Range for Plasma Levels of Inorganic Pyrophosphate in Children Using the ATP Sulfurylase Method.

PURPOSE: Generalized arterial calcification of infancy, pseudoxanthoma elasticum, autosomal recessive hypophosphatemic rickets type 2, and hypophosphatasia are rare inherited disorders associated with altered plasma levels of inorganic pyrophosphate (PPi). In this study, we aimed to establish a reference range for plasma PPi in the pediatric population, which would be essential to support its use as a biomarker in children with mineralization disorders. METHODS: Plasma samples were collected from 200 children aged 1 day to 18 years who underwent blood testing for medical conditions not affecting plasma PPi levels. PPi was measured in proband plasma utilizing a validated adenosine triphosphate (ATP) sulfurylase method. RESULTS: The analytical sensitivity of the ATP sulfurylase assay consisted of 0.15 to 10 µM PPi. Inter- and intra-assay coefficients of variability on identical samples were below 10%. The standard range of PPi in the blood plasma of children and adolescents aged 0 to 18 years was calculated as 2.36 to 4.44 µM, with a median of 3.17 µM, with no difference between male and female probands. PPi plasma levels did not differ significantly in different pediatric age groups. MAIN CONCLUSIONS: Our results yielded no noteworthy discrepancy to the reported standard range of plasma PPi in adults (2-5 µM). We propose the described ATP sulfurylase method as a diagnostic tool to measure PPi levels in plasma as a biomarker in the pediatric population.

Seismic Performance of Bridge Piers Constructed with PP-ECC at Potential Plastic Hinge Regions.

This work presents an experimental investigation on the seismic performance of bridge piers constructed with polypropylene fiber reinforced engineered cementitious composite (PP-ECC) at potential plastic hinge regions. Eight solid square bridge piers are tested under a combination of reversed cyclic lateral loading and constant axial vertical loading. The test variables include the reinforcement stirrup ratio (0 vol.%, 0.46 vol.%, and 0.79 vol.%), axial compression ratio (0.1 and 0.3) and height of the PP-ECC regions (0, 250, and 500 mm). Seismic performance of eight specimens is presented and interpreted, including the failure mode, hysteretic curves, loading-resistance capacity, ductility, stiffness degradation, energy dissipation, and equivalent viscous damping ratio. The material test on the PP-ECC plate specimen suggests that the PP-ECC has obvious strain-hardening behavior and multiple fine-cracking characteristics, with the tensile strength and strain capacity greater than 3.2 MPa and 2.6%, respectively. The PP-ECC material applied at the potential plastic hinge regions notably improves the seismic performance and damage tolerance of bridge piers. The influence of the aforementioned crucial parameters has also been investigated in detail. The axial compression ratio and the height of PP-ECC region have a major influence on the seismic performance of PP-ECC piers. In comparison, the stirrup ratio has a limited effect on the seismic behavior of PP-ECC piers. The experimental findings shed light on the mechanism of the PP-ECC that contributes to the seismic performance of bridge piers and provide some valuable guidance in the seismic design of PP-ECC piers.

14-3-3sigma-dependent resistance to cisplatin.

BACKGROUND: A major factor that impedes the clinical success of cisplatin-based chemotherapy for cancer is cisplatin resistance by cancer cells. MATERIALS AND METHODS: The sensitivity of parental HCT116 human colon cancer cell line and its isogenic gene-knockout sub-lines to cisplatin was determined by clonogenicity assay; furthermore, p53 activation, p21 expression, cell cycle arrest and senescence in these cells after cisplatin treatment were investigated. RESULTS: Parental cells were six times more resistant than 14-3-3sigma-knockout (sigma-KO) cells to cisplatin. Moreover, activation of p53, p53-dependent expression of p21 and p21-dependent senescence were observed in sigma-KO, but not parental cells after a treatment with a low cisplatin dose. CONCLUSION: A 14-3-3sigma-dependent mechanism inhibits p53 activation in parental cells treated with a low cisplatin dose, thereby blocking p21 expression that is essential for senescence and consequently conferring to the parental cells a significant degree of resistance to cisplatin.

Analytical validation of a psychiatric pharmacogenomic test.

AIM: The aim of this study was to validate the analytical performance of a combinatorial pharmacogenomics test designed to aid in the appropriate medication selection for neuropsychiatric conditions. MATERIALS & METHODS: Genomic DNA was isolated from buccal swabs. Twelve genes (65 variants/alleles) associated with psychotropic medication metabolism, side effects, and mechanisms of actions were evaluated by bead array, MALDI-TOF mass spectrometry, and/or capillary electrophoresis methods (GeneSight Psychotropic, Assurex Health, Inc.). RESULTS: The combinatorial pharmacogenomics test has a dynamic range of 2.5-20 ng/µl of input genomic DNA, with comparable performance for all assays included in the test. Both the precision and accuracy of the test were >99.9%, with individual gene components between 99.4 and 100%. CONCLUSION: This study demonstrates that the combinatorial pharmacogenomics test is robust and reproducible, making it suitable for clinical use.

