Inoculation of sugarcane with Pantoea sp. increases amino acid contents in shoot tissues; serine, alanine, glutamine and asparagine permit concomitantly ammonium excretion and nitrogenase activity of the bacterium

Pantoea sp. is an endophytic nitrogen-fixing bacterium isolated from sugarcane tissues. The aim of the present study was to determine the contents of amino acids in sugarcane as a result of inoculation of nodes and nodal roots with Pantoea sp. strain 9C and to evaluate the effects of amino acids on growth, nitrogenase activity and ammonium excretion of the bacterium. Content of almost all amino acids increased in 30-day-old plantlets by root inoculation. The most abundant amino acids in shoot tissues were asparagine and proline, and those in nodal roots were asparagine, proline, aspartic acid, glutamic acid and serine. The bacterium was able to grow on all tested amino acids except histidine, isoleucine and leucine. Nitrogenase Pantoea sp. was partially inhibited by 1, 2 or 5mmolL(-1) and completely inhibited by 10mmolL(-1) of NH(4)(+) in the media. Pantoea sp. showed nitrogenase activity in 5mmolL(-1) of serine, asparagine, threonine, alanine, proline, tyrosine, valine, methionine, lysine, phenylalanine, cysteine, tryptophan, citrulline and ornithine. Pantoea sp. did not excrete ammonium when it grew in vivo conditions favoring nitrogen fixation; however, ammonium was detected in the supernatant when 5mmolL(-1) asparagine, aspartic acid, alanine, serine or glutamine was added to the medium. The highest ammonium concentration in the supernatant was detected, when Pantoea grew on serine. Ammonium in the supernatant and nitrogenase activity were only detectable concomitantly when the medium was supplemented with serine, alanine, glutamine or asparagine. We discuss roles of amino acids on plant-bacteria interaction during the colonization of sugarcane plants.

A putative new endophytic nitrogen-fixing bacterium Pantoea sp. from sugarcane

AIMS

To isolate and identify endophytic nitrogen-fixing bacteria in sugarcane growing in Cuba without chemical fertilizers.

METHODS AND RESULTS

Two N2-fixing isolates, 9C and T2, were obtained from surface-sterilized stems and roots, respectively, of sugarcane variety ML3-18. Both isolates showed acetylene reduction and H2 production in nitrogen-free media. Nitrogenase activity measured by H2 production was about 15 times higher for isolate 9C than for T2 or for Gluconoacetobacter diazotrophicus (PAL-5 standard strain, ATCC 49037). The nifH gene segment was amplified from both isolates using specific primers. Classification of both T2 and 9C was made on the basis of morphological, biochemical, PCR tests and 16S rDNA sequence analysis.

CONCLUSIONS

Isolate 9C was identified as a Pantoea species from its 16S rDNA, but showed considerable differences in physiological properties from previously reported species of this genus. For example, 9C can be cultured over a wide range of temperature, pH and salt concentration, and showed high H2 production (up to 67.7 nmol H2 h(-1) 10(10) cell(-1)). Isolate T2 was a strain of Gluconacetobacter diazotrophicus.

SIGNIFICANCE AND IMPACT OF THE STUDY

A new N2-fixing endophyte, i.e. Pantoea, able to produce H2 and to grow in a wide range of conditions, was isolated from sugarcane stem tissue and characterized. The strain with these attributes may well be valuable for agriculture.

Improved survival in steroid-refractory acute graft versus host disease after non-myeloablative allogeneic transplantation using a daclizumab-based strategy with comprehensive infection prophylaxis

