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P S Dawson

Publications and source records attributed to P S Dawson.

At least 19 recordsLinked to original sources
PubMed1988

An experimental analysis of the relationships between fitness components and malic enzyme genotypes in Tribolium confusum.

The hypothesis that natural selection is capable of maintaining allozyme variation in natural populations was tested using a species of flour beetles, Tribolium confusum. We selected a polymorphic locus (a locus encoding variation for malic enzyme) in an experimental population of T. confusum and scored the genotypes at this locus for a series of fitness components on different flour types. Measurements included survival rate, development time, fecundity, and rate of egg cannibalism. Flour type had significant effects on most traits. Significant differences among genotypes for fecundity and rates of egg cannibalism and the presence of genotype x flour type interactions for development time were demonstrated. Thus, changes in allele frequencies at the malic enzyme locus could in part be under the influence of natural selection. The existence of genotype x flour type interactions suggests that environmental heterogeneity could maintain allozyme variation at the malic enzyme locus.

Animals↗
PubMed1983

X-linked and autosomal inheritance patterns of homologous genes in two species of Tribolium.

The tenebrionid beetles Tribolium castaneum and T. confusum are representative of two distinct species groups within their genus. It has been suggested [Smith, S.G. (1952). J. Morphol. 91:325] that the 8AA + neo-XY karyotype of T. confusum was derived from the ancestral 9AA + XY formula, still present in T. castaneum, via the fusion of one pair of autosomes with the X and Y chromosomes during the early divergence of the confusum and castaneum species groups. In the present paper, electrophoretic variation in malic enzyme and hexokinase-1, detected in laboratory strains in Tribolium, is described. Evidence is presented that the genes encoding variation in both enzymes are autosomal in T. castaneum but are X linked in T. confusum. These species-specific patterns of inheritance of homologous gene loci are consistent with the hypothesized karyotypic history of the genus.

Animals↗
PubMed1980

VIDA II: a computerised diagnostic recording system for veterinary investigation centres in Great Britain.

"Veterinary Investigation Diagnosis Analysis" II is a computerised recording system for all the diagnoses made at 33 Government diagnostic laboratories in Great Britain. It was created in 1975 and the records of 150,000 specimens are stored on it each year. The system depends on an agreed list of 393 possible diagnoses (101 cattle, 96 sheep, 72 pigs, 71 birds and 53 for other species). Diagnostic records are sent each month to a computer centre which produces an annual record of all diagnoses made and a monthly record of the number of submissions and financial charges. The computer file can be interrogated from a terminal at the epidemiology unit Weybridge and the diagnostic records are available to research workers.

Animal Diseases↗
PubMed1980

Differential growth rates of Candida utilis mother and daughter cells under phased cultivation.

The yeast Candida utilis was continuously synchronized by the phased method of cultivation with the nitrogen source as the growth-limiting nutrient. The doubling time (phasing period) of cells was 6 h. Both cell number and deoxyribonucleic acid synthesis showed a characteristic stepwise increase during the phased growth. The time of bud emergence coincided with the time of initiation of deoxyribonucleic acid synthesis. Size distribution studies combined with microscopic analysis showed that the cells expanded only during the unbudded phase of growth. Usually the cells stopped increasing in size about 30 min before bud emergence, and the arrest of the increase in cell volume coincided with the exhaustion of nitron from the medium. There was no net change in the volume of cells during the bud expansion phase of growth, suggesting that as the bud expanded, the volume of the mother portion of the cell decreased. After division the cells expanded slightly. The postdivision expansion of cells, unlike the growth before bud initiation, occurred in the absence of the growth-limiting nutrient. The newly formed daughter cells were smaller than the mother cells and expanded at a faster rate, so that both types of cells reached maximum size at the same time. Possible reasons for the different rates of expansion of mother and daughter cells are discussed.

Ammonia↗
PubMed1980

Relationship between cell size and efficiency of synchronization during nitrogen-limited phased cultivation of Candida utilis.

