Sinorhizobium meliloti nifA is important in fixing nitrogen during symbiosis. A nifA null mutant induces small white invalid nodules in the roots of host plant. The additional phenotypic alterations associated with th...Sinorhizobium meliloti nifA is important in fixing nitrogen during symbiosis. A nifA null mutant induces small white invalid nodules in the roots of host plant. The additional phenotypic alterations associated with the disruption of the nifA gene are reported in this study. Under a free-living state, S. meliloti nifA mutant reduces its ability to swarm on a half-solid plate. Interestingly, the AHL （Acylhomoserine lactones） contents in the nifA mutant are lower than that of the wild type during the lag phase, whereas it is reversed in the logarithmic and stationary phases. Quantitative spectrophotometric assays reveal that the total amount of extracellular proteins of the nifA mutant are lower than that of the wild type. In addition, the mutant abolishes its nodulation competitive ability during symbiosis. These findings indicate that NifA plays a regulatory role in multiple cellular processes in S. meliloti.展开更多
Seventeen Sinorhizobium meliloti strains from seven provinces in China were used to screen highly effective strains for alfalfa cultivar in a greenhouse study and their symbiotic relationship and competitive ability w...Seventeen Sinorhizobium meliloti strains from seven provinces in China were used to screen highly effective strains for alfalfa cultivar in a greenhouse study and their symbiotic relationship and competitive ability were studied in the field. CCBAU30138 was the most effective strain, as evidenced by increase in dry weights. A field experiment showed that the inoculation of alfalfa with CCBAU30138 resulted in increases of 11.9% and 19.6% of dry matter production and crude protein production, respectively, in forage of monocultured plants. The total dry matter yields of alfalfa and tall fescue in binary culture were increased by 16.3% by inoculation of alfalfa with this strain. These results showed that S. rneliloti strain CCBAU30138 was an effective inoculant both in the greenhouse and in the field. The analysis of randomly amplified polymorphic DNA （RAPD） by polymerase chain reaction （PCR） from nodule extracts showed that the strain CCBAU30138 had high competitiveness in the field. It occupied 47.5% of nodules in alfalfa monoculture and 44.4% of nodules in alfalfa-tall fescue binary culture after 20 weeks of growth. In conclusion, a simple system to select highly effective and competitive symbiotic strains specific to alfalfa was established. Using this system, a s.train suitable for the alfalfa cultivar ‘Vector＇ grown in Wuqiao County of Hebei Province was obtained.展开更多
Alfalfa （Medicago sativa L.） is being grown in harsh environment in Iraq and is mostly subjected to abiotic stresses such as drought, salinity, pH and temperature. Both alfalfa and its nitrogen fixing symbiotic bact...Alfalfa （Medicago sativa L.） is being grown in harsh environment in Iraq and is mostly subjected to abiotic stresses such as drought, salinity, pH and temperature. Both alfalfa and its nitrogen fixing symbiotic bacteria Sinorhizobium meliloti are affected by these environmental stresses. Enhancing nitrogen fixation biologically could be achieved through selection of tolerant strains of S. meliloti to these environmental stresses and inoculating them to the crop, also growing tolerant cultivars. This study examines phenotypic diversity for tolerance to drought, salinity, temperature and pH. Sixty isolates sampled from different areas of Iraq. The results revealed high degree of phenotypic diversity in Sinorhizobium populations. Furthermore, the isolates which showed tolerance to drought stress also showed tolerance to salinity and high degree of temperature, indicating direct relationship between three physiological path ways. Also 58.3% of drought tolerant isolates were alkaline tolerant they tolerated up to pH 9, point to say almost all drought tolerant isolates in this study illustrated strong ＋ positive reaction to catalase enzyme. And 91.6% themes were negative for Gelatinase enzyme test. While only 50% of drought sensitive isolates were negative for drought sensitive isolates could grow at high temperature （42 ℃）.展开更多
