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At least 991 records · Page 55Linked to original sources
PubMed1970

Nucleic acid homologies among oxidase-negative Moraxella species.

The deoxyribonucleic acid (DNA) base composition and DNA homologies of more than 40 strains of oxidase-negative Moraxella species were determined. These bacteria have also been identified as belonging to the Mima-Herellea-Acinetobacter group and the Bacterium anitratum group, as well as to several other genera including Achromobacter and Alcaligenes. The DNA base content of these strains ranged from 40 to 46% guanine plus cytosine. DNA-DNA competition experiments distinguished five groups whose members were determined by showing 50% or more homology to one of the reference strains: B. anitratum type B5W, Achromobacter haemolyticus var. haemolyticus, Alcaligenes haemolysans, Achromobacter metalcaligenes, and Moraxella lwoffi. A sixth group comprised those strains showing less than 50% homology to any of the reference strains. Negligible homology was found between strains of oxidase-negative and oxidase-positive Moraxella species in DNA-DNA competition experiments. However, evidence of a distant relationship between the two groups was obtained in competition experiments by using ribosomal ribonucleic acid.

Bacteria↗
PubMed1970

Elimination of sex factors in Escherichia coli by urea.

Eliminatory action of urea on the sex factor (F) in Escherichia coli K-12 strains is reported. Growth of E. coli harboring F or F'8 (F-gal) factors in Penassay Broth containing urea led to the loss of these genetic elements and yielded F(-) cells. Appearance of F(-) cells among survivors was already observed when the culture was in the very early stage of exponential phase. However, frequencies of F(-) cells formed did not increase much as a function of the incubation time. Unusual F(+) or F'8 cells which retained the ability of genetic transfer but showed resistance to M12 phage were also isolated. Addition of sucrose to broth with urea led to the favorable growth of cells in the culture and the increase, if little, of elimination frequencies of F factors by urea. These findings, coupled with other observations, suggest that urea has two separate actions in enhancing the frequency of F(-) bacteria, namely, (i) to inactivate F by direct action, such as mutation, and (ii) to select the F(-) variants by differentially inhibiting the growth of F(+).

Bacteriological Techniques↗
PubMed1971

Mechanism of D-cycloserine action: transport mutants for D-alanine, D-cycloserine, and glycine.

The accumulation of d-alanine and the accumulation of glycine in Escherichia coli are related and appear to be separate from the transport of l-alanine. The analysis of four d-cycloserine-resistant mutants provides additional support for this conclusion. The first-step mutant from E. coli K-12 that is resistant to d-cycloserine was characterized by the loss of the high-affinity line segment of the d-alanine-glycine transport system in the Lineweaver-Burk plot. This mutation, which is linked to the met(1) locus, also resulted in the loss of the ability to transport d-cycloserine. The second-step mutation that is located 0.5 min from the first-step mutation resulted in the loss of the low-affinity line segment for the d-alanine-glycine transport system. The transport of l-alanine was decreased only 20 to 30% in each of these mutants. A multistep mutant from E. coli W that is 80-fold resistant to d-cycloserine lost >90% of the transport activity for d-alanine and glycine, whereas 75% of the transport activity for l-alanine was retained. E. coli W could utilize either d- or l-alanine as a carbon source, whereas the multistep mutant could only utilize l-alanine. Thus, a functioning transport system for d-alanine and glycine is required for both d-cycloserine action and growth on d-alanine.

Alanine↗
PubMed1971

Involvement of recombination genes in growth and viability of Escherichia coli K-12.