Approximately 15% of patients undergoing non-myeloablative allogeneic haematopoietical cell transplantation (NMHCT) develop steroid-refractory acute-graft versus host disease (aGVHD), a usually fatal complication. We encountered 18 cases of steroid-refractory aGVHD in 146 patients, undergoing NMHCT from a related human leucocyte antigen-compatible donor following cyclophosphamide/fludarabine-based conditioning. Our initial cohort of steroid-refractory aGVHD patients treated with antithymocyte globulin (ATG) and mycophenolate mofetil (regimen-1: n = 6) had high GVHD-related mortality. Therefore, we investigated an alternative strategy for subsequent patients developing this complication (regimen-2: n = 12), consisting of daclizumab (alone or combined with infliximab/ATG) and targeted broad spectrum antibacterial and aspergillus prophylaxis in conjunction with rapid tapering of steroids to minimize opportunistic infections. In a retrospective analysis, patients receiving regimen-2 were significantly more likely to have complete resolution of GVHD compared with those receiving regimen-1 [12/12 (100%) vs. 1/6 (17%); P < 0.001]. When compared with those receiving regimen-1, regimen-2 patients also had a higher probability of survival at day 100 (100% vs. 50%) and day 200 (73% vs. 17%) post-transplant, and improved overall survival (median 453 d vs. 42 d from aGVHD onset; P < 0.0001). GVHD-related mortality was 89% for regimen-1 patients vs. 17% for regimen-2 patients (P < 0.0001). These data suggest that a co-ordinated approach using immunoregulatory monoclonal antibodies, pre-emptive antimicrobial therapy and judicious steroid withdrawal can dramatically improve outcome in steroid-refractory aGVHD.

Phase I Clinical Trial of Alitretinoin and Tamoxifen in Breast Cancer Patients: Toxicity, Pharmacokinetic, and Biomarker Evaluations

PURPOSE: To determine the overall and dose-limiting toxicities (DLTs) of alitretinoin (9-cis-retinoic acid) in combination with tamoxifen and the pharmacokinetics of alitretinoin alone and when combined with tamoxifen in patients with metastatic breast cancer. The effect of tamoxifen and alitretinoin on MIB-1, a marker of proliferation, in unaffected breast tissue was explored.

PATIENTS AND METHODS: Eligible patients had metastatic breast cancer. Previous tamoxifen therapy was allowed. Planned dose levels for alitretinoin ranged from 50 to 140 mg/m2/d with 20 mg/d tamoxifen in all patients after 4 weeks of alitretinoin as a single agent. Plasma concentrations of alitretinoin and retinol were measured at baseline and after 1, 2, and 3 months. Breast core biopsies were obtained at baseline and after 2 months of therapy.

RESULTS: Twelve patients with metastatic breast cancer received a total of 86 cycles of therapy. At 90 mg/m2/d, three of five patients experienced a DLT: grade 3 headache, grade 3 hypercalcemia, and grade 3 noncardiogenic pulmonary edema. At 70 mg/m2/d, one of six patients experienced a DLT (headache), and this level was considered the maximal tolerated dose in this study. Three toxicities occurred that had not been reported previously with alitretinoin: an asymptomatic delay in dark adaptation, a marked decrease in high-density lipoprotein cholesterol, and the occurrence of enthesopathy. Two of the nine assessable patients had a durable clinical response: one partial response and stable disease for 18 months and one complete response in continuous remission for 48+ months. Both responding patients were estrogen receptor–positive and had had previous tamoxifen therapy. There was a high degree of interpatient variability of plasma alitretinoin concentrations, although a significant decline in alitretinoin plasma levels over time was observed. MIB-1 scores declined in four of the eight paired breast specimens obtained.

CONCLUSION: The combination of tamoxifen and alitretinoin is well tolerated and has antitumor activity in metastatic breast cancer. The recommended phase II dose is 70 mg/m2/d with 20 mg/d tamoxifen.

Validation of a model of colon cancer progression

A unique feature of SW480 and SW620 colon carcinoma cell lines is that they are derived from primary and secondary tumours resected from a single patient. As such, they may represent a valuable resource for examining genetic changes late in colon cancer progression. In order to verify this, both cell lines have been characterized to determine whether phenotypic differences have been retained despite long-term cell culture in vitro. The primary tumour-derived SW480 cells have an epithelioid morphology in vitro, while metastasis-derived SW620 cells have a fibroblast-like appearance. Xenografts of SW480 cells form gland-like structures in vivo, while SW620 xenografts form solid sheets of tumour cells. SW620 cells have a higher BrdU labelling index than SW480 cells, and are more highly tumourigenic and metastatic. Furthermore, SW620 cells show less susceptibility to apoptosis induction by TNFalpha and anti-Fas monoclonal. Findings from these investigations therefore indicate that SW480 and SW620 cell lines do show appropriate phenotypic differences and represent an interesting model for studying the genetic events in the late stages of colon cancer progression.

