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Biomedical subjects

A Pühler

Publications and source records attributed to A Pühler.

At least 19 recordsLinked to original sources
PubMed2006

Long-term field release of bioluminescent Sinorhizobium meliloti strains to assess the influence of a recA mutation on the strains' survival.

A field release experiment was carried out to study the fate of the isogenic, firefly luciferase (luc) gene-tagged Sinorhizobium meliloti strains L1 (RecA-) and L33 (RecA+) in the environment. Both strains were released at concentrations of approximately 10(6) cfu g(-1) soil in replicate and randomized field plots, which had been sown with alfalfa (Medicago sativa). The survival of both strains during the following 7 years could be subdivided into three phases: a sharp decline for more than two orders of magnitude within the first 4 months (phase I), followed by fluctuations around an average number of 10(4) cfu g(-1) soil for nearly 4 years (phase II), and a further decline to approximately 60 cfu g(-1) (phase III). At most sampling dates, no significant differences in the survival of both strains were detected, indicating that the recA gene function was dispensable under these environmental conditions. During the field inoculation, both strains were dispersed accidentally by wind in small numbers to noninoculated field plots. Strain L33 established at a concentration of more than 10(3) cfu g(-1) soil with subsequent seasonal fluctuations. Although strain L1 must have been disseminated to a similar extent, it could never be recovered from noninoculated field plots, indicating that the recA mutation interfered with the strain's capability to establish there. At the beginning of the field experiment, an indigenous alfalfa-nodulating population was below the limit of detection. In the following years, however, an indigenous population arose, which finally outcompeted both strains for saprophytic growth and alfalfa nodulation. RecA- strain L1 was outcompeted for alfalfa nodulation slightly faster than its RecA+ counterpart L33. The diversity of the indigenous population was characterized by employing the Enterobacterial Repetitive Intergenic Consensus polymerase chain reaction fingerprint method. Typing of 2731 root nodule isolates revealed a total of 38 fingerprint groups. More than 80% of the isolates could be grouped into six dominant fingerprint groups, indicating that a few dominant bacterial strain types had outcompeted the released strains.

Air Microbiology↗
PubMed2006

Sequence analysis of the 144-kilobase accessory plasmid pSmeSM11a, isolated from a dominant Sinorhizobium meliloti strain identified during a long-term field release experiment.

The genome of Sinorhizobium meliloti type strain Rm1021 consists of three replicons: the chromosome and two megaplasmids, pSymA and pSymB. Additionally, many indigenous S. meliloti strains possess one or more smaller plasmids, which represent the accessory genome of this species. Here we describe the complete nucleotide sequence of an accessory plasmid, designated pSmeSM11a, that was isolated from a dominant indigenous S. meliloti subpopulation in the context of a long-term field release experiment with genetically modified S. meliloti strains. Sequence analysis of plasmid pSmeSM11a revealed that it is 144,170 bp long and has a mean G+C content of 59.5 mol%. Annotation of the sequence resulted in a total of 160 coding sequences. Functional predictions could be made for 43% of the genes, whereas 57% of the genes encode hypothetical or unknown gene products. Two plasmid replication modules, one belonging to the repABC replicon family and the other belonging to the plasmid type A replicator region family, were identified. Plasmid pSmeSM11a contains a mobilization (mob) module composed of the type IV secretion system-related genes traG and traA and a putative mobC gene. A large continuous region that is about 42 kb long is very similar to a corresponding region located on S. meliloti Rm1021 megaplasmid pSymA. Single-base-pair deletions in the homologous regions are responsible for frameshifts that result in nonparalogous coding sequences. Plasmid pSmeSM11a carries additional copies of the nodulation genes nodP and nodQ that are responsible for Nod factor sulfation. Furthermore, a tauD gene encoding a putative taurine dioxygenase was identified on pSmeSM11a. An acdS gene located on pSmeSM11a is the first example of such a gene in S. meliloti. The deduced acdS gene product is able to deaminate 1-aminocyclopropane-1-carboxylate and is proposed to be involved in reducing the phytohormone ethylene, thus influencing nodulation events. The presence of numerous insertion sequences suggests that these elements mediated acquisition of accessory plasmid modules.

Agrobacterium tumefaciens↗
PubMed2005

The 120 592 bp IncF plasmid pRSB107 isolated from a sewage-treatment plant encodes nine different antibiotic-resistance determinants, two iron-acquisition systems and other putative virulence-associated functions.