Soil bacteria Sinorhizobium meliloti had enormous agricultural value, due to their ability in fixing nitrogen symbiotically with an important forage crop legume--alfalfa. The aims of the present study were （1） to is...Soil bacteria Sinorhizobium meliloti had enormous agricultural value, due to their ability in fixing nitrogen symbiotically with an important forage crop legume--alfalfa. The aims of the present study were （1） to isolate indigenous S. meliloti from different field sites in lraq; （2） to evaluate the isolates tolerance to induced drought using polyethylene glycol-6000; （3） assessing genetic diversity and genetic relationships among isolates of natural population with drought tolerant abilities. Drought tolerance study revealed vast variations between Sinorhizobium isolates, the highest tolerant isolates to drought were 12 from total thirty （40%）, tolerated from -3 up to -4 MPa, while the drought sensitive isolates tolerated up to -1.5 MPa, except isolate Bs 58 which tolerated up to -1 Mpa water potential. The growth declined with the increase of drought stress. Cluster analysis based on Polymerase Chain Reaction-Restriction Fragment Length Polymorphism （PCR-RFLP） of the 16S rDNA showed two divergent groups with 41% similarity, the first group included three drought sensitive isolates （Bs 44, Bs 54 and Bs 58）, the second group comprised the rest nine isolates （moderate and high drought tolerant）, except for Bs 55 which was drought sensitive isolate, all isolates in the two groups showed no differences between them. The PCR-RFLP of 16S rDNA method revealed a genetic variance between the drought sensitive and tolerant isolates.展开更多
Several studies have demonstrated that the Rhizobium nifA gene is an activator of nitrogen fixation acting in nodule bacteria. To understand the effects of the Sinorhizobium meliloti nifA gene on Alfalfa, the cDNA-AFL...Several studies have demonstrated that the Rhizobium nifA gene is an activator of nitrogen fixation acting in nodule bacteria. To understand the effects of the Sinorhizobium meliloti nifA gene on Alfalfa, the cDNA-AFLP technique was employed to study the changes in gene expression in nifA mutant nodules. Among the approximately 3,000 transcriptderived fragments, 37 had differential expression levels. These expression levels were subsequently confirmed by reverse Northern blot and RT-polymerase chain reaction. Sequence analyses revealed that 21 cDNA fragments corresponded to genes involved in signal communication, protein degradation, nutrient metabolism, cell growth and development.展开更多
Our previous work showed that an enoyl-ACP reductase gene fabI1 of Sinorhizobium meliloti was down-regulated in the nifA mutant nodule bacteria. To gain a better understanding of fabI1 gene, a single site insertion mu...Our previous work showed that an enoyl-ACP reductase gene fabI1 of Sinorhizobium meliloti was down-regulated in the nifA mutant nodule bacteria. To gain a better understanding of fabI1 gene, a single site insertion mutant was constructed in this study. The fabI1 mutant was retarded in cell growth, and its ability to grow on media with high concentration of NaCl was reduced. In addition, the mutant was completely defective in swarming phenotype. During symbiosis, the fabI1 mutant had delayed nodule formation on host plants. Despite the fact that FabI1 protein showed 66% identity with another enoyl-ACP reductase FabI2 in S. meliloti, defects in fabI1 were not rescued by the plasmidborne version of fabI2. This indicated the different functions of the two FabI proteins in S. meliloti.展开更多
The nifA gene is an important regulatory gene and its product, NifA protein, regulates the expression of many nif genes involved in the nitrogen fixation process. We introduced multiple copies of the constitutively ex...The nifA gene is an important regulatory gene and its product, NifA protein, regulates the expression of many nif genes involved in the nitrogen fixation process. We introduced multiple copies of the constitutively expressed Sinorhizobium meliloti (Sm) or Enterobacter cloacae (Ec) nifA gene into both the nifA mutant strain SmY and the wild-type strain Sm1021. Root nodules produced by SmY containing a constitutively expressed Sm nifA gene were capable of fixing nitrogen, while nodules produced by SmY containing the Ec nifA gene remained unable to fix nitrogen, as is the case for SmY itself. However, transfer of an additional Sm nifA gene into Sm1021 improved the nitrogen-fixing efficiency of root nodules to a greater extent than that observed upon transfer of the Ec nifA gene into Sm1021. Comparative analysis of amino acid sequences between Sm NifA and Ec NifA showed that the N-terminal domain was the least similar, but this domain is indispensable for complementation of the Fix? phenotype of SmY by Sm NifA. We conclude that more than one domain is involved in determining functional differences between Sm NifA and Ec NifA.展开更多
In Sinorhizobium meliloti, the nodD3 gene is transcriptionally controlled by two promot-ers, P1 and P2. Under P1, there is a 660 bp sequence including a small open reading frame, ORF2, followed by the nodD3 coding reg...In Sinorhizobium meliloti, the nodD3 gene is transcriptionally controlled by two promot-ers, P1 and P2. Under P1, there is a 660 bp sequence including a small open reading frame, ORF2, followed by the nodD3 coding region. Genetic analysis using the different deletions on the 3′ends of P1 downstream sequence showed that the downstream sequence +1—+125nt is es-sential for P1 expression. Complementation, mutations and nodulation tests demonstrated that the ORF2 auto-represses P1 expression, while the P1 downstream sequence +1—+125nt counteracts it.展开更多
