Chemical flocculability of sludge organisms in response to growth conditions

The effect of waste characteristics on the removal of suspended solids and soluble phosphorus by alum, Al₂(SO₄)₃·18H₂O, was investigated in an activated sludge system with no cellular recycle. Under the conditions presently studied, it was found that sludge organisms grown in nitrogen- and phosphorus-restricted media possess exceptionally large capsules and produce a higher surface electric charge per unit of fry weight. Chemical demand for separation of these capsulated cells is obviously higher than those solids cultivated under a well-balanced nutrient condition. For phosphorus removal, the molar ratio of Al⁺³:P is a function of the initial concentrations of soluble phosphorus and suspended solids in solution. The relationship between percent phosphorus removal and the quantity of chemical coagulent used shows nonstoichiometric relationship; that is, the required molar ratio of Al⁺³:P is always greater than one and directly depends upon the content of suspended solids in the flocculated media. Moreover, the present study indicated that chemical separation of dispersed microorganisms occurred following phosphorus removal.     

Population biology of avena. VI. The role of genetic polymorphisms in the outcome of interspecific competition

Three different series of population samples of two Avena species cooccurring in California were grown for an analysis of the role of genetic variation in interspecies competition: I, samples from mixed fatua-barbata sites in nature, grown in mixed stands; II, samples from pure sites and grown in pure stands, and III, the same sites as in II but grown in mixed stands. Four macroenvironments and four densities were used giving a total of sixteen entries for each genetic/competitive unit in order to measure both mean and variance of survival and reproductive rates as fitness characters. Sites used in each series included low versus high levels of genetic polymorphism within each species. In general, high polymorphism favored A. fatua in competition with monomorphic A. barbata, and high polymorphism in A. barbata allowed it to compete better with monomorphic A. fatua observation fits well into the pattern of reduced polymorphism in natural mixed stands. Mean performance of polymorphic mixed stands was not consistently higher than the monomorphic combinations or pure stands but the greater relative stability over environments seemed to favor polymorphisms in one or both of the competitors. A relatively less regular pattern of density or competitive response in series III was interpreted as evidence for the lack of coadaptedness between samples drawn from pure sites. Several limitations characteristic of such controlled studies were briefly discussed; however, the tentative conclusions from laboratory studies provided several promising clues for more critical field studies.This work was supported in part by a grant from the National Science Foundation (GB 8627).     

Metabolism of polyadenylic acid sequences during germination of blastocladiella emersoni: Zoospores.

The metabolism of the poly(A) sequences isolated from Blastocladiella emersonii was followed during the first hour of germination. Poly (A) sequences synthesized during the first 30 min of germination do not undergo detectable changes in size. During the first 45 min of germination, poly(A) sequences synthesized during zoosporogenesis decrease in size to the extent that there is essentially no size overlap between poly(A) fragments which were present in the zoospore and newly synthesized poly(A) sequences. The results presented indicate that during germination, polyadenylation occurs in RNA molecules which were present in the zoospore but lacked poly(A) sequences. No detectable size differences were observed between poly(A) sequences added to newly synthesized RNA compared to those added to the nonpolyadenylated RNA present in the zoospore during germination. Cycloheximide did not prevent the observed decrease in size of the poly(A) sequences during germination.     

Nucleotide recognition seouence at the cleavage site of Haemophilus aegyptius II (Hae II) restriction endonuclease

We have determined the nucleotide sequence recognized by the restriction endonuclease Hae II from Haemophilus aegyptius which cleaves the simian virus 40 (SV40) DNA at a single specific site. By using terminal radioactive labeling of the cleavage site at both the 5′ and 3′-ends we have deduced the recognition sequence,

with elements of a two-fold rotational symmetry. The endonuclease produces staggered ends with protruding 3′-terminated single-strands, four nucleotides in length. In plasmid RSF 2124 DNA, which contains multiple Hae II cleavage sites, it was observed that the 5th nucleotide from the 3′ terminus is either a pdA or a pdG, indicating alternating recognition sequences.     

Measurement of the translational mobility of concanavalin A in glycerol-saline solutions and on the cell surface by fluorescence recovery after photobleaching.

The fluorescence recovery kinetics of succinyl-fluorescein Concanavalin A (S-F-ConA) in glycerol-physiological saline solutions of high viscosity and when bound to the surface of mouse fibroblasts were measured following brief photobleaching using a laser excited fluorescence microscope. In the high viscosity solutions, the recovery kinetics, interpreted on the basis of a simple diffusion model, yielded a diffusion coefficient in close agreement with the values predicted by the Stokes-Einstein equation. Recovery kinetics for S-F-ConA bound to the surface of mouse 3T3 and SV3T3 cells cultured in vitro yielded diffusion coefficients in the range of 5-10-10(-11) cm2/s, values considerably lower than those reported previously for membrane proteins. These measurements indicated that a considerable fraction of the S-F-ConA molecules bound to the cell surface are immobilized. These results are discussed in relation to current concepts of lateral motion of protein components within natural membranes.     

Interactions of aminopyridines with potassium channels of squid axon membranes.

The effects of aminopyridines on ionic conductances of the squid giant axon membrane were examined using voltage clamp and internal perfusion techniques. 4-Aminopyridine (4-AP) reduced potassium currents, but had no effect upon transient sodium currents. The block of potassium channels by 4-AP was substantially less with (a) strong depolarization to positive membrane potentials, (b) increasing the duration of a given depolarizing step, and (c) increasing the frequency of step depolarizations. Experiments with high external potassium concentrations revealed that the effect of 4-AP was independent of the direction of potassium ion movement. Both 3- and 2-aminopyridine were indistinguishable from 4-AP except in potency. It is concluded that aminopyrimidines may be used as tools to block the potassium conductance in excitable membranes, but only within certain specific voltage and frequency limits.