The antibiotic-multiresistance IncF plasmid pRSB107 was isolated by a transformation-based approach from activated-sludge bacteria of a wastewater-treatment plant. It confers resistance to ampicillin, penicillin G, chloramphenicol, erythromycin, kanamycin, neomycin, streptomycin, sulfonamides, tetracycline and trimethoprim and against mercuric ions. Complete sequencing of this plasmid revealed that it is 120 592 bp in size and has a G+C content of 53.1 mol%. The plasmid backbone is composed of three replicons, RepFIA, RepFIB and RepFII, which are almost identical to corresponding regions located on the F-plasmid and on R100. The three replicons encode replication initiation (rep) and replication control, multimer resolution (mrs), post-segregational killing of plasmid-free cells (psk) and active plasmid partitioning (sopABC locus). Part of the F-leading region and remnants of the F-homologous DNA-transfer (tra) module complete the pRSB107 backbone. Plasmid pRSB107 contains a complex, highly mosaic 35 991 bp antibiotic-resistance region consisting of a Tn21- and a Tn10-derivative and a chloramphenicol-resistance module. The Tn21 derivative is composed of a mercury-resistance region (mer), a Tn4352B-like kanamycin/neomycin-resistance transposon, a streptomycin/sulfonamide-resistance module, remnants of the beta-lactam-resistance transposon Tn1, a macrolide-resistance module flanked by copies of IS26 and IS6100, remnants of Tn402 integrating a class 1 integron and the Tn21-specific transposition module. A truncated version of the tetracycline-resistance transposon Tn10 and the chloramphenicol acetyltransferase gene catA complete the pRSB107 resistance region. In addition to antibiotic resistance, pRSB107 encodes the following putative virulence-associated functions: (i) an aerobactin iron-acquisition siderophore system (iuc/iut); (ii) a putative high-affinity Fe(2+) uptake system which was previously identified on a pathogenicity island of Yersinia pestis and in the genome of the phytopathogen Erwinia carotovora subsp. atroseptica SCRI1043; (iii) an sn-glycerol-3-phosphate transport system (ugp); and (iv) the virulence-associated genes vagCD having a possible function in stable plasmid inheritance. All the accessory modules are framed by insertion sequences, indicating that pRSB107 was gradually assembled by integration of different horizontally acquired DNA segments via transposition or homologous recombination.

Base Composition↗
PubMed2005

Role of the ssu and seu genes of Corynebacterium glutamicum ATCC 13032 in utilization of sulfonates and sulfonate esters as sulfur sources.

Corynebacterium glutamicum ATCC 13032 was found to be able to utilize a broad range of sulfonates and sulfonate esters as sulfur sources. The two gene clusters potentially involved in sulfonate utilization, ssuD1CBA and ssuI-seuABC-ssuD2, were identified in the genome of C. glutamicum ATCC 13032 by similarity searches. While the ssu genes encode proteins resembling Ssu proteins from Escherichia coli or Bacillus subtilis, the seu gene products exhibited similarity to the dibenzothiophene-degrading Dsz monooxygenases of Rhodococcus strain IGTS8. Growth tests with the C. glutamicum wild-type and appropriate mutant strains showed that the clustered genes ssuC, ssuB, and ssuA, putatively encoding the components of an ABC-type transporter system, are required for the utilization of aliphatic sulfonates. In C. glutamicum sulfonates are apparently degraded by sulfonatases encoded by ssuD1 and ssuD2. It was also found that the seu genes seuA, seuB, and seuC can effectively replace ssuD1 and ssuD2 for the degradation of sulfonate esters. The utilization of all sulfonates and sulfonate esters tested is dependent on a novel putative reductase encoded by ssuI. Obviously, all monooxygenases encoded by the ssu and seu genes, including SsuD1, SsuD2, SeuA, SeuB, and SeuC, which are reduced flavin mononucleotide dependent according to sequence similarity, have SsuI as an essential component. Using real-time reverse transcription-PCR, the ssu and seu gene cluster was found to be expressed considerably more strongly during growth on sulfonates and sulfonate esters than during growth on sulfate.

Bacterial Proteins↗
PubMed2004

Detection and manipulation of biomolecules by magnetic carriers.