Transcriptional analysis of major heat shock genes of Helicobacter pylori

The transcriptional organization and heat inducibility of the major heat shock genes hrcA, dnaK, dnaJ, groEL, and htpG were analyzed on the transcriptional level in Helicobacter pylori strain 69A. The strongly heat-induced dnaK operon was found to be tricistronic, consisting of the genes hrcA, grpE, and dnaK. The dnaJ gene specified one monocistronic mRNA which was also heat inducible. The genes groES and groEL were transcribed as one strongly heat-inducible bicistronic mRNA which exhibited exactly the same induction kinetic as the dnaK operon. Surprisingly, transcription of the monocistronic htpG gene was switched off after heat shock. The data presented are discussed with regard to the different mechanisms regulating expression of heat shock genes in H. pylori

Loss of heterozygosity in P53, BRCA1, and estrogen receptor genes and correlation to expression of p53 protein in ovarian epithelial tumors of different cell types and biological behavior

Loss of heterozygosity (LOH) of tumor suppressor genes (TSGs) in ovarian epithelial tumors of differing cell types and biological behavior has not been thoroughly investigated. Moreover, there have been conflicting reports correlating LOH of the p53 gene to overexpression of p53 protein. This study evaluated 34 formalin-fixed, paraffin-embedded ovarian epithelial tumors for LOH by polymerase chain reaction (PCR) for the following microsatellite markers: TP53(17p13.1/p53 gene), D17S579(17q/BRCA1 gene), and ESR (6q24-27/estrogen receptor gene). LOH of the TP53 marker was detected in 4 (44%) of 9 informative serous cystadenocarcinomas (SCa) but in 0 of 4 informative clear cell carcinomas (CCa) and 0 of 5 informative serous tumors of low malignant potential (SLMP). LOH of the BRCA1 marker was detected in 5 (83%) of 6 informative SCa, but in 1 (13%) of 8 informative CCa and 1 (14%) of 7 informative SLMP. LOH of the ESR marker was detected in 4 (50%) of 8 informative SCa, but in 0 of 4 informative CCa and 1 (16%) of 6 informative SLMP. p53 protein overexpression was present in 8 of 12 SCa but did not correlate to TP53 LOH. LOH for TP53, D17S579/ BRCA1, and ESR is common in ovarian SCa, and is observed in primary tumors as well as metastases. In contrast, these genetic alterations are less common in CCa and in the biologically less aggressive SLMP tumors. These data suggest different mechanisms of oncogenesis in ovarian epithelial tumors of different cell types and biological behavior.

Ammonium (methylammonium) transport by heterocysts and vegetative cells of Anabaena variabilis

Transport of the ammonium analogue [(14)C]methylammonium was similar in non-growing, fully differentiated heterocysts as compared to vegetative, multiplying cells of the filamentous cyanobacterium Anabaena variabilis. NH(4)(+) inhibited uptake into the cells and released accumulated methylammonium from the cells. These observations suggest that the main function of ammonium transport in heterocysts may not be NH(4)(+) acquisition but cyclic retention of ammonia produced by nitrogenase.

Characterization of the gltF gene product of Escherichia coli

The glt operon of Escherichia coli comprises the structural genes for the glutamate synthase subunits (gltB and gltD) and gltF, whose product was previously suggested to have regulatory functions. The A/T-rich region between gltD and gltF contains a weak promoter and a translation initiation site for gltF. The GltF protein is preceded by a signal peptide, which is cleaved off during export into the periplasmic space. A gltF::Km(R) insertion mutant was constructed and shown here to have no detectable phenotype with respect to amino acid utilization or ammonium transport. Thus, GltF is apparently not involved in regulation of nitrogen catabolism.

Long-term follow-up of chimpanzees inoculated with the first infectious clone for hepatitis C virus