The existence of multiple adenylate cy- clase encoding genes implies the importance of cAMP in Sinorhizobium meliloti 1021. In this study, as a pioneer step of understanding cAMP roles, mi- croarray analysis on S. mel...The existence of multiple adenylate cy- clase encoding genes implies the importance of cAMP in Sinorhizobium meliloti 1021. In this study, as a pioneer step of understanding cAMP roles, mi- croarray analysis on S. meliloti was carried out for the function of exogenous cAMP. To our surprise, the result showed that the transcriptions of glnII and glnK genes were significantly upshifted in the presence of exogenous cAMP in S. meliloti. This phenomenon is further confirmed in S. meliloti that the expression of either glnII or glnK promoter-lacZ translational fusion is higher in the presence of exogenous cAMP. Therefore, for the first time, we have identified genes from S. meliloti whose expression is activated by cAMP. The potential physiological role of upregula- tion of glnII and glnK by cAMP is discussed.展开更多
The Sinorhizobium meliloti C4-dicarboxylate transport (Dct) system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate per-mease, is expressed in both free living and symbiotic c...The Sinorhizobium meliloti C4-dicarboxylate transport (Dct) system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate per-mease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is abso-lutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5α strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc-curred only at a certain depth under the surface of M63- 0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentra-tions, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regu-lated by oxygen concentration.展开更多
Though the majority of bacteria can form structured communities known as biofilms, mutations can cause bacterial strains to vary in their ability to form a biofilm. In this study, the apparent diffusion coefficient of...Though the majority of bacteria can form structured communities known as biofilms, mutations can cause bacterial strains to vary in their ability to form a biofilm. In this study, the apparent diffusion coefficient of polystyrene microspheres 0.29 μm in diameter, which were executing Brownian motion inside bacterial colonies, was used as a quantitative parameter of the ability of a strain to form a biofilm and of the biofilm development. The study was performed using five Sinorhizobium meliloti strains, the biofilm-forming strains Rm8530 expR+, Rm8530 exoY, and Rm9034 expG, and the non-biofilm forming strains Rm1021 and Rm9030-2 expA1. The green fluorescent beads were placed with each strain in a separate channel of a microfluidic device. Thus, as the bacterial colonies grew under identical conditions over a 4-day period, the motion of the fluorescent microspheres was recorded and the diffusion coefficients were measured every 24 hours via particle tracking algorithms. It was found that each strain displayed a unique pattern of change in diffusion coefficient over time. Also, for a given biofilm-forming strain, there was a clear correlation between the value of the diffusion coefficient and the appearance and motility of the bacterial community. Thus, the diffusion coefficient can be used to identify different S. meliloti strains, and for the biofilm-forming strains, it is also a quantitative indicator of the stage of biofilm development.展开更多
GcvA is a member of the LysR family of transcriptional regulators that mediates the expression of the glycine cleavage (GCV) operon (gcvTHP) in response to glycine in Escherichia coli. In our previous work, 90 putativ...GcvA is a member of the LysR family of transcriptional regulators that mediates the expression of the glycine cleavage (GCV) operon (gcvTHP) in response to glycine in Escherichia coli. In our previous work, 90 putative regulator genes of the LysR family in Sinorhizobium meliloti were mutagenized to determine their phenotype. In the present study, we found that the S. meliloti genome had two gcvA genes, gcvA1 and gcvA2. Both gcvA1 and gcvA2 were required for full activation of the gcvTHP operon in the presence of exogenous glycine. The gcvA1-mediated activation of gcvTHP operon was gly- cine-inducible, while gcvA2-mediated activation was not. We speculate that the regulatory mechanism for gcvTHP expression in S. meliloti differed from E. coli. Evolutionary analysis showed that GcvA were distributed in many genera of Proteobacteria and the distances between GcvA1 and GcvA2 in S. meliloti and GcvA in E. coli were large, which may explain the different regulatory mechanisms for gcvTHP expression. These findings could provide new clues to the role of the LysR gene family.展开更多
基金This work was supported by the National Grand Fundamental Research 973 Project (No. 2001CB108901)National Science Foundation of China (No. 30400267).