Down-regulation of estrogen receptor-alpha in MCF-7 human breast cancer cells after proteasome inhibition.

The eukaryotic proteasome is a 26S ATP-dependent proteolytic complex, which possesses chymotrypsin-like, trypsin-like and peptidyl glutamyl peptide hydrolase (PGPH) activities, which enable the proteasome to degrade all short-lived and many long-lived proteins, and consequently regulate a myriad of activities in cells. In this study, we observed that inhibition of the proteasome, and more specifically, inhibition of the chymotrypsin-like activity of the proteasome, in MCF-7 human breast cancer cells resulted in selective down-regulation of the nuclear estrogen receptor-alpha (ERalpha). Our data indicated that estrogen had no effect, whereas the ERalpha antagonist, tamoxifen, reduced the amount of ERalpha that could be subjected to down-regulation after proteasome inhibition. Furthermore, our data demonstrated that protein synthesis was required for the down-regulation of ERalpha to occur. Collectively, these data indicate the existence of a proteasome-dependent mechanism that is utilized by MCF-7 cells to maintain a steady-state level of ERalpha.

Proteasome-independent down-regulation of estrogen receptor-alpha (ERalpha) in breast cancer cells treated with 4,4'-dihydroxy-trans-stilbene.

Treatment of cells with estrogens and several pure ERalpha antagonists rapidly induces down-regulation of the alpha-type estrogen receptor (ERalpha) in the nucleus by mechanisms that are sensitive to the proteasome inhibitors, MG132 and clasto-lactacystin-beta-lactone. Hence, it is believed that these ER ligands induce down-regulation of ERalpha by proteasome-dependent mechanisms, which serve to control both the amount of transcriptional activity and the level of ligand-bound ERalpha in cells. In this study, we observed that treatment of cultured MCF-7 and T47D human breast cancer cells with the low affinity ER ligand, 4,4'-dihydroxy-trans-stilbene (4,4'-DHS), inhibited the transcriptional activity of ERalpha and induced slow and gradual decrease in the amount of ERalpha protein (henceforth referred to as down-regulation of ERalpha). The 4,4'-DHS-induced down-regulation of ERalpha in MCF-7 cells involved a mechanism that was insensitive to the two most specific proteasome inhibitors, clasto-lactacystin-beta-lactone and epoxomycin, but sensitive to MG132 at concentrations exceeding that required for maximal inhibition of the proteasome in MCF-7 cells. Therefore, 4,4'-DHS appears to induce down-regulation of ERalpha by a proteasome-independent mechanism. Here, we present data to show that both 4-OH and 4'-OH are critical for the ability of 4,4'-DHS to induce down-regulation of ERalpha and suggest that 4,4'-DHS provides a useful scaffold for development of novel ERalpha antagonists.

FADD-dependent apoptosis induction in Jurkat leukemia T-cells by the resveratrol analogue, 3,4,5-trihydroxy-trans-stilbene.

The plant-produced compound, resveratrol (3,5,4'-trihydroxy-trans-stilbene, 3,4,5-THS), induces apoptosis in various human leukemia cell types in vitro, and thus appears to be a promising anti-leukemia agent. In this study, we observed that treatment of resveratrol-resistant Jurkat cells with the resveratrol analogue, 3,4,5-trihydroxy-trans-stilbene (3,4,5-THS), rapidly induced extensive apoptosis, indicating that the apoptotic activity of the analogue differed from that of the parental compound resveratrol. Indeed, we found that treatment of Jurkat cells with 3,4,5-THS, unlike treatment with resveratrol, induced activation of caspase-8 and apoptosis by a Fas-associated death domain (FADD) protein-dependent mechanism without involving the known death ligands CD95 ligand (CD95L), tumor necrosis factor alpha (TNFalpha) and TNF-related apoptosis-inducing ligand (TRAIL). Therefore, 3,4,5-THS induced activation of a FADD-dependent apoptotic mechanism that was unresponsive to the parental compound resveratrol. Therefore, the ability of 3,4,5-THS, but not resveratrol, to induce apoptosis demonstrates a structure-associated apoptotic activity of the resveratrol analogue.

A unique approach for high level expression and production of a recombinant cobra neurotoxin in Escherichia coli.

