Fine structure of the zoospore ofUlothrix belkae with emphasis on the flagellar apparatus

Summary The anterior end of the zoospore ofUlothrix belkae has been examined in detail and is compared toStigeoclonium and other filamentous green algae. The nature of the symmetry of green algal motile cells is discussed and the term, 180° rotational symmetry, is proposed to describe the type of arrangement of anterior end components seen inU. belkae, including the four basal bodies, rootlets and striated fibers. The four microtubular rootlets are cruciately arranged. A striated microtubule-associated component (SMAC) has a periodicity of 6.4 nm and extends with each 2-membered rootlet posteriorly into the cell. One 5-membered rootlet passes very near the eyespot. Phylogeny in green algal motile cells is discussed.     

Current Productivity and Prehistoric Use of Piñon (Pinus edulis,Pinaceae) in the Dolores Archaeological Project Area,Southwestern Colorado

The possible contribution of pinon (Pinus edulis) seed to the diet of an Anasazi population is investigated using present data on seed productivity and archaeological data on resource use. Annual estimates of total productivity for a 135.7 sq km study area in Montezuma County, Colorado, vary by a factor of 141 in a sample spanning 5 yr. Trees greater than about 25 cm (basal diameter) are usually monoecious and produce significantly more cones per tree but fewer good seeds per cone than smaller, usually dioecious specimens. Archaeological data suggest that piñon seed was a relatively unimportant food item after the initial period of Anasazi colonization of the Dolores River valley about a.D. 600. Use of piñon seed as food was inversely related to degree of agricultural intensification and use of piñon for fuel.     

ULTRASTRUCTURE OF THE FLAGELLAR APPARATUS OF PYROBOTRYS (CHLOROPHYCEAE)1

The flagellar apparatus of Pyrobotrys has a number of features that are typical of the Chlorophyceae, but others that are unusual for this class. The two flagella are inserted at the apex, but they extend to the side of the cell toward the outside of the colony, here designated as the ventral side. Four basal bodies are present, two of which extend into flagella. Four microtubular rootlets alternate between the functional and accessory basal bodies. In each cell, the two ventral rootlets are nearly parallel, but the dorsal rootlets are more widely divergent. The rootlets alternate between two and four microtubules each. A striated distal fiber connects the two functional basal bodies in the plane of the flagella. Two additional, apparently nonstriated, fibers connect the basal bodies proximal to the distal fiber. Another striated fiber is associated with each four-membered rootlet near its insertion into the flagellar apparatus. A fine periodic component is associated with each two-membered rootlet. A rhizoplast-like structure extends into the cell from each of the functional basal bodies. The arrangement of these components does not reflect the 180° rotational symmetry that is usually present in the Chlorophyceae, but appears to be derived from a more symmetrical ancestor. It is suggested that the form of the flagellar apparatus is associated with the unusual colony structure of Pyrobotrys.     

ULTRASTRUCTURE AND TAXONOMIC POSITION OF THE RARE VOLVOCALEAN ALGA,CHLORCORONA BOHEMICA1

Chlorcorona bohemica (Fott) Fott was previously of uncertain taxonomic affinities. The cell to cell connections, which are one of the chief features of the colony, are composed of wall extensions from adjacent cells. The outgrowths are connected by a fine fibrous component extending from wall to wall. The structure of the wall itself and the cell to cell connections, are similar to those of Pyrobotrys, although the connections in the latter are not as elongated. In addition, the flagellar apparatus of Chlorocorona is very similar to the flagellar apparatus of Pyrobotrys, and unlike that in other Chlorophyceae examined. These features suggest that Chlorcorona is closely related to Pyrobotrys and should be referred to the family Spondylomoraceae.     

Viral aggregation: mixed suspensions of poliovirus and reovirus.

The aggregation of mixtures of two dissimilar viruses, poliovirus I (Mahoney) and reovirus III (Dearing), was followed by electron microscopy under conditions known to induce either aggregation or dispersion of each virus separately. Neither virus aggregated at pH 7 in an appropriate buffer, and no mixed aggregates were formed. Under conditions of lowered ionic strength (by dilution into distilled water) poliovirus became aggregated, whereas reovirus did not, and again no mixed aggregates were formed. At pH 6, however, poliovirus again aggregated and, although reovirus did not, it attached to poliovirus aggregates. Thus, some inducement toward aggregation was necessary to cause formation of mixed aggregates. This inducement probably took the form of a reduction of the ionic double layer surrounding the particles, which is known to occur at low pH. At pH 5 and below both viruses aggregated severely, and large mixed aggregates were formed. These mixed aggregates could be broken up by neutralization of the suspension, although small aggregates of poliovirus remained. Reovirus showed a marked tendency to attach to large clumps of poliovirus, but the reverse tendency was not observed. The results indicate that mixed aggregates may be of significance in the isolation of viruses from water or wastewater.     

