Search PubMed⌕ Search

Biomedical subjects

L D Witter

Publications and source records attributed to L D Witter.

26 records · Page 2Linked to original sources
PubMed1969

Influence of temperature on glucose utilization by Pseudomonas fluorescens.

The influence of temperature on the conversion of glucose into cell material and into energy for maintenance was determined for Pseudomonas fluorescens by a steady-state turbidity method and by a substrate utilization method. Conversion of glucose into cell material was measured as yield; conversion of glucose into energy for maintenance was measured as specific maintenance, the minimum dilution rate in continuous culture below which a steady state is not possible. The values obtained by the two methods were nearly identical; with both, the yield and specific maintenance decreased with decreasing temperature. The specific maintenance consumption rate (milligrams of glucose taken up per milligram of cell dry weight per hour at zero growth) was also calculated by the substrate utilization method and found to decrease with decreasing temperature. However, the amount of glucose consumed per generation for maintenance increased with decreasing temperature. This increased glucose consumption for maintenance may provide a partial explanation for the decrease in yield at low temperatures. Small amounts of glucose were also converted into pigment at all temperatures tested, with the greatest amount formed at 20 C.

Bacteriological Techniques↗
PubMed1968

Thermal injury and recovery of Streptococcus faecalis.

Exposure of Streptococcus faecalis R57 to sublethal heating produced a temporary change in the salt tolerance and growth of the organism. After sublethal heat treatment at 60 C for 15 min, greater than 99.0% of the viable population was unable to reproduce on media containing 6% NaCl. In addition, the heated cells displayed a sensitivity to incubation temperature, pH, and 0.01% methylene blue. When the injured cells were placed in a synthetic medium, recovery occurred at a much slower rate than in a complex medium. However, both media supported comparable growth of the uninjured organism. Various media used for the enrichment of streptococci also provided a suitable environment for the recovery of the injured cells. Generally, as more selective agents were present in the medium, the rates of recovery decreased. Metabolic inhibitor studies with chloramphenicol, penicillin, and actinomycin D substantiated the fact that the process involved was recovery and not growth, and that this recovery was linked to ribonucleic acid synthesis.

Acid-Base Equilibrium↗
PubMed1968

Glycerol ester hydrolase activity of lactic acid bacteria.

Seventeen strains of lactic acid bacteria were assayed for their glycerol ester hydrolase activity by using an improved agar-well technique, and eight strains by determining the activity in cell-free extracts using a pH-stat procedure. All cultures tested showed activity and hydrolyzed tributyrin more actively than they did tricaproin. The cell extract studies demonstrated that the cells contained intracellular esterases and lipases. The culture supernatant fluid was without activity. The lipase and the esterase differed in their relative activity to each other in the different extracts and in the ease by which they could be freed from the cellular debris. It is suggested that the lipase of these organisms is an endoenzyme and the esterase an ectoenzyme.

Cell-Free System↗
PubMed1967

Culture aeration in a polythermostat.

A system for the aeration of cultures growing in a polythermostat temperature-gradient block was developed. This system provided both aeration and agitation of the cultures, while allowing the growth to be followed spectrophotometrically. The necessity for aeration of cultures growing in a polythermostat was experimentally shown.

Bacteriological Techniques↗
PubMed1967

Continuous Propagation of Trichosporon cutaneum in Cheese Whey.

Trichosporon cutaneum, a nonfermenting yeast, was used to convert cheese whey lactose into microbial cell material. The doubling time for this organism in a laboratory-scale continuous propagator was 2 hr in a whey medium fortified with ammonium sulfate and corn steep liquor. Cellular growth and efficiency of conversion of lactose to cell material was higher than with Saccharomyces fragilis. When grown in whey, the nitrogen content of T. cutaneum was 3.5% and the distribution of amino acids per gram of cell protein was similar to that of commercial food yeasts.

Journal Article↗