Two chimpanzees (Ch1535 and Ch1536) became infected with hepatitis C virus (HCV) following intrahepatic inoculation with RNA transcribed from a full-length cDNA clone of the virus. Both animals were persistently infected and have been followed for 60 weeks. They showed similar responses to infection, with transient liver enzyme elevations and liver inflammatory responses, which peaked at weeks 17 (Ch1535) and 12 (Ch1536) postinoculation (p.i.). Antibody responses to structural and nonstructural proteins were first detected at weeks 13 (Ch1535) and 10 (Ch1536) p.i. Serum RNA titers increased steadily during the first 10 to 13 weeks but decreased sharply in both animals following antibody and inflammatory responses. Despite direct evidence of humoral immune responses to multiple viral antigens, including hypervariable region 1 (HVR1), both animals remained chronically infected. Detailed sequence analysis of serum HCV RNA revealed no change in the majority HVR1 sequence in Ch1535 and a single-amino-acid mutation in Ch1536, with very little clonal variation in either animal. Full-length genome analysis at week 60 revealed several amino acid substitutions localized to antigens E1, E2, p7, NS3, and NS5. Of these, 55.6 and 40% were present as the majority sequence in serum RNA isolated at week 26 p.i. (Ch1535) and week 22 p.i. (Ch1536), respectively, and could represent immune escape mutations. Mutations accumulated at a rate of 1.57 x 10(-3) and 1.48 x 10(-3) nucleotide substitutions/site/year for Ch1535 and Ch1536, respectively. Taken together, these data indicate that establishment of a persistent HCV infection in these chimpanzees is not due to changes in HVR1; however, the possibility remains that mutations arising in other parts of the genome contributed to this persistence.

Effect of inhibition of ornithine decarboxylase activity in a model of acute hepatocellular necrosis

OBJECTIVE

The effect of blockade of the enzyme ornithine decarboxylase by difluoromethylornithine (DFMO) on hepatocellular necrosis and survival in rats treated with thioacetamide (TAA) was investigated.

DESIGN

In one experiment, the effect of DFMO on survival of rats with TAA-induced acute hepatocellular necrosis was determined. In another experiment, blood and liver specimens were obtained from DFMO or saline-treated rats 24 h after the administration of TAA for determinations of serum alanine aminotransferase (ALT) and liver content of polyamines and microsomal cytochrome P-450 and for assessment of hepatic histology.

METHODS

Liver polyamines were determined by reversed-phase HPLC and microsomal cytochrome P-450 content by dithionite-difference spectroscopy of CO-treated homogenates. The severity of hepatocellular necrosis was scored blindly.

RESULTS

TAA-treated rats that received DFMO survived longer than saline-treated controls (P < 0.01). Serum ALT and liver putrescine concentrations were lower and the histological severity of acute hepatocellular necrosis was less in DFMO-treated rats with TAA-induced hepatocellular necrosis than in saline-treated controls (P < 0.05, P < 0.01 and P < 0.05, respectively). Total cytochrome P-450 levels were similar in DFMO and saline-treated rats with TAA-induced hepatocellular necrosis.

CONCLUSIONS

DFMO increases survival in TAA-induced fulminant hepatic failure by decreasing the severity of acute hepatocellular necrosis. The beneficial effects of DFMO do not appear to be mediated by its effects on polyamine metabolism, but may be attributable to an effect of DFMO on thioacetamide metabolism or on an alternative pathway of ornithine metabolism.

Ammonia-excreting mutants of Klebsiella pneumoniae with a pleiotropic defect in nitrogen metabolism

Enterobacterial mutants defective in the nitrogen control regulatory system (Ntr) generally display a pleiotropic phenotype with regard to expression and regulation of several enzymes and transport systems involved in the assimilation of N sources. This report describes the isolation and characterization of similar pleiotropic mutants of Klebsiella pneumoniae that cannot be complemented by ntr genes. The strains excreted ammonia, were unable to grow on a number of N sources, and contained low glutamine:2-oxoglutarate amino transferase and normal, but unmodifiable glutamine synthetase activities and a nitrogenase level largely unaffected by ammonium, but still repressible by an amino acid mixture. Genetic studies suggested that this phenotype is due to overexpression of an unknown regulatory protein.

Prolonged therapy of chronic hepatitis C with ribavirin

Therapy with ribavirin for 6-12 months is associated with decreases in serum aminotransferases in some patients with chronic hepatitis C. We have assessed the practicality and safety of prolonged therapy with ribavirin. Six patients with chronic hepatitis C were given 1000-1200 mg of ribavirin daily for 24 months. Serum aminotransferases and hepatitis C virus (HCV) RNA levels were monitored during and after therapy. Liver biopsies were carried out before and at the end of treatment. With therapy, mean serum alanine aminotransferase (ALT) levels fell from 161 U/L to 45 U/L at 12 months and to 39 U/L at 24 months. HCV RNA levels did not change. Liver histology improved in five and was unchanged in one patient. When therapy was stopped, aminotransferases rose to pretreatment levels. Side effects included mild fatigue and headaches. Two patients developed gallstones during therapy, perhaps caused by the chronic haemolysis that occurred in all patients. In conclusion, prolonged therapy with ribavirin can result in sustained improvements in serum aminotransferases and hepatic histology in a proportion of patients with chronic hepatitis C. Ribavirin therapy does not cause decreases in viraemia and, therefore, probably must be continued indefinitely to provide lasting benefit. The advantages of such therapy must be weighed against possible long-term side-effects.

