Autolytic activity associated with competent group H streptococci

Competent cells of group H streptococci strains Wicky and Challis autolyzed markedly when placed at 37 C in 0.05 m tris(hydroxymethyl)methyl-amino-propane sulfonic acid buffer (pH 9.0 to 9.1) containing 0.02 m 2-mercaptoethanol, whereas noncompetent cells autolyzed slightly. Autolysis of competent Wicky cells did not occur at 0 C or after the cells were heated at 100 C for 5 min. Culture fluids derived from strain Challis that contained competence factor (CF) activity did not contain lytic activity. Addition of native deoxyribonucleic acid (DNA) to competent Wicky cells caused a retardation in the rate of autolysis; ribonucleic acid and alkali-denatured DNA had less of an effect. Supernantant fluids derived from competent cell lysates lysed noncompetent Wicky cells but were inactive against cells of Hydrogenomonas eutropha, a group A Streptococcus, and against a commercial lysozyme substrate (Micrococcus lysodeikticus). This lytic activity was inactivated by heat (5 min at 100 C). Electron microscopic observations of autolyzed cells showed that autolysis occurs only at the site of cross-wall formation. A close relationship between the development of competence and autolysis is suggested by the fact that certain conditions that prevent the establishment of the competent state in Wicky populations (such as no CF, addition of CF simultaneously with chloramphenicol, and addition of trypsin-inactivated CF) also prevent autolysis. This observation emphasizes the indirect or inductive nature of CF on these processes.     

Role of Erythrocytes and Serum in the Nutrition of Rickettsia quintana

Rickettsia quintana grew readily on blood-agar base when the following conditions and supplements were supplied: (i) aerobic conditions; (ii) increased CO(2) tension; (iii) crystalline hemoglobin or hemin, but not protoporphyrin; and (iv) a colloidal "detoxifying agent," such as starch or charcoal. Serum was not required nor did it enhance growth when all of the aforementioned components were supplied.     

MOSQUITO POLLINATION OF HABENARIA OBTUSATA (ORCHIDACEAE)

The floral morphology and pollination of Habenaria obtusata (Orchidaceae) are described. Habenaria obtusata occurs in Alaska, Canada, Norway, Siberia, etc., in great numbers and is pollinated by mosquitoes of the genus Aedes. The pollination process is described as observed in glass cages.     

Electrophoretic characterization of a detergent-treated plasma membrane fraction from corn roots

Experiments were conducted to determine conditions essential for electrophoretic characterization of a detergent-extracted plasma membrane fraction from corn (Zea mays L.) roots. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) initially gave poor resolution of polypeptides in the plasma membrane fraction and, upon detergent treatment for purification of the proton-pumping adenosine triphosphatase (ATPase), showed no enrichment for a 100 kilodalton catalytic subunit characteristic of the ATPase. In contrast to SDS-PAGE, phenol urea acetic acid (PAU)-PAGE clearly resolved two polypeptides in the 100 kilodalton region that were enriched during detergent treatment and indicated at least one polypeptide forms a phosphorylated intermediate characteristic of the ATPase. Problems with SDS-PAGE were found to be caused, in part, by a combination of endogenous proteases and heat-induced aggregation of high molecular weight proteins. The usually standard procedure of boiling the sample prior to SDS-PAGE caused the aggregation of the 100 kilodalton polypeptides. By controlling for proteases using chymostatin and/or phenylmethane sulfonyl floride, and not boiling the sample prior to electrophoresis, two polypeptides were clearly resolved by SDS-PAGE in the 100 kilodalton region of Triton X-114-extracted membranes from corn, oat, barley, and tomato.     

Coordinate initiation of chromosome and minichromosome replication in Escherichia coli.

Escherichia coli minichromosomes harboring as little as 327 base pairs of DNA from the chromosomal origin of replication (oriC) were found to replicate in a discrete burst during the division cycle of cells growing with generation times between 25 and 60 min at 37 degrees C. The mean cell age at minichromosome replication coincided with the mean age at initiation of chromosome replication at all growth rates, and furthermore, the age distributions of the two events were indistinguishable. It is concluded that initiation of replication from oriC is controlled in the same manner on minichromosomes and chromosomes over the entire range of growth rates and that the timing mechanism acts within the minimal oriC nucleotide sequence required for replication.     