The detection and manipulation of single molecules on a common platform would be of great interest for basic research of biological or chemical systems. A promising approach is the application of magnetic carriers. The principles are demonstrated in this contribution. It is shown that paramagnetic beads can be detected by highly sensitive magnetoresistive sensors yielding a purely electronic signal. Different configurations are discussed. The capability of the sensors to detect even single markers is demonstrated by a model experiment. In addition, the paramagnetic beads can be used as carriers for biomolecules. They can be manipulated on-chip via currents running through specially designed line patterns. Thus, magnetic markers in combination with magnetoresistive sensors are a promising choice for future integrated lab-on-a-chip systems.

Biopolymers↗
PubMed2004

Absence of intrinsic electric conductivity in single dsDNA molecules.

The intrinsic dc conductivity of long, individual lambda phage dsDNA molecules has been investigated by ultrasensitive low current-voltage-spectroscopy (IV) under ambient conditions and controlled low humidity inert gas atmosphere on microfabricated metal-insulator-metal gap structures. We found a strong dependence of the measured conductivity on the apparent humidity, which we attribute to capillary condensation of water to the immobilized DNA molecules, giving rise to additional ionic currents. Additional IV-spectroscopy experiments under controlled argon atmosphere always revealed a significant drop in electrical conductivity to 4 x 10(-15)AV(-1)microm(-1), indicating almost no considerable contribution of electrical long range charge transport.

Bacteriophage lambda↗
PubMed2004

A Rab-related small GTP binding protein is predominantly expressed in root nodules of Medicago sativa.

Rab-related small GTP-binding proteins are known to be involved in the regulation of the vesicular transport system in eucaryotic cells. In this paper we report the isolation of the cDNA clone MS- rab11f from Medicago sativa (alfalfa) root nodules using a combination of RT-PCR and SSCP analysis. MS- rab11f shows high homology to the Rab-related cDNA clone LJ- rab11f from Lotus japonicus root nodules. The MS-Rab11F protein expressed in Escherichia coli was found to bind GTP, confirming that the isolated cDNA indeed codes for a small GTP-binding protein. Expression analysis by RT-PCR demonstrated that MS- rab11f is preferentially expressed in root nodules of alfalfa. Using the cDNA-sequence of MS-rab11f, a peptide-specific antibody was generated. Western blot analysis with this antibody revealed that two Rab11F isoforms, designated MS-Rab11FA and MS-Rab11FB, are found in M. sativa root nodules.

Amino Acid Sequence↗
PubMed2004

Comparison of a prototype magnetoresistive biosensor to standard fluorescent DNA detection.

We present a comparative analysis of a magnetoresistive biosensor to standard fluorescent DNA detection. The biosensor consists of giant magnetoresistive (GMR) type Cu/Ni(80)Fe(20) multilayers in the second antiferromagnetic coupling maximum. Each of the 206 elements of the magnetoresistive biosensor is patterned into a spiral-shaped line that can cover the area of a typical DNA spot (70 microm diameter). The probe DNA is assembled on top of the sensor elements in different concentrations ranging from 16 pg/microl to 10 ng/microl. Complementary biotin-labeled analyte DNA is hybridized to the probe DNA at a concentration of 10 ng/microl. A number of different commercially available magnetic microspheres are investigated to determine the most appropriate markers. The experimental comparison shows that the relative sensitivity of the magnetoresistive biosensor is superior to the fluorescent detection at low probe DNA concentrations.

Biosensing Techniques↗
PubMed2004

The complete sequences of plasmids pB2 and pB3 provide evidence for a recent ancestor of the IncP-1beta group without any accessory genes.

The nucleotide sequences of the broad-host-range antibiotic resistance plasmids pB2 (61 kb) and pB3 (56 kb), which were isolated from a wastewater treatment plant, were determined and analysed. Both have a nearly identical IncP-1beta backbone, which diverged early from the sequenced IncP-1beta plasmids R751, pB10, pJP4, pADP1 and pUO1. In contrast to the latter plasmids, the pB2 and pB3 backbone does not seem to have undergone any deletions. The complete partition gene parA is located downstream of the mating pair formation (trb) module. A 14.4 kb or 19.0 kb mobile genetic element is present between traC and parA of pB3 and pB2, respectively. This region is typical for insertions in IncP-1beta plasmids, but the insertion site is unique. Both elements differ only by a duplication in pB2 of a tetA(C)-tetR-tnpA(IS26) fragment. The 5 bp target site duplication and the 26 bp inverted repeats flanking the mobile genetic elements are still intact, indicating that the insertion occurred recently. The element consists of three nested transposable elements: (i) a relict of a Tn402-like transposon with a gene for a new class D beta-lactamase (bla(NPS-2)); (ii) within that, another Tn402-like element with a class 1 integron harbouring the gene cassettes cmlA1 for a chloramphenicol efflux protein and aadA2 encoding a streptomycin/spectinomycin adenylyltransferase, and a copy of IS6100; (iii) into the integrase gene intI1 a tetracycline resistance module tetA(C)-tetR flanked by copies of IS26 is inserted. Interestingly, in contrast to all other IncP-1beta plasmids analysed so far, the oriV region between trfA and klcA is not interrupted by accessory genes, and there is no indication that previously inserted accessory genes have subsequently been deleted. The genes kluAB are also missing in that region and should thus be considered acquired genes. These findings, together with the fact that IncP-1beta plasmids acquired accessory elements at various positions in the backbone, suggest that IncP-1beta plasmids without any accessory genes exist in microbial communities. They must occasionally acquire accessory genes by transposition events, resulting in those plasmids that have been found based on selectable phenotypic traits.

