The Experts below are selected from a list of 3147 Experts worldwide ranked by ideXlab platform
Donald A. Phillips - One of the best experts on this subject based on the ideXlab platform.
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biotin and other water soluble vitamins are key growth factors for alfalfa root colonization by rhizobium meliloti 1021
1996Co-Authors: Wolfgang R Streit, Cecillia M. Joseph, Donald A. PhillipsAbstract:Rhizosphere growth limitations imposed on Rhizobium meliloti by availability of biotin, thiamine, and riboflavin were overcome by adding nanomolar amounts of these vitamins. Studies done with R. meliloti 1021 showed that both synthesis and uptake of biotin promote colonization of alfalfa roots. Two lines of evidence indicated that plant-derived biotin normally promotes root colonization: (i) adding avidin significantly (P less than or equal to 0.01) reduced rhizosphere growth of R. meliloti 1021, and (ii) growth of Tn5-induced biotin Auxotrophs still increased 10-fold in the rhizosphere. Synthesis, however, is the more important source of biotin for R. meliloti 1021 because in root colonization tests biotin Auxotrophs competed very poorly with the parent strain. Mutations conferring biotin auxotrophy were closely linked on a single restriction fragment, and one was complemented with the Escherichia coli bio operon. Initial nucleotide sequencing and DNA-DNA hybridization tests showed the biotin synthesis genes in R. meliloti are quite different from those in E. coli.
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biotin and other water soluble vitamins are key growth factors for alfalfa root colonization by rhizobium meliloti 1021
1996Co-Authors: Wolfgang R Streit, Cecillia M. Joseph, Donald A. PhillipsAbstract:Rhizosphere growth limitations imposed on Rhizobium meliloti by availability of biotin, thiamine, and riboflavin were overcome by adding nanomolar amounts of these vitamins. Studies done with R. meliloti 1021 showed that both synthesis and uptake of biotin promote colonization of alfalfa roots. Two lines of evidence indicated that plant-derived biotin normally promotes root colonization: (i) adding avidin significantly (P < or = 0.01) reduced rhizosphere growth of R meliloti 1021, and (ii) growth of Tn5-induced biotin Auxotrophs still increased 10-fold in the rhizosphere. Synthesis, however, is the more important source of biotin for R. meliloti 1021 because in root colonization tests biotin Auxotrophs competed very poorly with the parent strain. Mutations conferring biotin auxotrophy were closely linked on a single restriction fragment, and one was complemented with the Escherichia coli bio operon. Initial nucleotide sequencing and DNA-DNA hybridization tests showed the biotin synthesis genes in R. meliloti are quite different from those in E. coli.
Valeria C Culotta - One of the best experts on this subject based on the ideXlab platform.
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the yeast copper zinc superoxide dismutase and the pentose phosphate pathway play overlapping roles in oxidative stress protection
1996Co-Authors: Kimberly Hudak Slekar, Daniel J Kosman, Valeria C CulottaAbstract:Next Section Abstract In Saccharomyces cerevisiae, loss of cytosolic superoxide dismutase (Sod1) results in several air-dependent mutant phenotypes, including methionine auxotrophy and oxygen sensitivity. Here we report that these two sod1Δ phenotypes were specifically suppressed by elevated expression of the TKL1 gene, encoding transketolase of the pentose phosphate pathway. The apparent connection between Sod1 and the pentose phosphate pathway prompted an investigation of mutants defective in glucose-6-phosphate dehydrogenase (Zwf1), which catalyzes the rate-limiting NADPH-producing step of this pathway. We confirmed that zwf1Δ mutants are methionine Auxotrophs and report that they also are oxygen-sensitive. We determined that a functional ZWF1 gene product was required for TKL1 to suppress sod1Δ, leading us to propose that increased flux through the oxidative reactions of the pentose phosphate pathway can rescue sod1 methionine auxotrophy. To better understand this methionine growth requirement, we examined the sulfur compound requirements of sod1Δ and zwf1Δ mutants, and noted that these mutants exhibit the same apparent defect in sulfur assimilation. Our studies suggest that this defect results from the impaired redox status of aerobically grown sod1 and zwf1 mutants, implicating Sod1 and the pentose phosphate pathway as being critical for maintenance of the cellular redox state.