Cadmium-Induced Accumulation of Putrescine in Oat and Bean Leaves

The effects of Cd²⁺ on putrescine (Put), spermidine (Spd), and spermine (Spm) titers were studied in oat and bean leaves. Treatment with Cd²⁺ for up to 16 hours in the light or dark resulted in a large increase in Put titer, but had little or no effect on Spd or Spm. The activity of arginine decarboxylase (ADC) followed the pattern of Put accumulation, and experiments with α-difluoromethylarginine established that ADC was the enzyme responsible for Put increase. Concentrations of Cd²⁺ as low as 10 micromolar increased Put titer in oat segments. In bean leaves, there was a Cd²⁺-induced accumulation of Put in the free and soluble conjugated fractions, but not in the insoluble fraction. This suggests a rapid exchange between Put that exists in the free form and Put found in acid soluble conjugated forms. It is concluded that Cd²⁺ can act like certain other stresses (K⁺ and Mg²⁺ deficiency, excess NH₄⁺, low pH, salinity, osmotic stress, wilting) to induce substantial increases in Put in plant cells.     

Discontinuity in DNA replication during expression of accumulated initiation potential in dnaA mutants of Escherichia coli.

Potential for initiation of chromosome replication present in temperature-sensitive, initiation-defective dnaA5 mutants of Escherichia coli B/r incubated at nonpermissive temperature was expressed by shifting to a more permissive temperature (25 degrees C). Upon expression of initiation potential, the rate of [3H]thymidine incorporation varied in a bimodal fashion, i.e., there was an initial burst of incorporation, which lasted 10 to 20 min, then a sudden decrease in incorporation, and finally a second rapid increase in incorporation. Analyses of this incorporation pattern indicated that a round of replication initiated upon expression of initiation potential, but DNA polymerization stopped after replication of 5 to 10% of the chromosome. This round of replication appeared to resume about 30 min later coincident with initiation of a second round of replication. The second initiation was unusually sensitive to low concentrations of novobiocin (ca. 1 microgram/ml) when this inhibitor was added in the presence of chloramphenicol. In the absence of chloramphenicol, novobiocin at this concentration had no detectable effect on DNA replication. It is suggested that cis-acting inhibition, attributable to an attempted second initiation immediately after the first, caused the first round to stall until both it and the second round could resume simultaneously. This DNA replication inhibition, probably caused by overinitiation, could be a consequence of restraints on replication in the vicinity of oriC, possibly topological in nature, which limit the minimum interinitiation interval in E. coli.     

Three-dimensional structure of the T-layer of Bacillus sphaericus P-1.

The three-dimensional structure of the regular surface layer of Bacillus sphaericus P-1 (T-layer) was determined to a resolution of ca. 2.5 nm by electron microscopy and image analysis. The T-layer has P4 symmetry, a lattice constant of 13 +/- 0.2 nm, and a thickness of ca. 8 nm. The reconstruction revealed three distinct domains: a major, a minor, and an arm domain. In the z-direction, the domains are arranged in two planes creating two different surface reliefs.     

Pretreatment with 3-O-methyl-d-glucose or 2-deoxy-d-glucose attenuates the post-mortem rise in rat brain lactate

The present investigation examined the effects of pretreatment with 3-O-methyl-d-glucose (3OMG) or 2-deoxy-d-glucose (2DOG) on post-mortem rise in rat brain lactate to evaluate their potential use for minimizing ischemia-induced rise in brain lactate. The results showed that iv administration of either glucose analogue (2 g/kg) at 2.5 min prior to sacrifice significantly attenuated (to 0.61 of control levels) post-mortem brain lactate rise. Pretreating rats with 2-deoxy-d-glucose (2 g/kg) 15 min prior to sacrifice resulted in a greater inhibition (to 0.52 of control) of the post-mortem lactate rise. The effects of these two analogues (3OMG and 2DOG) can be accounted for by their inhibition of brain glucose transport and inhibition of brain glucose metabolism by 2DOG. The present results suggest that intervention with either of these glucose analogues under the proper experimental procedures may minimize the cytopathological consequences of ischemia related to the rise in brain lactate.