Antiporters↗
PubMed2003

Comparison of two Xanthomonas campestris pathovar campestris genomes revealed differences in their gene composition.

For the Xanthomonas campestris pathovar campestris wild-type strain B100 a plasmid-based clone library was constructed. The plasmids carried chromosomal fragments of 3-4 kb in size that were tagged in vitro with the artificial transposon KAN-2. More than 3000 of the transposon target sites were characterized by DNA sequencing. The sequences obtained were compared to the recently published genome of Xanthomonas campestris pathovar campestris strain ATCC 33913. Most of the sequenced clones derived from strain B100 matched the chromosomal sequence of strain ATCC 33913. An alignment to the circular map of this chromosome revealed that the similarities were statistically distributed over the entire genome of strain ATCC 33913. The similarity was obvious for protein coding sequences, as well as for mobile genetic elements. However, four regions in the genome of Xanthomonas campestris pathovar campestris strain ATCC 33913, ranging in size from 11 to 37 kb, were not represented in the sequenced clone library of Xanthomonas campestris pathovar campestris strain B100. On the other hand, 1.2% of the sequenced clones originating from Xanthomonas campestris pathovar campestris strain B100 showed no or insignificant similarities to the genome of strain ATCC 33913.

Chromosome Mapping↗
PubMed2003

Genome-wide analysis of the L-methionine biosynthetic pathway in Corynebacterium glutamicum by targeted gene deletion and homologous complementation.

The genome sequence of Corynebacterium glutamicum, a gram-positive soil bacterium widely used as an amino acid producer, was analyzed by a similarity-based approach to elucidate the pathway for the biosynthesis of L-methionine. The functions of candidate ORFs were derived by gene deletion and, if necessary, by homologous complementation of suitable mutants. Of nine candidate ORFs (four of which were known previously), seven ORFs (cg0754 (metX), cg0755 (metY), cg1290 (metE), cg1702 (metH), cg2383 (metF), cg2536 (aecD), and cg2687 (metB)) were demonstrated to be part of the pathway while two others (cg0961 and cg3086) could be excluded. C. glutamicum synthesizes methionine in three, respectively four steps, starting from homoserine. C. glutamicum possesses two genes with similarity to homoserine acetyltransferases but only MetX can act as such while Cg0961 catalyzes a different, unknown reaction. For the incorporation of the sulfur moiety, the known functions of MetY and MetB could be confirmed and AecD was proven to be the only functional cystathionine beta-lyase in C. glutamicum, while Cg3086 can act neither as cystathionine gamma-synthase nor as cystathionine beta-lyase. Finally, MetE and MetH, which catalyze the conversion of L-homocysteine to L-methionine, could be newly identified, together with MetF which provides the necessary N(5)-methyltetrahydrofolate.

Amino Acid Sequence↗
PubMed2003

The 79,370-bp conjugative plasmid pB4 consists of an IncP-1beta backbone loaded with a chromate resistance transposon, the strA-strB streptomycin resistance gene pair, the oxacillinase gene bla(NPS-1), and a tripartite antibiotic efflux system of the resistance-nodulation-division family.