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the yeast copper zinc superoxide dismutase and the pentose phosphate pathway play overlapping roles in oxidative stress protection
1996Co-Authors: Kimberly Hudak Slekar, Daniel J Kosman, Valeria C CulottaAbstract:In Saccharomyces cerevisiae, loss of cytosolic superoxide dismutase (Sod1) results in several air-dependent mutant phenotypes, including methionine auxotrophy and oxygen sensitivity. Here we report that these two sod1Δ phenotypes were specifically suppressed by elevated expression of the TKL1 gene, encoding transketolase of the pentose phosphate pathway. The apparent connection between Sod1 and the pentose phosphate pathway prompted an investigation of mutants defective in glucose-6-phosphate dehydrogenase (Zwf1), which catalyzes the rate-limiting NADPH-producing step of this pathway. We confirmed that zwf1Δ mutants are methionine Auxotrophs and report that they also are oxygen-sensitive. We determined that a functional ZWF1 gene product was required for TKL1 to suppress sod1Δ, leading us to propose that increased flux through the oxidative reactions of the pentose phosphate pathway can rescue sod1 methionine auxotrophy. To better understand this methionine growth requirement, we examined the sulfur compound requirements of sod1Δ and zwf1Δ mutants, and noted that these mutants exhibit the same apparent defect in sulfur assimilation. Our studies suggest that this defect results from the impaired redox status of aerobically grown sod1 and zwf1 mutants, implicating Sod1 and the pentose phosphate pathway as being critical for maintenance of the cellular redox state.
Wolfgang R Streit - One of the best experts on this subject based on the ideXlab platform.
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biotin and other water soluble vitamins are key growth factors for alfalfa root colonization by rhizobium meliloti 1021
1996Co-Authors: Wolfgang R Streit, Cecillia M. Joseph, Donald A. PhillipsAbstract:Rhizosphere growth limitations imposed on Rhizobium meliloti by availability of biotin, thiamine, and riboflavin were overcome by adding nanomolar amounts of these vitamins. Studies done with R. meliloti 1021 showed that both synthesis and uptake of biotin promote colonization of alfalfa roots. Two lines of evidence indicated that plant-derived biotin normally promotes root colonization: (i) adding avidin significantly (P less than or equal to 0.01) reduced rhizosphere growth of R. meliloti 1021, and (ii) growth of Tn5-induced biotin Auxotrophs still increased 10-fold in the rhizosphere. Synthesis, however, is the more important source of biotin for R. meliloti 1021 because in root colonization tests biotin Auxotrophs competed very poorly with the parent strain. Mutations conferring biotin auxotrophy were closely linked on a single restriction fragment, and one was complemented with the Escherichia coli bio operon. Initial nucleotide sequencing and DNA-DNA hybridization tests showed the biotin synthesis genes in R. meliloti are quite different from those in E. coli.
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biotin and other water soluble vitamins are key growth factors for alfalfa root colonization by rhizobium meliloti 1021
1996Co-Authors: Wolfgang R Streit, Cecillia M. Joseph, Donald A. PhillipsAbstract:Rhizosphere growth limitations imposed on Rhizobium meliloti by availability of biotin, thiamine, and riboflavin were overcome by adding nanomolar amounts of these vitamins. Studies done with R. meliloti 1021 showed that both synthesis and uptake of biotin promote colonization of alfalfa roots. Two lines of evidence indicated that plant-derived biotin normally promotes root colonization: (i) adding avidin significantly (P < or = 0.01) reduced rhizosphere growth of R meliloti 1021, and (ii) growth of Tn5-induced biotin Auxotrophs still increased 10-fold in the rhizosphere. Synthesis, however, is the more important source of biotin for R. meliloti 1021 because in root colonization tests biotin Auxotrophs competed very poorly with the parent strain. Mutations conferring biotin auxotrophy were closely linked on a single restriction fragment, and one was complemented with the Escherichia coli bio operon. Initial nucleotide sequencing and DNA-DNA hybridization tests showed the biotin synthesis genes in R. meliloti are quite different from those in E. coli.
Kimberly Hudak Slekar - One of the best experts on this subject based on the ideXlab platform.