We have studied the growth properties of 17 isogenic strains of Escherichia coli K-12 differing only in the recA, recB, recC, and sbcA alleles. We have observed the following. (i) All recombination deficient strains have decreased growth rates and decreased viabilities compared with recombination proficient strains. The large populations of nonviable cells in Rec(-) cultures may arise by spontaneous lethal sectoring (9). (ii) A recA mutant strain which is entirely recombination deficient and which shows high ultraviolet sensitivity and "reckless" deoxyribonucleic acid (DNA) breakdown has approximately the same growth rate and twice the viability as recB and recC mutant strains which have residual recombination proficiency, moderate ultraviolet sensitivity, and "cautious" DNA breakdown. (iii) Indirectly suppressed (sbcA(-)) recombination proficient (Rec(+)) revertants of recB and recC mutant strains have approximately normal growth rates and are three times as viable as their Rec(-) ancestors (but not as viable as rec(+) cells). We suggest the following hypothesis to account for the low viability of Rec(-)E. coli. Single-strand breaks in the DNA duplex, necessary for normal bacterial growth, may be repaired in a Rec(+) cell. Failure of Rec(-) cells to repair this normal DNA damage may lead to the observed loss of viability.

Bacterial Proteins↗
PubMed1971

Inefficiency of genetic recombination in hybrids between Escherichia coli and Salmonella typhosa.

An Escherichia coli Hfr strain in which three negative chromosomal alleles (leu(-), arg(-), and mtl(-)) were closely linked to three positive alleles (ara(+), rha(+), and xyl(+), respectively) was employed in matings with a Salmonella typhosa recipient. The detected expression of the negative E. coli alleles in S. typhosa hybrids selected for receipt of an associated positive E. coli marker was used to determine the occurrence of haploid S. typhosa recombinants, as distinguished from stable partial diploid hybrids. At the same time, the inheritance patterns and segregation behavior of the positive alleles provided indicators of the occurrence of partial diploid hybrids. Examination of both positive and negative markers inherited by ara(+), rha(+), and xyl(-) selected S. typhosa hybrid classes indicated that relatively short E. coli chromosomal segments (generally about 4 min or less in length) were involved in recombination (haploidy), whereas rather extensive E. coli genetic segments were conserved in the diploid state. S. typhosa hybrids selected for receipt of the ara(+) marker showed a 52% incidence of leu(-) haploidy, which is probably close to being an accurate measure of recombination at the site of the ara(+) allele. S. typhosa hybrids selected for receipt of the rha(+) or xyl(+) markers showed only a 20% incidence of arg(-) or mtl(-) haploidy, respectively, but both of these hybrid classes exhibited a higher incidence of conservation of extensive E. coli diploid segments than did the ara(+) selected class. Remating of haploid S. typhosa hybrids with recombinant xyl(+)mtl(-) or rha(+)arg(-) regions resulted in higher frequencies of hybrid recovery than were observed in the initial matings. However, there was a higher incidence of partial diploidy and a lower incidence of haploidy among the hybrids obtained from these rematings.

Alleles↗
PubMed1971

Biochemical bases for the antimetabolite action of L-serine hydroxamate.

The amino acid analogue l-serine hydroxamate, which is bacteriostatic for Escherichia coli, has been shown to inhibit protein synthesis. The antimetabolite is a competitive inhibitor of seryl-transfer ribonucleic acid (tRNA) synthetase with a K(i) value of 30 mum. Mutants resistant to l-serine hydroxamate have been selected, and three were shown to have seryl-tRNA synthetases with increased K(i) values. One mutant contains a 3-phosphoglycerate dehydrogenase which is insensitive to inhibition by l-serine.

Bacterial Proteins↗
PubMed1971

Precursor ribosomal ribonucleic acid and ribosome accumulation in vivo during the recovery of Salmonella typhimurium from thermal injury.

