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T D BROCK

Publications and source records attributed to T D BROCK.

At least 19 recordsLinked to original sources
PubMed1965

ELECTRON MICROSCOPY OF CELL FUSION IN CONJUGATING HANSENULA WINGEI.

Conti, S. F. (Dartmouth Medical School, Hanover, N.H.), and T. D. Brock. Electron microscopy of cell fusion in conjugating Hansenula wingei. J. Bacteriol. 90:524-533. 1965.-The heterothallic yeast Hansenula wingei is a favorable organism for the study of the process of cell fusion, since strong agglutination of cells of the two mating types ensures a high percentage of cell fusions. The initial agglutination reaction results in cell-wall deformation, so that the walls in the region of contact are tightly appressed over an extensive area. The fusion process is initiated when the walls of two cells elongate, and this elongation seems to be restricted to the region where the cells touch. Occasionally, one cell is seen to push in the wall of the other, but in many cases both cells elongate equally, as would be expected in an isogamous organism. The precise disposition of the elongating wall probably reflects the manner in which the cells initially become associated in the agglutinated cell clump. Soon after wall elongation begins, cell-wall fusion occurs along the margin of contact. Only after fusion is complete is the wall separating the two cells dissolved away. If wall dissolution begins at one edge of the conjugation tube, a flap is formed in which can be seen the remnants of the fused walls. Alternatively, dissolution can begin at the center of the conjugation tube, proceeding towards the outside. Conjugating cells are uninucleate, and the nuclei are large and frequently lobed or elongated. After the conjugation tube is formed, the nuclei migrate towards the center, and fusion occurs only over a small region where the nuclear membranes come in contact. After nuclear fusion, the first diploid bud forms from the conjugation tube and at right angles to the tube axis. The diploid nucleus then migrates into this bud. Frequently, in the later stages of conjugation, a large vacuole develops in each of the original cells. All of the above events will occur in a medium devoid of a nitrogen source and in which vegetative budding will not occur.

Cell Biology↗
PubMed1964

KNOTS IN LEUCOTHRIX MUCOR.

The filaments of Leucothrix mucor are able to form true knots under certain cultural conditions. Such structures have apparently not been previously seen in filamentous organisms. As the culture ages, the knots become tighter and eventually the cells in the knot region fuse and form a large bulb. The filament breaks on each side of the bulb, and two shorter filaments anda free bulb are produced. The free bulbs have not been observed to grow into new filaments.

Bacteria↗
PubMed1964

HOST RANGE OF CERTAIN VIRULENT AND TEMPERATE BACTERIOPHAGES ATTACKING GROUP D STREPTOCOCCI.

Brock, Thomas D. (Indiana University, Bloomington). Host range of certain virulent and temperate bacteriophages attacking group D streptococci. J. Bacteriol. 88:165-171. 1964.-Host range studies with five bacteriophages isolated from sewage showed that a high degree of strain specificity occurred among the species Streptococcus faecalis, S. faecalis var. zymogenes, and S. faecalis var. liquefaciens. Certain phages were able to attack various members of these subgroups but not other members. A high degree of strain specificity was also found with respect to eight phages attacking strains of S. faecium. Many strains of this latter group were resistant to all the phages available. The only firm conclusion was that no phage attacked both S. faecium and S. faecalis strains. In several selected strains of the S. faecalis-liquefaciens-zymogenes group, resistance to several virulent phages seemed to be related to the presence of certain prophages in these strains. A search for transduction with the temperate phages was unsuccessful. Mutants of S. faecium 8043 resistant to certain growth-factor analogues showed unpredictable changes in resistance and sensitivity to two virulent phages.

Bacteriophage Typing↗
PubMed1963

STREPTOMYCIN AS AN ANTIVIRAL AGENT: MODE OF ACTION.

In host bacteria resistant to the antibiotic, streptomycin inhibits phage replication by inhibiting the process of injection. This effect is competitively reversed by certain divalent cations, polyamines, and streptidine. It is proposed that streptomycin inhibits injection by attaching to the phage DNA while it is still folded within the phage head, and in this way it prevents the unfolding which is essential for the injection process. The reversal agents probably function by displacing the antibiotic from the phage, but they also promote injection themselves.

Agar↗
PubMed1963

EFFECT OF ANTIBIOTICS AND INHIBITORS ON M PROTEIN SYNTHESIS.