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the yeast copper zinc superoxide dismutase and the pentose phosphate pathway play overlapping roles in oxidative stress protection
1996Co-Authors: Kimberly Hudak Slekar, Daniel J Kosman, Valeria C CulottaAbstract:Next Section Abstract In Saccharomyces cerevisiae, loss of cytosolic superoxide dismutase (Sod1) results in several air-dependent mutant phenotypes, including methionine auxotrophy and oxygen sensitivity. Here we report that these two sod1Δ phenotypes were specifically suppressed by elevated expression of the TKL1 gene, encoding transketolase of the pentose phosphate pathway. The apparent connection between Sod1 and the pentose phosphate pathway prompted an investigation of mutants defective in glucose-6-phosphate dehydrogenase (Zwf1), which catalyzes the rate-limiting NADPH-producing step of this pathway. We confirmed that zwf1Δ mutants are methionine Auxotrophs and report that they also are oxygen-sensitive. We determined that a functional ZWF1 gene product was required for TKL1 to suppress sod1Δ, leading us to propose that increased flux through the oxidative reactions of the pentose phosphate pathway can rescue sod1 methionine auxotrophy. To better understand this methionine growth requirement, we examined the sulfur compound requirements of sod1Δ and zwf1Δ mutants, and noted that these mutants exhibit the same apparent defect in sulfur assimilation. Our studies suggest that this defect results from the impaired redox status of aerobically grown sod1 and zwf1 mutants, implicating Sod1 and the pentose phosphate pathway as being critical for maintenance of the cellular redox state.
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the yeast copper zinc superoxide dismutase and the pentose phosphate pathway play overlapping roles in oxidative stress protection
1996Co-Authors: Kimberly Hudak Slekar, Daniel J Kosman, Valeria C CulottaAbstract:In Saccharomyces cerevisiae, loss of cytosolic superoxide dismutase (Sod1) results in several air-dependent mutant phenotypes, including methionine auxotrophy and oxygen sensitivity. Here we report that these two sod1Δ phenotypes were specifically suppressed by elevated expression of the TKL1 gene, encoding transketolase of the pentose phosphate pathway. The apparent connection between Sod1 and the pentose phosphate pathway prompted an investigation of mutants defective in glucose-6-phosphate dehydrogenase (Zwf1), which catalyzes the rate-limiting NADPH-producing step of this pathway. We confirmed that zwf1Δ mutants are methionine Auxotrophs and report that they also are oxygen-sensitive. We determined that a functional ZWF1 gene product was required for TKL1 to suppress sod1Δ, leading us to propose that increased flux through the oxidative reactions of the pentose phosphate pathway can rescue sod1 methionine auxotrophy. To better understand this methionine growth requirement, we examined the sulfur compound requirements of sod1Δ and zwf1Δ mutants, and noted that these mutants exhibit the same apparent defect in sulfur assimilation. Our studies suggest that this defect results from the impaired redox status of aerobically grown sod1 and zwf1 mutants, implicating Sod1 and the pentose phosphate pathway as being critical for maintenance of the cellular redox state.
David J Bzik - One of the best experts on this subject based on the ideXlab platform.
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Rhoptry proteins ROP5, ROP17, and ROP18 are required for the antitumor response.
2016Co-Authors: Barbara A Fox, Kiah L. Sanders, Leah M. Rommereim, Rebekah B. Guevara, David J BzikAbstract:(A) ID8DV ovarian tumors were established in C57BL/6 mice and groups of mice were treated with PBS, or were vaccinated i.p. with tachyzoites of uracil Auxotrophs (OMP), or were vaccinated i.p. with uracil Auxotrophs (OMP) lacking rhoptry proteins ROP5, ROP17, or ROP18 using the three-dose treatment schedule. (B) Mouse embryonic fibroblasts were stimulated with IFN-γ and parasite survival (measured as PFU) was determined for uracil Auxotrophs mutants lacking specific rhoptry or dense granule proteins. (C) Relative parasite invasion efficiency of uracil Auxotrophs was measured in MEFs. The parasite to PFU ratios (invasion efficiency) was measured in at least 4 independent assays and compared to the invasion efficiency of the parental OMP strain. (D) ID8DV ovarian tumors were established in C57BL/6 mice and groups of mice were treated with PBS, or were vaccinated i.p. with tachyzoites of type I uracil Auxotrophs (OMP), or were vaccinated i.p. with type II OMP, or were vaccinated i.p. with type II strains lacking ROP5 or ROP18 using the three-dose treatment schedule. Data is representative of at least two independent experiments. ns was not significant, *p
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Immunity to T. gondii does not diminish the potency of the antitumor response stimulated by uracil Auxotrophs.