Hepatic failure and lactic acidosis due to fialuridine (FIAU), an investigational nucleoside analogue for chronic hepatitis B

BACKGROUND

We describe severe and unexpected multisystem toxicity that occurred during a study of the antiviral nucleoside analogue fialuridine (1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil, or FIAU) as therapy for chronic hepatitis B virus infection.

METHODS

Fifteen patients with chronic hepatitis B were randomly assigned to receive fialuridine at a dose of either 0.10 or 0.25 mg per kilogram of body weight per day for 24 weeks and were monitored every 1 to 2 weeks by means of a physical examination, blood tests, and testing for hepatitis B virus markers.

RESULTS

During the 13th week lactic acidosis and liver failure suddenly developed in one patient. The study was terminated on an emergency basis, and all treatment with fialuridine was discontinued. Seven patients were found to have severe hepatotoxicity, with progressive lactic acidosis, worsening jaundice, and deteriorating hepatic synthetic function despite the discontinuation of fialuridine. Three other patients had mild hepatotoxicity. Several patients also had pancreatitis, neuropathy, or myopathy. Of the seven patients with severe hepatotoxicity, five died and two survived after liver transplantation. Histologic analysis of liver tissue revealed marked accumulation of microvesicular and macrovesicular fat, with minimal necrosis of hepatocytes or architectural changes. Electron microscopy showed abnormal mitochondria and the accumulation of fat in hepatocytes.

CONCLUSIONS

In patients with chronic hepatitis B, treatment with fialuridine induced a severe toxic reaction characterized by hepatic failure, lactic acidosis, pancreatitis, neuropathy, and myopathy. This toxic reaction was probably caused by widespread mitochondrial damage and may occur infrequently with other nucleoside analogues.

Function of hisF and hisH gene products in histidine biosynthesis

A mutant of the enterobacterium Klebsiella pneumoniae with a defect in the hisF gene (in the histidine biosynthesis pathway) was isolated, which can only grow with high but not low ammonia concentrations. The mutated hisF product can use ammonia for the formation of the imidazole ring of histidine but not glutamine provided by the hisH product. Site-directed insertional mutagenesis of hisH led to the same dependence of prototrophic growth on high ammonia levels. The nucleotide sequence of K. pneumoniae hisF is almost identical to that of hisF from other enterobacteria. Similarities of the hisF product with the hisA product and of HisH sequences with the glutamine binding domains of TrpG-type amidotransferases provide additional evidence for the functions of the hisF and hisH products in histidine biosynthesis, namely that HisF catalyzes the ammonolytic cleavage of N'-(5'-phosphoribulosyl)-formimino-5- aminoimidazole-4-carboxamide ribonucleotide either utilizing free ammonia or deriving the ammonia moiety from glutamine bound to HisH.

[Sequelae of cannabis use--results of a survey of experts on traffic accidents and "echopsychoses" (flash-back)]

There is a lack of knowledge in the judgement of the effects and the dangerousness of cannabis. Specially in the judgement of the delinquency of traffic the effects must be clarified. Cannabis plays often a fundamental role in road accidents. Obviously flash-backs of consumers of cannabis are observed more often than documented in the literature hitherto. The existing but not published experiences of experts have to be considered extensively to get an idea more complete of the diverse effects of cannabis in traffic offences.

Genetic analysis of the regulatory putP region (coding for proline permease) in Klebsiella pneumoniae M5a1: evidence for regulation by the nac system

During a search for nitrogen-controlled promoters on the Klebsiella pneumoniae M5a1 chromosome, the regulatory region of putP (coding for proline permease) was cloned, sequenced and analyzed. The region contained a weak sigma 70-dependent promoter and putative binding sites for the cAMP-CAP complex and the Nac regulatory protein, the latter probably providing a link with the nitrogen regulation (Ntr) system. Using a lacZ gene fusion, evidence for control of putP transcription by both Nac and Ntr was obtained.