文摘Sinorhizobium meliloti nifA is important in fixing nitrogen during symbiosis. A nifA null mutant induces small white invalid nodules in the roots of host plant. The additional phenotypic alterations associated with the disruption of the nifA gene are reported in this study. Under a free-living state, S. meliloti nifA mutant reduces its ability to swarm on a half-solid plate. Interestingly, the AHL （Acylhomoserine lactones） contents in the nifA mutant are lower than that of the wild type during the lag phase, whereas it is reversed in the logarithmic and stationary phases. Quantitative spectrophotometric assays reveal that the total amount of extracellular proteins of the nifA mutant are lower than that of the wild type. In addition, the mutant abolishes its nodulation competitive ability during symbiosis. These findings indicate that NifA plays a regulatory role in multiple cellular processes in S. meliloti.
基金Project supported by the National "Eleventh Five Years Plan" Key Project on Science and Technology (No. 2006BAD02A15)the National Natural Science Foundation of China (No. 30671222).
文摘Seventeen Sinorhizobium meliloti strains from seven provinces in China were used to screen highly effective strains for alfalfa cultivar in a greenhouse study and their symbiotic relationship and competitive ability were studied in the field. CCBAU30138 was the most effective strain, as evidenced by increase in dry weights. A field experiment showed that the inoculation of alfalfa with CCBAU30138 resulted in increases of 11.9% and 19.6% of dry matter production and crude protein production, respectively, in forage of monocultured plants. The total dry matter yields of alfalfa and tall fescue in binary culture were increased by 16.3% by inoculation of alfalfa with this strain. These results showed that S. rneliloti strain CCBAU30138 was an effective inoculant both in the greenhouse and in the field. The analysis of randomly amplified polymorphic DNA （RAPD） by polymerase chain reaction （PCR） from nodule extracts showed that the strain CCBAU30138 had high competitiveness in the field. It occupied 47.5% of nodules in alfalfa monoculture and 44.4% of nodules in alfalfa-tall fescue binary culture after 20 weeks of growth. In conclusion, a simple system to select highly effective and competitive symbiotic strains specific to alfalfa was established. Using this system, a s.train suitable for the alfalfa cultivar ‘Vector＇ grown in Wuqiao County of Hebei Province was obtained.
文摘Alfalfa （Medicago sativa L.） is being grown in harsh environment in Iraq and is mostly subjected to abiotic stresses such as drought, salinity, pH and temperature. Both alfalfa and its nitrogen fixing symbiotic bacteria Sinorhizobium meliloti are affected by these environmental stresses. Enhancing nitrogen fixation biologically could be achieved through selection of tolerant strains of S. meliloti to these environmental stresses and inoculating them to the crop, also growing tolerant cultivars. This study examines phenotypic diversity for tolerance to drought, salinity, temperature and pH. Sixty isolates sampled from different areas of Iraq. The results revealed high degree of phenotypic diversity in Sinorhizobium populations. Furthermore, the isolates which showed tolerance to drought stress also showed tolerance to salinity and high degree of temperature, indicating direct relationship between three physiological path ways. Also 58.3% of drought tolerant isolates were alkaline tolerant they tolerated up to pH 9, point to say almost all drought tolerant isolates in this study illustrated strong ＋ positive reaction to catalase enzyme. And 91.6% themes were negative for Gelatinase enzyme test. While only 50% of drought sensitive isolates were negative for drought sensitive isolates could grow at high temperature （42 ℃）.