Plasmid pB4 is a conjugative antibiotic resistance plasmid, originally isolated from a microbial community growing in activated sludge, by means of an exogenous isolation method with Pseudomonas sp. B13 as recipient. We have determined the complete nucleotide sequence of pB4. The plasmid is 79,370 bp long and contains at least 81 complete coding regions. A suite of coding regions predicted to be involved in plasmid replication, plasmid maintenance, and conjugative transfer revealed significant similarity to the IncP-1beta backbone of R751. Four resistance gene regions comprising mobile genetic elements are inserted in the IncP-1beta backbone of pB4. The modular 'gene load' of pB4 includes (1) the novel transposon Tn 5719 containing genes characteristic of chromate resistance determinants, (2) the transposon Tn 5393c carrying the widespread streptomycin resistance gene pair strA-strB, (3) the beta-lactam antibiotic resistance gene bla(NPS-1) flanked by highly conserved sequences characteristic of integrons, and (4) a tripartite antibiotic resistance determinant comprising an efflux protein of the resistance-nodulation-division (RND) family, a periplasmic membrane fusion protein (MFP), and an outer membrane factor (OMF). The components of the RND-MFP-OMF efflux system showed the highest similarity to the products of the mexCD-oprJ determinant from the Pseudomonas aeruginosa chromosome. Functional analysis of the cloned resistance region from pB4 in Pseudomonas sp. B13 indicated that the RND-MFP-OMF efflux system conferred high-level resistance to erythromycin and roxithromycin resistance on the host strain. This is the first example of an RND-MFP-OMF-type antibiotic resistance determinant to be found in a plasmid genome. The global genetic organization of pB4 implies that its gene load might be disseminated between bacteria in different habitats by the combined action of the conjugation apparatus and the mobility of its component elements.

Bacterial Proteins↗
PubMed2003

The 64 508 bp IncP-1beta antibiotic multiresistance plasmid pB10 isolated from a waste-water treatment plant provides evidence for recombination between members of different branches of the IncP-1beta group.

The complete 64508 bp nucleotide sequence of the IncP-1beta antibiotic-resistance plasmid pB10, which was isolated from a waste-water treatment plant in Germany and mediates resistance against the antimicrobial agents amoxicillin, streptomycin, sulfonamides and tetracycline and against mercury ions, was determined and analysed. A typical class 1 integron with completely conserved 5' and 3' segments is inserted between the tra and trb regions. The two mobile gene cassettes of this integron encode a beta-lactamase of the oxacillin-hydrolysing type (Oxa-2) and a gene product of unknown function (OrfE-like), respectively. The pB10-specific gene load present between the replication module (trfA1) and the origin of vegetative replication (oriV) is composed of four class II (Tn3 family) transposable elements: (i). a Tn501-like mercury-resistance (mer) transposon downstream of the trfA1 gene, (ii). a truncated derivative of the widespread streptomycin-resistance transposon Tn5393c, (iii). the insertion sequence element IS1071 and (iv). a Tn1721-like transposon that contains the tetracycline-resistance genes tetA and tetR. A very similar Tn501-like mer transposon is present in the same target site of the IncP-1beta degradative plasmid pJP4 and the IncP-1beta resistance plasmid R906, suggesting that pB10, R906 and pJP4 are derivatives of a common ancestor. Interestingly, large parts of the predicted pB10 restriction map, except for the tetracycline-resistance determinant, are identical to that of R906. It thus appears that plasmid pB10 acquired as many as five resistance genes via three transposons and one integron, which it may rapidly spread among bacterial populations given its high promiscuity. Comparison of the pB10 backbone DNA sequences with those of other sequenced IncP-1beta plasmids reveals a mosaic structure. While the conjugative transfer modules (trb and tra regions) and the replication module are very closely related to the corresponding segments of the IncP-1beta resistance plasmid R751 and even more similar to the IncP-1beta degradative plasmids pTSA and pADP-1, the stable inheritance operons klcAB-korC and kleAEF are most similar to those of the IncP-1beta resistance plasmid pB4, and clearly less similar to the other IncP-1beta plasmids. This suggests that IncP-1beta plasmids can undergo recombination in the environment, which may enhance plasmid diversity and bacterial adaptability.

Anti-Bacterial Agents↗
PubMed2001

The genetic organization and evolution of the broad host range mercury resistance plasmid pSB102 isolated from a microbial population residing in the rhizosphere of alfalfa.