Fazarabine: a report of response in a patient with multiply relapsed embryonal cell carcinoma

This report describes a patient with multiply relapsed and advanced metastatic embryonal cell carcinoma who achieved a pathological partial remission (PR) following treatment with a Phase I chemotherapeutic agent, arabinosyl-5-azacytosine (Ara-AC), followed by orchiectomy. The antimetabolic Ara-AC is worthy of further study in patients with germ-cell tumors. It would appear that the antimetabolite Ara-AC may have significant activity in patients with germ-cell tumors.

High plasma clozapine levels in tardive dyskinesia

Studies in the literature that attempt to relate neuroleptic plasma levels to the development of tardive dyskinesia (TD) report inconsistent findings. As part of an open, long-term study, 60 schizophrenic and schizoaffective patients were started gradually on a b.i.d. schedule of the atypical antipsychotic drug clozapine. Blood samples were drawn weekly for 6 weeks and analyzed for a variety of constituents including clozapine plasma levels. Patients with higher levels of TD were found to have significantly higher levels of plasma clozapine and a higher ratio of plasma/dose than those with lower levels of TD. Our data suggests that schizophrenics with TD may have different pharmacokinetics, drug metabolism, and elimination processes than those without TD. Higher typical plasma neuroleptic levels may increase susceptibility to TD development. A second hypothesis implies that it is not the higher mean plasma level of a neuroleptic that is associated with TD but the greater fluctuations of plasma levels over time (i.e., a higher variance). This hypothesis is discussed in the context of our data.

The gltF gene of Klebsiella pneumoniae: cloning and initial characterization

From a gene bank of Klebsiella pneumoniae M5a1, a 1.7 kb gene fragment was isolated which was able to restore the Ntr+ phenotype and ammonium (methylammonium) transport, but not glutamate synthase in an Escherichia coli glt mutant (glutamate synthase deficiency). The fragment strongly hybridized with the gltF regulatory gene from E. coli. After subcloning the fragment into an overexpression vector, a protein with a molecular weight of 27,000 dalton was identified as the gene product. The results indicate that the fragment cloned contains the gltF gene from K.pneumoniae.

Dismutation of hydroxylamine to ammonia and nitrite by a novel, membrane-bound enzyme from the cyanobacterium Phormidium uncinatum

Extracts from ammonium-grown phototrophic cultures of Phormidium uncinatum exhibited a catalytic and stoichiometric formation of nitrite and ammonia from hydrogen peroxide and hydroxylamine. This reaction was due to a novel enzyme (referred to as hydroxylamine dismutase), which was bound to the heavier thylakoid membranes. The enzyme was solubilized from the membranes by detergent treatment and further purified by ion-exchange chromatography. On the basis of inhibitor studies, the involvement of metal ions and sulfhydryl groups in the characteristic reaction is suggested.

Assimilation of methylamine by Paracoccus denitrificans involves formaldehyde transport by a specific carrier

Assimilation of methylamine by Paracoccus denitrificans involves the following enzymes: a periplasmic methylamine dehydrogenase, a formaldehyde transport system, cytoplasmic formaldehyde and formate dehydrogenase. Formaldehyde transport follows saturation kinetics with a high substrate affinity (Km = 7 microM), and is severely inhibited by iodoacetate, cyanide and p-trifluoromethoxy carbonylcyanide phenylhydrazone. Expression of the formaldehyde carrier is regulated by the carbon source.

Construction of multicopy expression vectors for regulated over-production of proteins in Klebsiella pneumoniae and other enteric bacteria

A number of expression vectors have been constructed to allow over-production of selected gene products in Klebsiella pneumoniae and other enteric bacteria. The plasmids use the strong hybrid trp-lac (tac) promoter for gene expression, which is regulated by the lacIQ allele of the lac repressor carried on the vector. This provides very tight regulation of gene expression, which is important for over-production of proteins which may be detrimental to cell growth. The vectors carry the standard mp18 cloning nest in which all the restriction sites are unique to the plasmid (with the exception of EcoRI in pDK7). Derivatives were constructed carrying kanamycin, chloramphenicol or ampicillin resistance as selectable markers, the first two of which are advantageous in K. pneumoniae due to the high inherent beta-lactamase activity of this organism.