Brock, Thomas D. (Western Reserve University, Cleveland, Ohio). Effect of antibiotics and inhibitors on M protein synthesis. J. Bacteriol. 85:527-531. 1963.-This work extends the observations of Fox and Krampitz on M protein synthesis in nongrowing cells of streptococci. A survey of a large number of antibiotics and other potential inhibitors was made. Some substances bring about inhibition of fermentation and inhibit M protein synthesis because they deprive the cell of the energy needed for this process. A second group of substances inhibit growth at concentrations tenfold or more lower than they inhibit M protein synthesis. These are the antibiotics which inhibit synthesis of cell wall or other structures in growing cells, but do not affect protein synthesis. A third group of substances inhibit growth and M protein synthesis at the same concentration. These substances probably inhibit growth because they inhibit general protein synthesis, and are therefore specific inhibitors of protein synthesis. In this class are chloramphenicol, erythromycin, and the tetracyclines. Several other antibiotics of previously unknown mode of action are in this class. A fourth group of substances had no effect on M protein synthesis. No substances were found which inhibited M protein synthesis at a lower concentration than that which inhibited growth. M protein synthesis in nongrowing cells may be a useful model system for obtaining a detailed understanding of protein synthesis.

Anti-Bacterial Agents↗
PubMed1963

SURVEY OF THE BACTERIOCINES OF ENTEROCOCCI.

Brock, Thomas D. (Indiana University, Bloomington), Barbara Peacher, and Deborah Pierson. A survey of the bacteriocines of enterococci. J. Bacteriol. 86:702-707. 1963.-A survey has been made of bacteriocine production by a wide variety of well-characterized strains of group D streptococci. On the basis of spectrums and sensitivity to chloroform, heat, and proteolytic enzymes, five distinct bacteriocines can be defined. Type 1 is produced by all Streptococcus zymogenes (S. faecalis var. zymogenes) strains, is active against a wide variety of gram-positive bacteria, and is also a hemolysin. Type 2 is produced by some S. liquefaciens (S. faecalis var. liquefaciens) strains, and acts on many enterococci as well as on certain other lactic acid bacteria. Type 3 is produced by certain strains of both S. faecalis and S. faecium, and inhibits a wide variety of group D streptococci, but is inactive against all other lactic acid bacteria tested except Leuconostoc citrovorum. Type 4 is produced by certain S. faecium strains and resembles in certain ways the type 3 activity, but differs from it in other ways. Type 5 has been found to be produced by only one proteolytic strain of S. zymogenes, and this bacteriocine has a very narrow spectrum. The strain that produces this bacteriocine also produces type 1 activity. No strain is sensitive to a bacteriocine of the type it produces.

Bacillus cereus↗
PubMed1963

PROBABLE IDENTITY OF A GROUP D HEMOLYSIN WITH A BACTERIOCINE.

Brock, Thomas D. (Indiana University, Bloomington) and Joseph M. Davie. Probable identity of a group D hemolysin with a bacteriocine. J. Bacteriol. 86:708-712. 1963.-All strains of Streptococcus zymogenes (S. faecalis var. zymogenes) produce a bacteriocine which is active against lactic acid bacteria and most other grampositive bacteria. Mutants which have lost the hemolytic characteristic lose at the same time their bacteriocine-producing ability. A strain which was resistant to the bacteriocine but which was nonhemolytic and nonbacteriocinogenic was irradiated, and two hemolytic mutants were isolated from it. These mutants were also bacteriocinogenic. Thus, the two activities are gained or lost together by mutation. Both activities are destroyed by chloroform vapors and are antagonized by lecithin. Both activities are destroyed at the same rate by treatment at 45 C under mildly acid conditions, and both activities are stable when heated in agar. The two activities are produced in parallel during the growth cycle, and disappear in parallel. The possible ecological role of a substance which is both a hemolysin and a bacteriocine is discussed.

Bacteriolysis↗
PubMed1962

Magnesium binding as an explanation of the mode of action of novobiocin.

Novobiocin affects a wide variety of biochemical and biological processes in bacteria, whereas most other antibiotics seem to affect one specific process. All of the processes known to be affected by novobiocin require magnesium ions, and in a number of cases magnesium deficiency mimics the action of the antibiotic. Evidence is presented that novobiocin complexes with magnesium ions.

Anti-Bacterial Agents↗
PubMed1962

Effects of magnesium ion deficiency on Escherichia coli and possible relation to the mode of action of novobiocin.

Brock, Thomas D. (Indiana University, Bloomington). Effects of magnesium ion deficiency on Escherichia coli and possible relation to the mode of action of novobiocin. J. Bacteriol. 84:679-682. 1962.-Cells of Escherichia coli ML35 grew in magnesium-deficient medium at an arithmetic rate for 4 to 5 hr. In the later stages of this period, the viability of the cells decreased, ribonucleic acid was lost, and the cells became able to hydrolyze o-nitro-phenyl-beta-d-galactoside at a much increased rate. Further, the cells became filamentous and stained less intensely with methylene blue. Since magnesium ions are known to stabilize cell membranes, the changes are interpreted as due to alterations in membrane integrity. Novobiocin induced the same changes as magnesium ion deficiency, providing further support for the hypothesis that novobiocin acts by inducing a magnesium ion deficiency.

Cell Membrane↗