2016Co-Authors: Barbara A Fox, Kiah L. Sanders, Leah M. Rommereim, Rebekah B. Guevara, David J BzikAbstract:(A) ID8DV ovarian tumors were established in C57BL/6 mice and groups of mice were treated with phosphate buffered saline (PBS) or mice were vaccinated i.p. with tachyzoites (the acute replicative form of T. gondii) of uracil Auxotrophs (OMP [13] or CPS [5]) at 8, 20, and 32 d after tumor challenge (the three-dose treatment schedule). (B) ID8DV ovarian tumors were established in C57BL/6 mice and groups of mice were treated with PBS or were vaccinated once (8 d), twice (8, 20 d), three times (8, 20, 32 d), or five times (8, 20, 32, 44, 56 d) i.p. with tachyzoites of uracil Auxotrophs. (C) Groups of C57BL/6 mice were vaccinated (VAC) with uracil Auxotrophs to establish protective immunity or mice were treated with PBS (naive). Twelve months later ID8DV tumors were established in vaccinated or age matched naive mice and tumors were treated with PBS or were vaccinated with uracil Auxotrophs using the three-dose treatment schedule. Data is representative of at least two independent experiments. ns was not significant, *p
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avirulent uracil Auxotrophs based on disruption of orotidine 5 monophosphate decarboxylase elicit protective immunity to toxoplasma gondii
2010Co-Authors: Barbara A Fox, David J BzikAbstract:The orotidine-5'-monophosphate decarboxylase (OMPDC) gene, encoding the final enzyme of the de novo pyrimidine biosynthesis pathway, was deleted using Toxoplasma gondii KU80 knockouts to develop an avirulent nonreverting pyrimidine auxotroph strain. Additionally, to functionally address the role of the pyrimidine salvage pathway, the uridine phosphorylase (UP) salvage activity was knocked out and a double knockout of UP and OMPDC was also constructed. The nonreverting DeltaOMPDC, DeltaUP, and DeltaOMPDC DeltaUP knockout strains were evaluated for pyrimidine auxotrophy, for attenuation of virulence, and for their ability to elicit potent immunity to reinfection. The DeltaUP knockout strain was replication competent and virulent. In contrast, the DeltaOMPDC and DeltaOMPDC DeltaUP strains were uracil Auxotrophs that rapidly lost their viability during pyrimidine starvation. Replication of the DeltaOMPDC strain but not the DeltaOMPDC DeltaUP strain was also partially rescued in vitro with uridine or cytidine supplementation. Compared to their hypervirulent parental type I strain, the DeltaOMPDC and DeltaOMPDC DeltaUP knockout strains exhibited extreme attenuation in murine virulence (approximately 8 logs). Genetic complementation of the DeltaOMPDC strain using a functional OMPDC allele restored normal replication and type I parental strain virulence phenotypes. A single immunization of mice with either the live critically attenuated DeltaOMPDC strain or the DeltaOMPDC DeltaUP knockout strain effectively induced potent protective immunity to lethal challenge infection. The avirulent nonreverting DeltaOMPDC and DeltaOMPDC DeltaUP strains provide new tools for the dissection of the host response to infection and are promising candidates for safe and effective Th1 vaccine platforms that can be easily genetically engineered.
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de novo pyrimidine biosynthesis is required for virulence of toxoplasma gondii
2002Co-Authors: David J BzikAbstract:Toxoplasma gondii is a ubiquitous protozoan parasite that is responsible for severe congenital birth defects and fatal toxoplasmic encephalitis in immunocompromized people1. Fundamental aspects of obligate intracellular replication and pathogenesis are only now beginning to emerge for protozoan parasites. T. gondii has a fragmented pathway for salvaging pyrimidine nucleobases derived from the parasite or host cell, and this limited pyrimidine salvage capacity is funnelled exclusively through uracil phosphoribosyltransferase2,3. Disrupting the function of this enzyme does not affect the growth of T. gondii tachyzoites4, which suggests that the de novo pyrimidine biosynthesis pathway may be necessary for growth. We have examined the virulence of T. gondii mutants that lack carbamoyl phosphate synthetase II (uracil Auxotrophs) to determine whether de novo pyrimidine biosynthesis is required in vivo. Here we show that T. gondii uracil Auxotrophs are completely avirulent not only in immune-competent BALB/c mice but also in mice that lack interferon-γ. A single injection of the uracil auxotroph into BALB/c mice induces long-term protective immunity to toxoplasmosis. Our findings indicate the significance of the de novo pyrimidine biosynthesis pathway for the virulence of parasitic protozoa, and suggest routes for developing vaccines and chemotherapy.