N2 fixation and NH4+ assimilation in the thermophilic anaerobes Clostridium thermosaccharolyticum and Clostridium thermoautotrophicum

Inorganic nitrogen metabolism in the obligate anaerobic thermophiles Chlostridium thermosaccharolyticum and Clostridium thermoautotrophicum differs in several respects. C. thermosaccharolyticum contains a nitrogenase as inferred from NH4+ repressible C2H2 reduction, a glutamine synthetase which is partially repressed by ammonium, very labile glutamate synthase activities with both NADH and NADPH, NADPH-dependent glutamate dehydrogenase, and NH4+-dependent asparagine synthetase. C. thermoautotrophicum contains no nitrogenase, but glutamine synthetase, no glutamate synthase, no glutamate dehydrogenase, but a NADH-dependent alanine dehydrogenase and a NH4+-dependent asparagine synthetase.

Energy expenditure for cyclic retention of NH3/NH4+ during N2 fixation by Klebsiella pneumoniae

The permeability coefficient for NH3 through bacterial membranes was determined to be around 2 X 10(-3) cm X s-1. This value was used to calculate the outward diffusion of NH3 from intracellular pools and the energy costs for reabsorption as NH4+. For an N2-fixing continuous culture of Klebsiella pneumoniae an energy expenditure of around 4 ATP per NH3 produced was calculated, thus increasing significantly the energy requirement for N2 fixation in vivo.

Some properties of a Klebsiella pneumoniae ammonium transport negative mutant (Amt-)

The main property of an Amt- (ammonium transport negative) mutant of Klebsiella pneumoniae is its inability to accumulate NH4+ intracellularly. When growing on nitrogen sources other than NH4+, the mutant constantly looses NH3 by diffusion. This loss results in poor growth. The NH3 excretion suggests the existence of a futile cycle (NH3 loss/NH4+ reabsorption) in the wild type and possibly other bacterial strains, which do not constantly excrete NH3.

Uptake of methionine sulfoximine by some N2 fixing bacteria, and its effect on ammonium transport

The N2 fixing bacteria Klebsiella pneumoniae, Azospirillum brasilense, Rhodopseudomonas sphaeroides and Rhodospirillum rubrum, but not Azotobacter vinelandii accumulate the glutamine analogue methionine sulfoximine in the cell. In the accumulating cells methionine sulfoximine inhibits ammonium transport. Accumulation and inhibition are prevented by glutamine.

Ammonium (methylammonium) transport by Klebsiella pneumoniae

Klebsiella pneumoniae can accumulate methylammonium up to 80-fold by means of a transport system as indicated by the energy requirement, saturation kinetics and a narrow pH profile around pH 6.8. Methylammonium transport (apparent Km = 100 microM, V = 40 mumol/min per g dry weight at 15 degrees C) is competitively inhibited by ammonium (apparent Ki = 7 microM). The low Ki value and the finding that methylammonium cannot serve as a nitrogen source indicate that ammonium rather than methylammonium is the natural substrate. Uphill transport is driven by a component of the protonmotive force, probably the membrane potential. The transport system is under genetic control; it is partially repressed by amino acids and completely by ammonium. Analysis of mutants suggest that the synthesis of the ammonium transport system is subject to the same 'nitrogen control' as nitrogenase and glutamine synthetase.

Some properties of a new electrogenic transport system: the ammonium (methylammonium) carrier from Clostridium pasteurianum

Clostridium pasteurianum is able to build up about 100-fold gradients of methylammonium across the cell membrane. Methylammonium enters the cell by means of a carrier as shown by the energy requirement, saturation kinetics and a pH profile with a narrow maximum between pH 6.2 and 6.8. The methyl ammonium transport (apparent Km = 150 microM, V = 100 mumol/min per g dry weight) is competitively inhibited by ammonium (apparent Ki = 9 microM). The low Ki value and the observation that methylammonium cannot serve as a carbon or nitrogen source for Cl. pasteurianum strongly indicate that ammonium rather than methylammonium is the natural substrate. Uncouplers and inhibitors of energy metabolism or of the membrane-bound ATPase inhibit transport. Cl. pasteurianum maintains a membrane potential (interior negative) in the range 80-130 mV. This membrane potential was identified as the energy source: the same agents that block transport also decrease the membrane potential, and artificial generation of a membrane potential (by addition of valinomycin to K+-loaded cells) induces concentrative uptake of methylammonium. Thus NH4+ (or CH3NH3+) must be the transported species. Digestion of the cell wall by lysozyme does not abolish the transport activity.