文摘Soil bacteria Sinorhizobium meliloti had enormous agricultural value, due to their ability in fixing nitrogen symbiotically with an important forage crop legume--alfalfa. The aims of the present study were （1） to isolate indigenous S. meliloti from different field sites in lraq; （2） to evaluate the isolates tolerance to induced drought using polyethylene glycol-6000; （3） assessing genetic diversity and genetic relationships among isolates of natural population with drought tolerant abilities. Drought tolerance study revealed vast variations between Sinorhizobium isolates, the highest tolerant isolates to drought were 12 from total thirty （40%）, tolerated from -3 up to -4 MPa, while the drought sensitive isolates tolerated up to -1.5 MPa, except isolate Bs 58 which tolerated up to -1 Mpa water potential. The growth declined with the increase of drought stress. Cluster analysis based on Polymerase Chain Reaction-Restriction Fragment Length Polymorphism （PCR-RFLP） of the 16S rDNA showed two divergent groups with 41% similarity, the first group included three drought sensitive isolates （Bs 44, Bs 54 and Bs 58）, the second group comprised the rest nine isolates （moderate and high drought tolerant）, except for Bs 55 which was drought sensitive isolate, all isolates in the two groups showed no differences between them. The PCR-RFLP of 16S rDNA method revealed a genetic variance between the drought sensitive and tolerant isolates.
文摘Several studies have demonstrated that the Rhizobium nifA gene is an activator of nitrogen fixation acting in nodule bacteria. To understand the effects of the Sinorhizobium meliloti nifA gene on Alfalfa, the cDNA-AFLP technique was employed to study the changes in gene expression in nifA mutant nodules. Among the approximately 3,000 transcriptderived fragments, 37 had differential expression levels. These expression levels were subsequently confirmed by reverse Northern blot and RT-polymerase chain reaction. Sequence analyses revealed that 21 cDNA fragments corresponded to genes involved in signal communication, protein degradation, nutrient metabolism, cell growth and development.
基金supported by the National Natural Sciences Foundation of China (Grant No. 30770171)Shanghai Natural Sciences Foundation (Grant No. 05ZR14135)National Key Basic Research and Development Program of China (Grant No. 2001CB108901)
文摘Our previous work showed that an enoyl-ACP reductase gene fabI1 of Sinorhizobium meliloti was down-regulated in the nifA mutant nodule bacteria. To gain a better understanding of fabI1 gene, a single site insertion mutant was constructed in this study. The fabI1 mutant was retarded in cell growth, and its ability to grow on media with high concentration of NaCl was reduced. In addition, the mutant was completely defective in swarming phenotype. During symbiosis, the fabI1 mutant had delayed nodule formation on host plants. Despite the fact that FabI1 protein showed 66% identity with another enoyl-ACP reductase FabI2 in S. meliloti, defects in fabI1 were not rescued by the plasmidborne version of fabI2. This indicated the different functions of the two FabI proteins in S. meliloti.
文摘The nifA gene is an important regulatory gene and its product, NifA protein, regulates the expression of many nif genes involved in the nitrogen fixation process. We introduced multiple copies of the constitutively expressed Sinorhizobium meliloti (Sm) or Enterobacter cloacae (Ec) nifA gene into both the nifA mutant strain SmY and the wild-type strain Sm1021. Root nodules produced by SmY containing a constitutively expressed Sm nifA gene were capable of fixing nitrogen, while nodules produced by SmY containing the Ec nifA gene remained unable to fix nitrogen, as is the case for SmY itself. However, transfer of an additional Sm nifA gene into Sm1021 improved the nitrogen-fixing efficiency of root nodules to a greater extent than that observed upon transfer of the Ec nifA gene into Sm1021. Comparative analysis of amino acid sequences between Sm NifA and Ec NifA showed that the N-terminal domain was the least similar, but this domain is indispensable for complementation of the Fix? phenotype of SmY by Sm NifA. We conclude that more than one domain is involved in determining functional differences between Sm NifA and Ec NifA.
基金This work was supported by the National High Technology 863 Programs of China the 973 Project of the Ministry of Science and Technology (Grant No. 001CB108901) and the fund of the Shanghai Institutes of Biological Sciences.
文摘In Sinorhizobium meliloti, the nodD3 gene is transcriptionally controlled by two promot-ers, P1 and P2. Under P1, there is a 660 bp sequence including a small open reading frame, ORF2, followed by the nodD3 coding region. Genetic analysis using the different deletions on the 3′ends of P1 downstream sequence showed that the downstream sequence +1—+125nt is es-sential for P1 expression. Complementation, mutations and nodulation tests demonstrated that the ORF2 auto-represses P1 expression, while the P1 downstream sequence +1—+125nt counteracts it.