In this report, we describe a simple approach to produce a large quantity of a recombinant cobra neurotoxin containing four pairs of disulfide bonds. A cDNA encoding the toxin was fused, in frame, to the carboxyl termini of thioredoxin via a linker sequence encoding two amino acids, Asp and Pro. Due to the presence of thioredoxin, a soluble form of the fusion protein was expressed in a compartment, sensitive to osmotic pressure, in Escherichia coli. The fusion protein was released into the solution with low ionic strength under an osmotic shock treatment, and purified in a single step using an ion exchange chromatography column. The purified protein was treated in diluted hydrochloric acid to induce hydrolysis of the protein at the Asp-Pro linker site. Then, the recombinant neurotoxin was purified by gel filtration of the acid-treated sample. When the biological activity of the purified toxin was assayed, it was as potent as the natural toxin. Using this protocol, approximately 12 mg of pure recombinant neurotoxin can be produced from one liter of bacterial culture. More importantly, this protocol can be easily used for the production of the toxin at a larger scale with low cost. The approach outlined in this report will be suitable for the production of other recombinant proteins especially those of the 'three-finger' family.

Camptothecin and 9-nitrocamptothecin (9NC) as anti-cancer, anti-HIV and cell-differentiation agents. Development of resistance, enhancement of 9NC-induced activities and combination treatments in cell and animal models.

The anticancer drug, 9-nitrocamptothecin (9NC), has demonstrated an unprecedented activity against human caner cells grown in cultures and as xenografts in nude mice. 9NC-induced apoptosis of cancer cells is mediated by the nuclear enzyme, topoisomerase I, and executed by pathways that involve cytochrome c release from the mitochondrion and/or activation of death receptors depending on the cell type. Alternatively, 9NC has exhibited ability to induce differentiation or senescence of certain cell types in vitro. In several instances, the 9NC activities can be regulated by Bcl-2 family proteins and cell cycle-associated proteins, p53, p21 and Cdks. Also, 9NC can inhibit HIV replication in infected T- and monocytic cells in vitro. Development of resistance to 9NC, associated with mutations in the topoisomerase I gene, can be overcome by regulating specific proteins, such as RKIP, other than topoisomerase I. Finally, derivatives (i.e., alkyl esters) of 9NC, liposome-encapsulated 9NC and combined treatment of 9NC with ionizing radiation or hyperthermia are other approaches to enhance the apoptotic activity of 9NC against human cancer cells.

DNA ligase III and DNA ligase IV carry out genetically distinct forms of end joining in human somatic cells.

Ku-dependent C-NHEJ (classic non-homologous end joining) is the primary DNA EJing (end joining) repair pathway in mammals. Recently, an additional EJing repair pathway (A-NHEJ; alternative-NHEJ) has been described. Currently, the mechanism of A-NHEJ is obscure although a dependency on LIGIII (DNA ligase III) is often implicated. To test the requirement for LIGIII in A-NHEJ we constructed a LIGIII conditionally-null human cell line using gene targeting. Nuclear EJing activity appeared unaffected by a deficiency in LIGIII as, surprisingly, so were random gene targeting integration events. In contrast, LIGIII was required for mitochondrial function and this defined the gene's essential activity. Human Ku:LIGIII and Ku:LIGIV (DNA ligase IV) double knockout cell lines, however, demonstrated that LIGIII is required for the enhanced A-NHEJ activity that is observed in Ku-deficient cells. Most unexpectedly, however, the majority of EJing events remained LIGIV-dependent. In conclusion, although human LIGIII has an essential function in mitochondrial maintenance, it is dispensable for most types of nuclear DSB repair, except for the A-NHEJ events that are normally suppressed by Ku. Moreover, we describe that a robust Ku-independent, LIGIV-dependent repair pathway exists in human somatic cells.

A role for XLF in DNA repair and recombination in human somatic cells.

Classic non-homologous end-joining (C-NHEJ) is required for the repair of radiation-induced DNA double-strand breaks (DSBs) in mammalian cells and plays a critical role in lymphoid V(D)J recombination. A core C-NHEJ component is the DNA ligase IV co-factor, Cernunnos/XLF (hereafter XLF). In patients, mutations in XLF cause predicted increases in radiosensitivity and deficits in immune function, but also cause other less well-understood pathologies including neural disorders. To characterize XLF function(s) in a defined genetic system, we used a recombinant adeno-associated virus-mediated gene targeting strategy to inactivate both copies of the XLF locus in the human HCT116 cell line. Analyses of XLF-null cells (which were viable) showed that they were highly sensitive to ionizing radiation and a radiomimetic DNA damaging agent, etoposide. XLF-null cells had profound DNA DSB repair defects as measured by in vivo plasmid end-joining assays and were also dramatically impaired in their ability to form either V(D)J coding or signal joints on extrachromosomal substrates. Thus, our somatic XLF-null cell line recapitulates many of the phenotypes expected from XLF patient cell lines. Subsequent structure:function experiments utilizing the expression of wild-type and mutant XLF cDNAs demonstrated that all of the phenotypes of an XLF deficiency could be rescued by the overexpression of a wild-type XLF cDNA. Unexpectedly, mutant forms of XLF bearing point mutations at amino acid positions L115 and L179, also completely complemented the null phenotype suggesting, in contrast to predictions to the contrary, that these mutations do not abrogate XLF function. Finally, we demonstrate that the absence of XLF causes a small, but significant, increase in homologous recombination, implicating XLF in DSB pathway choice regulation. We conclude that human XLF is a non-essential, but critical, C-NHEJ-repair factor.

