Rhizobium sp. strain ORS571 grows synergistically on N2 and nicotinate as N sources.

Rhizobium sp. strain ORS571 conducts synergistic, free-living N2 fixation and nicotinate oxidation. Explicitly, ORS571 is able to fix N2 aerobically because 6-OH-nicotinate acts as an intracellular O2 sink. Because 6-OH-nicotinate oxidation is mandatory for aerobic, free-living N2 fixation and because the synergistic processes yield ammonium from substrates (as the nitrogen source for growth), ORS571 is not a diazotroph.     

What are mycoplasmas: The relationship of tempo and mode in bacterial evolution

Summary In phenotype the mycoplasmas are very different from ordinary bacteria. However, genotypically (i.e., phylogenetically) they are not. On the basis of ribosomal RNA homologies the mycoplasmas belong with the clostridia, and indeed havespecific clostridial relatives. Mycoplasmas are, however, unlike almost all other bacteria in the evolutionary characteristics of their ribosomal RNAs. These RNAs contain relatively few of the highly conserved oligonucleotide sequences characteristic of normal eubacterial ribosomal RNAs. This is interpreted to be a reflection of an elevated mutation rate in mycoplasma lines of descent. A general consequence of this would be that the variation associated with a mycoplasma population is augmented both in number and kind, which in turn would lead to an unusual evolutionary course, one unique in all respects. Mycoplasmas, then, are actually tachytelic bacteria. The unusual evolutionary characteristics of their ribosomal RNAs are the imprints of their rapid evolution.     

Mismatch Repair Mutations of ESCHERICHIA COLI K12 Enhance Transposon Excision

Excision of the prokaryotic transposon Tn10 is a host-mediated process that occurs in the absence of recA function or any transposon-encoded functions. To determine which host functions might play a role in transposon excision, we have isolated 40 mutants of E. coli K12, designated tex, which increase the frequency of Tn10 precise excision. Three of these mutations (texA) have been shown to qualitatively alter RecBC function. We show that 21 additional tex mutations with a mutator phenotype map to five genes previously identified as components of a methylation-directed pathway for repair of base pair mismatches: uvrD, mutH, mutL, mutS and dam. Previously identified alleles of these genes also have a Tex phenotype.--Several other E. coli mutations affecting related functions have been analyzed for their effects on Tn10 excision. Other mutations affecting the frequency of spontaneous mutations (mutT, polA, ung), different excision repair pathways (uvrA, uvrB) or the state of DNA methylation (dcm) have no effect on Tn10 excision. Mutations ssb-113 and mutD5, however, do increase Tn10 excision.--The products of the mismatch correction genes probably function in a coordinated way during DNA repair in vivo. Thus, mutations in these genes might also enhance transposon excision by a single general mechanism. Alternatively, since mutations in each gene have qualitatively and quantitatively different effects on transposon excision, defects in different mismatch repair genes may enhance excision by different mechanisms.     

Temporal Profiles of Proteins Responsive to Transient Ischemia

The responses of long and short half-lived proteins to ischemia were measured in rat brain during 6 days of recovery from 30 min of transient forebrain ischemia produced by four-vessel occlusion. At the end of the ischemic interval, the neocortical activities of four vulnerable enzymes [ornithine (ODC) and S-adenosylmethionine (SAMDC) decarboxylases, and RNA polymerases I and II] were unchanged, but within 30 min of reperfusion, their activities dropped by 25-50%. The loss of substance P in the striatum and substantia nigra was slower, reaching about 50% by 12 h. On the other hand, the activities of 5 long half-lived enzymes did not change in the neocortex at 5 and 15 h of reperfusion and regional protein concentrations were essentially unaffected over 6 days survival. The rate and extent of normalization of the amounts or activities of the vulnerable proteins varied. RNA polymerase II and ODC activities were restored within 4 h, and ODC showed a biphasic increase in activity, with peaks at 10 h and 2-3 days. RNA polymerase I and SAMDC activities were restored by 18 h and 5 days, respectively, whereas substance P concentrations did not completely recover, even at 6-15 days. The greater the regional reduction of blood flow during ischemia, the larger the net change (gain or loss) of SAMDC or ODC activity and the longer the time required to normalize the activities of these enzymes. The average rate of proteolysis, assessed by measuring the rate of clearance of 14C from protein prelabeled with [14C]bicarbonate, was abnormal during the first 2 days of reperfusion. Postischemic changes in both protein synthesis and degradation could affect the amounts of some of the proteins responsive to transient ischemia.     