基金This work was supported by the Chinese National Key Program for Basic Research （973） （Grant Nos. 2001CB108902 ＆ 2001CB108903）the National Natural Science Foundation of China （Grant No. 30470940）+1 种基金Bundesministerium fiir Bildung und Forschung, Germany （Grant No. 031U213D）Deutsche Forschungsgemeinschaft （Grant No. BIZ 7）.
文摘The existence of multiple adenylate cy- clase encoding genes implies the importance of cAMP in Sinorhizobium meliloti 1021. In this study, as a pioneer step of understanding cAMP roles, mi- croarray analysis on S. meliloti was carried out for the function of exogenous cAMP. To our surprise, the result showed that the transcriptions of glnII and glnK genes were significantly upshifted in the presence of exogenous cAMP in S. meliloti. This phenomenon is further confirmed in S. meliloti that the expression of either glnII or glnK promoter-lacZ translational fusion is higher in the presence of exogenous cAMP. Therefore, for the first time, we have identified genes from S. meliloti whose expression is activated by cAMP. The potential physiological role of upregula- tion of glnII and glnK by cAMP is discussed.
基金This work was supported by the National Key Basic Research(973)Program of the Ministry of Science and Technology of China(Grant No.2001CB 108903)China-Ireland International Collabo ration Program of the Ministry of Science and Technology of China and Science Foundation of Ireland(Grant No.CI-2003-07)the National Natural Science Foundation of China(Grant No.39925017).
文摘The Sinorhizobium meliloti C4-dicarboxylate transport (Dct) system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate per-mease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is abso-lutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5α strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc-curred only at a certain depth under the surface of M63- 0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentra-tions, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regu-lated by oxygen concentration.
文摘Though the majority of bacteria can form structured communities known as biofilms, mutations can cause bacterial strains to vary in their ability to form a biofilm. In this study, the apparent diffusion coefficient of polystyrene microspheres 0.29 μm in diameter, which were executing Brownian motion inside bacterial colonies, was used as a quantitative parameter of the ability of a strain to form a biofilm and of the biofilm development. The study was performed using five Sinorhizobium meliloti strains, the biofilm-forming strains Rm8530 expR+, Rm8530 exoY, and Rm9034 expG, and the non-biofilm forming strains Rm1021 and Rm9030-2 expA1. The green fluorescent beads were placed with each strain in a separate channel of a microfluidic device. Thus, as the bacterial colonies grew under identical conditions over a 4-day period, the motion of the fluorescent microspheres was recorded and the diffusion coefficients were measured every 24 hours via particle tracking algorithms. It was found that each strain displayed a unique pattern of change in diffusion coefficient over time. Also, for a given biofilm-forming strain, there was a clear correlation between the value of the diffusion coefficient and the appearance and motility of the bacterial community. Thus, the diffusion coefficient can be used to identify different S. meliloti strains, and for the biofilm-forming strains, it is also a quantitative indicator of the stage of biofilm development.
基金Supported by National Basic Research and Development Program of China (Grant No. 2001CB108901)USA NIH (5S06GM8225) PSC-CUNY (617320030 and 632140032)
文摘GcvA is a member of the LysR family of transcriptional regulators that mediates the expression of the glycine cleavage (GCV) operon (gcvTHP) in response to glycine in Escherichia coli. In our previous work, 90 putative regulator genes of the LysR family in Sinorhizobium meliloti were mutagenized to determine their phenotype. In the present study, we found that the S. meliloti genome had two gcvA genes, gcvA1 and gcvA2. Both gcvA1 and gcvA2 were required for full activation of the gcvTHP operon in the presence of exogenous glycine. The gcvA1-mediated activation of gcvTHP operon was gly- cine-inducible, while gcvA2-mediated activation was not. We speculate that the regulatory mechanism for gcvTHP expression in S. meliloti differed from E. coli. Evolutionary analysis showed that GcvA were distributed in many genera of Proteobacteria and the distances between GcvA1 and GcvA2 in S. meliloti and GcvA in E. coli were large, which may explain the different regulatory mechanisms for gcvTHP expression. These findings could provide new clues to the role of the LysR gene family.