When cells of S. typhimurium were heated at 48 C for 30 min in phosphate buffer (pH 6.0), they became sensitive to Levine Eosin Methylene Blue Agar containing 2% NaCl (EMB-NaCl). The inoculation of injured cells into fresh growth medium supported the return of their normal tolerance to EMB-NaCl within 6 hr. The fractionation of ribosomal ribonucleic acid (rRNA) from unheated and heat-injured cells by polyacrylamide gel electrophoresis demonstrated that after injury the 16S RNA species was totally degraded and the 23S RNA was partially degraded. Sucrose gradient analysis demonstrated that after injury the 30S ribosomal subunit was totally destroyed and the sedimentation coefficient of the 50S particle was decreased to 47S. During the recovery of cells from thermal injury, four species of rRNA accumulated which were demonstrated to have the following sedimentation coefficients: 16, 17, 23, and 24S. Under identical recovery conditions, 22, 26, and 28S precursors of the 30S ribosomal subunit and 31 and 48S precursors of the 50S ribosomal subunit accumulated along with both the 30 and 50S mature particles. The addition of chloramphenicol to the recovery medium inhibited both the maturation of 17S RNA and the production of mature 30S ribosomal subunits, but permitted the accumulation of a single 22S precursor particle. Chloramphenicol did not affect either the maturation of 24S RNA or the mechanism of formation of 50S ribosomal subunits during recovery. Very little old ribosomal protein was associated with the new rRNA synthesized during recovery. New ribosomal proteins were synthesized during recovery and they were found associated with the new rRNA in ribosomal particles. The rate-limiting step in the recovery of S. typhimurium from thermal injury was in the maturation of the newly synthesized rRNA.

Bacterial Proteins↗
PubMed1971

Mutants of Escherichia coli sensitive to antibiotics.

Mutants of Escherichia coli sensitive to the antibiotic synergistin A, an inhibitor of protein synthesis, were isolated. These mutants were pleiotropic, being also sensitive to a large number of unrelated antibiotics and to lysis by detergents. These pleiotropic responses indicated that the mutations affected cell wall or membrane synthesis. Consequently, selection for antibiotic-sensitive mutants constitutes a useful means for isolating cell wall or membrane mutants.

Anti-Bacterial Agents↗
PubMed1971

Identification of the forms of vitamin B 6 present in the culture media of "vitamin B 6 control" mutants.

An Escherichia coli mutant resistant to isoniazid (WG497) contained 0.6 mumole of extracellular pyridoxamine and pyridoxamine phosphate in the early stationary phase. A suppressed lysine mutant (AT1024) contained 1.4 mumoles of pyridoxal phosphate under the same conditions. The internal concentration of vitamin B(6) was one-half of normal for AT1024 and increased fivefold for WG497.

Biological Assay↗
PubMed1971

Lethal synthesis of methylglyoxal by Escherichia coli during unregulated glycerol metabolism.

In Escherichia coli K-12, the conversion of glycerol to triose phosphate is regulated by two types of control mechanism: the rate of synthesis of glycerol kinase and the feedback inhibition of its activity by fructose-1,6-diphosphate. A strain which has lost both control mechanisms by successive mutations, resulting in the constitutive synthesis of a glycerol kinase no longer sensitive to feedback inhibition, can produce a bactericidal factor from glycerol. This toxic factor has been identified by chemical and enzymological tests as methylglyoxal. Methylglyoxal can be derived from dihydroxyacetone phosphate through the action of an enzyme which is present at high constitutive levels in the extracts of the mutant as well as that of the wild-type strain. Nine spontaneous mutants resistant to 1 mm exogenous methylglyoxal have been isolated. In all cases the resistance is associated with increased levels of a glutathione-dependent enzymatic activity for the removal of methylglyoxal. Methylglyoxal-resistant mutants derived from the glycerol-sensitive parental strain also became immune to glycerol.

Aldehydes↗
PubMed1971

Nystatin-resistant mutants of yeast: alterations in sterol content.

Mutants of the genes nys1 and nys3 differ from sensitive strains (nys(+)) in their sterol content. Ultraviolet absorption spectra of the nonsaponifiable material extracted from cells of nys(+) demonstrated the presence of ergosterol and 24(28)-dehydroergosterol. In nys1 mutants, the spectrum suggests the presence of a new sterol. The absorption spectrum of extracts from nys3 mutants indicates absence of both ergosterol and 24(28)-dehydroergosterol and presence of another new sterol. Conversion of nys(+) and nys3 to petite results in loss of 24(28)-dehydroergosterol in the former and the new sterol in the latter, whereas the new sterol in nys1 is only reduced. The sterols in ethanol-grown cells of all genotypes are essentially the same as is found for growth on glucose. With the exception of nys3 grown on ethanol, the mutants do not appear to be at a disadvantage compared to wild type.

Alkanes↗