Employing the biparental exogenous plasmid isolation method, conjugative plasmids conferring mercury resistance were isolated from the microbial community of the rhizosphere of field grown alfalfa plants. Five different plasmids were identified, designated pSB101-pSB105. One of the plasmids, pSB102, displayed broad host range (bhr) properties for plasmid replication and transfer unrelated to the known incompatibility (Inc) groups of bhr plasmids IncP-1, IncW, IncN and IncA/C. Nucleotide sequence analysis of plasmid pSB102 revealed a size of 55 578 bp. The transfer region of pSB102 was predicted on the basis of sequence similarity to those of other plasmids and included a putative mating pair formation apparatus most closely related to the type IV secretion system encoded on the chromosome of the mammalian pathogen Brucella sp. The region encoding replication and maintenance functions comprised genes exhibiting different degrees of similarity to RepA, KorA, IncC and KorB of bhr plasmids pSa (IncW), pM3 (IncP-9), R751 (IncP-1beta) and RK2 (IncP-1alpha), respectively. The mercury resistance determinants were located on a transposable element of the Tn5053 family designated Tn5718. No putative functions could be assigned to a quarter of the coding capacity of pSB102 on the basis of comparisons with database entries. The genetic organization of the pSB102 transfer region revealed striking similarities to plasmid pXF51 of the plant pathogen Xylella fastidiosa.

Bacteria↗
PubMed2001

Analysis of the chromosome sequence of the legume symbiont Sinorhizobium meliloti strain 1021.

Sinorhizobium meliloti is an alpha-proteobacterium that forms agronomically important N(2)-fixing root nodules in legumes. We report here the complete sequence of the largest constituent of its genome, a 62.7% GC-rich 3,654,135-bp circular chromosome. Annotation allowed assignment of a function to 59% of the 3,341 predicted protein-coding ORFs, the rest exhibiting partial, weak, or no similarity with any known sequence. Unexpectedly, the level of reiteration within this replicon is low, with only two genes duplicated with more than 90% nucleotide sequence identity, transposon elements accounting for 2.2% of the sequence, and a few hundred short repeated palindromic motifs (RIME1, RIME2, and C) widespread over the chromosome. Three regions with a significantly lower GC content are most likely of external origin. Detailed annotation revealed that this replicon contains all housekeeping genes except two essential genes that are located on pSymB. Amino acid/peptide transport and degradation and sugar metabolism appear as two major features of the S. meliloti chromosome. The presence in this replicon of a large number of nucleotide cyclases with a peculiar structure, as well as of genes homologous to virulence determinants of animal and plant pathogens, opens perspectives in the study of this bacterium both as a free-living soil microorganism and as a plant symbiont.

Bacterial Proteins↗
PubMed2001

The complete sequence of the 1,683-kb pSymB megaplasmid from the N2-fixing endosymbiont Sinorhizobium meliloti.

Analysis of the 1,683,333-nt sequence of the pSymB megaplasmid from the symbiotic N(2)-fixing bacterium Sinorhizobium meliloti revealed that the replicon has a high gene density with a total of 1,570 protein-coding regions, with few insertion elements and regions duplicated elsewhere in the genome. The only copies of an essential arg-tRNA gene and the minCDE genes are located on pSymB. Almost 20% of the pSymB sequence carries genes encoding solute uptake systems, most of which were of the ATP-binding cassette family. Many previously unsuspected genes involved in polysaccharide biosynthesis were identified and these, together with the two known distinct exopolysaccharide synthesis gene clusters, show that 14% of the pSymB sequence is dedicated to polysaccharide synthesis. Other recognizable gene clusters include many involved in catabolic activities such as protocatechuate utilization and phosphonate degradation. The functions of these genes are consistent with the notion that pSymB plays a major role in the saprophytic competence of the bacteria in the soil environment.

Bacterial Proteins↗
PubMed2001

Relaxed rrn expression and amino acid requirement of a Corynebacterium glutamicum rel mutant defective in (p)ppGpp metabolism.

The stringent response in Corynebacterium glutamicum was investigated. Sets of rrn-cat fusions were constructed in their native chromosomal position to examine the effects of amino acid starvation in a rel(+) strain and a Deltarel mutant defective in (p)ppGpp metabolism. The expression of the six rrn operons in the rel(+) control was stringently regulated and reduced to 79% upon induction of amino acid starvation. The Deltarel mutant displayed a relaxed regulation and was unable to reduce the rrn expression under amino acid depletion conditions. In addition, the Deltarel mutant grew more slowly in minimal medium than a rel(+) control. This growth effect was restored by a plasmid-encoded copy of rel or, alternatively, by supplementation of the minimal medium with the amino acid mixture casamino acids. In particular, the Deltarel strain of C. glutamicum displayed a requirement for the amino acids histidine and serine.

Amino Acids↗