Submicroscopic deletion of 5q involving tumor suppressor genes (CTNNA1, HSPA9) and copy neutral loss of heterozygosity associated with TET2 and EZH2 mutations in a case of MDS with normal chromosome and FISH results.

Advances in genome-wide molecular cytogenetics allow identification of novel submicroscopic DNA copy number alterations (aCNAs) and copy-neutral loss of heterozygosity (cnLOH) resulting in homozygosity for known gene mutations in myeloid neoplasms. We describe the use of an oligo-SNP array for genomic profiling of aCNA and cnLOH, together with sequence analysis of recurrently mutated genes, in a patient with myelodysplastic syndrome (MDS) presenting with normal karyotype and FISH results. Oligo-SNP array analysis revealed a hemizygous deletion of 896 kb at chromosome 5q31.2, representing the smallest 5q deletion reported to date. The deletion involved multiple genes, including two tumor suppressor candidate genes (CTNNA1 and HSPA9) that are associated with MDS/AML. The SNP-array study also detected 3 segments of somatic cnLOH: one involved the entire long arm of chromosome 4; the second involved the distal half of the long arm of chromosome 7, and the third encompassed the entire chromosome 22 (UPD 22). Sequence analysis revealed mutations in TET2 (4q), EZH2 (7q), ASXL1 (20q11.21), and RUNX1 (21q22.3). Coincidently, TET2 and EZH2 were located at segments of cnLOH resulting in their homozygosity. Loss of heterozygosity affecting these two chromosomes and mutations in TET2 and EZH2 are indicative of a myelodysplastic syndrome with a poor prognosis. Deletion of the tumor suppressor genes CTNNA1 and HSPA9 is also likely to contribute to a poor prognosis. Furthermore, the original cnLOHs in multiple chromosomes and additional cnLOH 14q in the follow-up study suggest genetic evolution of the disease and poor prognosis. This study attests to the fact that some patients with a myelodysplastic syndrome who exhibit a normal karyotype may have underlying genetic abnormalities detectable by chromosomal microarray and/or targeted mutation analyses.

Identification of a TRAP transporter for malonate transport and its expression regulated by GtrA from Sinorhizobium meliloti.

Sinorhizobium meliloti can live as a saprophyte in soil or as a nitrogen-fixing symbiont inside the root nodule cells of alfalfa and related legumes by utilizing different organic compounds as its carbon source. Here we have identified the matPQMAB operon in S. meliloti 1021. Within this operon, matP, matQ and the M region of the fused gene matMA encode an extracytoplasmic solute receptor, a small transmembrane protein and a large transmembrane protein, consisting of three components of the tripartite ATP-independent periplasmic (TRAP) transporter for malonate transport. The A region of the fused gene matMA and matB encode malonate-metabolizing enzymes, malonyl-CoA decarboxylase and malonyl-CoA synthetase. The null mutant of each matPQMAB gene is unable to grow on M9 minimal medium containing malonate as the sole carbon source. However, these mutants can induce the formation of efficient nitrogen-fixing root nodules on alfalfa. The matPQMAB operon is expressed in free-living bacterial cells and symbiotic bacterial cells from infection threads and root nodules. The GntR family transcriptional regulator, GtrA, specifically binds the promoter of the matPQMAB operon, positively regulating its expression. Moreover, the matPQMAB can be transcriptionally induced by malonate. These results suggested that a C(3)-dicarboxylic acid TRAP transporter is responsible for malonate transport in S. meliloti.

[Comprehensive evaluation of cultivated black soil fertility].

Black soil is one of the main soil types in northeastern China, and is a valuable soil resource of this country. Based on the analysis of the physical and chemical properties of soil samples collected from the north-south transaction of black soil, the index system of black soil fertility was established, the fertility level was evaluated and classified by Fuzzy and Factor Analysis, and the fertility map of black soil zone was drawn with GIS software ArcInfo. It was found that the humus layer in black soil region was thick in north and thin in south, which was due to the climatic condition and soil-forming process. The soil fertility level was high in east and low in west. From north to south, it was decreased in the order of central part > northern part > south part. In most part of this region, soil fertility level was medium, and the area accounted for 73.6% of the black soil area.