Spin-trapping of the trichloromethyl radical produced during enzymic NADPH oxidation in the presence of carbon tetrachloride or bromotrichloromethane.

Utilizing the spin-trapping agent phenyl-t-butyl nitrone, a free radical has been detected which is produced from carbon tetrachloride or bromotrichloromethane during the enzymic oxidation of NADPH by rat liver microsomes. The presence of NADPH is obligatory for generation of the radical. The formation of the trichloromethyl radical-phenyl-t-butyl nitrone adduct is an enzymic process, as evidenced by the inhibition of its formation in systems containing heated microsomes and in systems containing p-hydroxymercuribenzoate. A computer-simulated ESR spectrum for the trichloromethyl adduct of phenyl-t-butyl nitrone can reproduce the essential features of the spectrum of the spin-trapped radical produced enzymically from CCl4. A mechanism is proposed for the formation of the trichloromethyl radical from CCl4 or BrCCl3.     

Evidence for vitamin K semiquinone as the functional form of vitamin K in the liver vitamin K-dependent protein carboxylation reaction.

The protein carboxylating system derived from vitamin K-deficient rat liver microsomes functions in detergent solution if vitamin K₁, NADH, dithiothreitol, CO₂ and O₂ are added. The requirements for added NADH, dithiothreitol and O₂ are all eliminated by the use of vitamin K₁ hydroquinone in place of quinone. The use of the hydroquinone gives a more rapid reaction and a higher yield than does the quinone plus reducing system. The reaction proceeding from either the vitamin K₁ quinone or hydroquinone is blocked by the spin-trapping agent, 5,5-dimethyl-l-pyrroline-N-oxide, suggesting that the active form of vitamin K is the semiquinone.     

Mixed-mode hydrophobic ion exchange for the separation of oligonucleotides and DNA fragments using HPLC

Hydrophobic anion exchangers were formed by cobonding both ionic and hydrophobic ligands to silica gel. These phases were used to separate single-stranded oligonucleotides and double-stranded DNA restriction fragments. By varying the ratio of n-octyldimethylsilane and either 3-chloropropyldimethylsilane or 4-chlorobutyldimethylsilane added during silanization a series of mixed-ligand or mixed-mode stationary phases was created. Concentration and ratio of bonded ligands were determined using a new gas chromatography fluorination method. Total ligand coverage was found to approach 2.1 ligands nm-2 for n-octyldimethylsilane. Bonding reproducibility for mixed-mode phases was good. Nucleic acid separations were achieved under gentle mobile phase conditions by using the stationary phase as an easily modifiable variable.     

Inhibition of mutation and combating the evolution of antibiotic resistance

The emergence of drug-resistant bacteria poses a serious threat to human health. In the case of several antibiotics, including those of the quinolone and rifamycin classes, bacteria rapidly acquire resistance through mutation of chromosomal genes during therapy. In this work, we show that preventing induction of the SOS response by interfering with the activity of the protease LexA renders pathogenic Escherichia coli unable to evolve resistance in vivo to ciprofloxacin or rifampicin, important quinolone and rifamycin antibiotics. We show in vitro that LexA cleavage is induced during RecBC-mediated repair of ciprofloxacin-mediated DNA damage and that this results in the derepression of the SOS-regulated polymerases Pol II, Pol IV and Pol V, which collaborate to induce resistance-conferring mutations. Our findings indicate that the inhibition of mutation could serve as a novel therapeutic strategy to combat the evolution of antibiotic resistance.     

Differential single-stranded DNA binding properties of the paralogous SsbA and SsbB proteins from Streptococcus pneumoniae

The naturally transformable Gram-positive bacterium Streptococcus pneumoniae has two single-stranded DNA-binding (SSB) proteins, designated SsbA and SsbB. The SsbA protein is similar in size to the well characterized SSB protein from Escherichia coli (SsbEc). The SsbB protein, in contrast, is a smaller protein that is specifically induced during natural transformation and has no counterpart in E. coli. In this report, the single-stranded DNA (ssDNA) binding properties of the SsbA and SsbB proteins were examined and compared with those of the SsbEc protein. The ssDNA binding characteristics of the SsbA protein were similar to those of the SsbEc protein in every ssDNA binding assay used in this study. The SsbB protein differed from the SsbA and SsbEc proteins, however, both in its binding to short homopolymeric dT(n) oligomers (as judged by polyacrylamide gel-shift assays) and in its binding to the longer naturally occurring X and M13 ssDNAs (as judged by agarose gel-shift assays and electron microscopic analysis). The results indicate that an individual SsbB protein binds to ssDNA with an affinity that is similar or higher than that of the SsbA and SsbEc proteins. However, the manner in which multiple SsbB proteins assemble onto a ssDNA molecule differs from that observed with the SsbA and SsbEc proteins. These results represent the first analysis of paralogous SSB proteins from any bacterial species and provide a foundation for further investigations into the biological roles of these proteins.