Inhibition of a Low Km GTPase Activity in Rat Striatum by Calmodulin

In rat striatum, the activation of adenylate cyclase by the endogenous Ca2+-binding protein, calmodulin, is additive with that of GTP but is not additive with that of the nonhydrolyzable GTP analog, guanosine-5'-(beta, gamma-imido)triphosphate (GppNHp). One possible mechanism for this difference could be an effect of calmodulin on GTPase activity which has been demonstrated to "turn-off" adenylate cyclase activity. We examined the effects of Ca2+ and calmodulin on GTPase activity in EGTA-washed rat striatal particulate fractions depleted of Ca2+ and calmodulin. Calmodulin inhibited GTP hydrolysis at concentrations of 10(-9)-10(-6) M but had no effect on the hydrolysis of 10(-5) and 10(-6) M GTP, suggesting that calmodulin inhibited a low Km GTPase activity. The inhibition of GTPase activity by calmodulin was Ca2+-dependent and was maximal at 0.12 microM free Ca2+. Maximal inhibition by calmodulin was 40% in the presence of 10(-7) M GTP. The IC50 for calmodulin was 100 nM. In five tissues tested, calmodulin inhibited GTP hydrolysis only in those tissues where it could also activate adenylate cyclase. Calmodulin could affect the activation of adenylate cyclase by GTP in the presence of 3,4-dihydroxyphenylethylamine (DA, dopamine). Calmodulin decreased by nearly 10-fold the concentration of GTP required to provide maximal stimulation of adenylate cyclase activity by DA in the striatal membranes. The characteristics of the effect of calmodulin on GTPase activity with respect to Ca2+ and calmodulin dependence and tissue specificity parallel those of the activation of adenylate cyclase by calmodulin, suggesting that the two activities are closely related.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation between limitation of growth ofPachysolen tannophilus on D-xylose with the formation of ethanol and other products

The formation of ethanol, xylitol, ribitol, arabitol and acetic acid from D-xylose byPachysolen tannophilus correlated with the limitation of growth. The correlation was consistent with these products being secondary metabolites.Issued as NRCC Publication Number 24259.     

Effect of slow feeding of xylose on ethanol yield byPachysolen tannophilus

Summary With slow feeding of xylose to a batch fermentation byPachysolen tannophilus, the yield of ethanol from xylose was improved to 0.41 g/g (80% of theoretical) with a maximum ethanol concentration of 26.5 g/L at 120 h. This is a 41% improvement on the ethanol yield observed for batch fermentations without slow feeding. The optimum level of xylose in the medium was determined to be between 5 and 8g/L; xylose at greater than 10 g/L leads to xylitol accumulation, whereas xylose below 3 g/L permits ethanol to be oxidized to acetate. This latter effect is exacerbated by increased aeration.     

Molecular analysis of gene deletion in aniridia-Wilms tumor association

Summary Hybrid clones were produced from the fusion of Chinese hamster cells and human fibroblasts from a patient with the aniridia-Wilms tumor association (AWTA). The DNA from the parental cells and the hybrid clones was screened by Southern blot and DNA hybridization with probes for the human insulin and Ha-ras-1 genes. Two alleles for the Ha-ras-1 gene were shown to exist in the AWTA cells by restriction fragment length polymorphism. One hybrid clone, containing a single allele for Ha-ras-1 was shown to contain a single chromosome 11 with a cytogenetically visible deletion at 11p13. The DNA from this hybrid contained the human genes for insulin, ^A, ^G, Ha-ras-1, and calcitonin, but lacked any human sequences homologous to a human catalase cDNA. This clone was also shown to express human lactate dehydrogenase A (LDH A) activity. These data indicate that the deletion of the affected chromosome in this AWTA patient begins distal to LDH A and includes band 11p13, but does not extend to calcitonin or other genes thought to be located in the distal half of chromosome 11p.     

Rhizobium sp. strain ORS571 ammonium assimilation and nitrogen fixation.

Among rhizobia studied, Rhizobium sp. strain ORS571 alone grew unambiguously on N2 as sole N source. In ORS571 , only the glutamine synthetase (GS)-glutamate synthase ( GOGAT ) pathway assimilated ammonium. However, ORS571 exhibited two unique physiological aspects of this pathway: ORS571 had only GS I, whereas all other Rhizobiaceae studied had both GS I and GS II, and both NADPH- and NADH-dependent GOGAT activities were present. ORS571 GS-affected and NADPH- GOGAT -affected mutant strains were defective in both ammonium assimilation (Asm-) and N2 fixation (Nif-) in culture and in planta ; NADH- GOGAT mutants were Asm- but Nif+. "Bacteroid" GS activity was essentially nil, suggesting symbiotic ammonium export. Physiological studies on effects of glutamine, ammonium, methionine sulfoximine, and diazo-oxo-norleucine on nitrogenase induction in culture implied a regulatory role for the intracellular glutamine pool.     

The response of stream macroinvertebrates to substrate size and heterogeneity

Manipulations of substrate size and components of heterogeneity were designed to test their independent effects and interactions on the abundance and species richness of stream macroinvertebrates. Two components of substrate heterogeneity, variation in size class proportions and number of size classes, had no independent effect on abundance or richness; and in general did not interact with median particle size. Median particle size, stream current, and detritus accounted for most of the significant variation in macroinvertebrates colonizing the experimental substrates. Rocks with high surface heterogeneity (roughness) were colonized by more individuals (but not taxa) than rocks with low surface heterogeneity.