Under the phased method of cultivation the yeast Candida utilis grew and divided synchronously. The newly formed cells were relatively small, and a new cell cycle was not initiated until the cells could attain a certain minimum size (critical size). Although the cells expanded to some extent after division, the critical size was not reached until a fresh supply of medium was provided. With the arrival of the fresh supply of growth medium at the beginning of the phasing period, the cells expanded rapidly, and new cell cycles were initiated. The cells continued to expand until the growth-limiting nutrient (nitrogen source) was exhausted or until 90 min, which ever occurred first. Usually, buds emerged at a constant time after the start of the phasing period. The time of bud emergence was independent of the size attained by the cells during the expansion phase of growth. The results indicated that it was initiation of the cell cycle that was under size control, and not bud emergence. Bud emergence seemed to be under the control of a timer. The start of this timer seemed to be at or immediately after the beginning of the phasing period. Protein synthesis was essential for the initiation and expansion of buds. However, inhibition of protein synthesis by cycloheximide did not prevent unbudded cells or the parent portion of budded cells from expanding. Cycloheximide seemed to abolish the control mechanism(s) which prevented the cells from expanding after they had reached the maximum size.

Ammonium Sulfate↗
PubMed1978

Relationship between iron-limited growth and energy limitation during phased cultivation of Candida utilis.

The yeast Candida utilis was continuously synchronized by the phasing technique (6 h doubling time) with either iron or nitrogen as the limiting nutrient. Iron limitations resulted in decreased molar growth yields with respect to the carbon substrates and ammonia and in increased specific rates of oxygen uptake. Relatively low energy-charge values were maintained by the iron-limited culture. All these taken together seemed to indicate that the growth of the yeast under iron limitation was also limited by metabolically available energy. Consideralbe amounts of ethyl acetate were produced by the yeast under phased cultivation when the growth was limited by iron but not by nitrogen. In vitro studies using cell-free extracts showed that the substrates for ethyl acetate synthesis were acetyl coenzyme A (acetyl CoA) and ethanol. Under iron-limited growth acetyl CoA seemed to be diverted to ethyl acetate formation rather than being oxidized through the tricarboxylic acid (TCA) cycle. The possibility of energy limitation under iron-limited growth being brought about by the reduced capacity of the yeast to oxidize acetyl CoA through the TCA cycle is considered.

Acetates↗
PubMed1977

Variations in the adenylate energy charge during phased growth (cell cycle) of Candida utilis under energy excess and energy-limiting growth conditions.

The variations in the levels of adenine nucleotides during the phased growth (cell cycle) of the yeast Candida utilis growing under nitrogen, sulfate, or iron limitation with glycerol as carbon source have been determined. Synchronous cultures were obtained by the continuous phasing technique, and the results were compared with those of chemostat cultures growing at similar growth rates and under the same types of nutrient limitation. Whereas the chemostat experiments indicated only the average energy status of cultures growing at random, results from phased cultures showed that the adenylate energy charge, defined as (ATP + (1/2)ADP)/(ATP + ADP + AMP) (where ATP, ADP, and AMP signify adenosine 5'-triphosphate, -diphosphate, and -monophosphate, respectively), varied during the phased growth of the yeast. These variations were related to the stage of development of the cells and to the type of nutrient limitation. In every case the energy charge dropped to a low value during the first half of the phasing cycle (cell cycle). Whereas the energy charge was maintained at relatively high levels (ranging from 0.78 to 0.94), for sulfate- or nitrogen-limited cultures, it was very low when iron was the growth-limiting nutrient (0.44 to 0.78). In spite of the low energy charge, the yeast continued to grow under iron limitation. The main component of the adenylate pool of the iron-limited culture was ADP and not ATP as observed with other types of nutrient limitation. It is concluded that under iron limitation the growth of the organism is limited by energy and that under energy-limited growth the energy charge of a growing organism is maintained at low levels. The reason for maintaining a low energy charge in an energy-limited culture is discussed.

Adenine Nucleotides↗
PubMed1977

Radiorespirometry of Candida utilis in phased culture under nitrogen-, carbon-, and phosphorus-limited growth.

The release of 14CO2 from specifically labelled glucose ([G-1-14C],[G-2-14C],[G-3,4-14C], and [G-6-14C]) by phased cells of C. utilis was examined at intervals during 6-h cycles under conditions of N-,P-, and C-limited growth. On the basis that the release of 14CO2 from [G-1-C14] could serve as a measure of hexose monophosphate pathway (HMP) activity, of 14CO2 from [G-3,4-14C] as a measure of Embden-Meyerhof-Parnas (EMP) activity, and 14CO2 from [G-6-14C] as indicative of tricarboxylic acid (TCA) cycle activity, it was concluded that a relatively uniform operation of EMP occurred throughout the cycle in N-, P-, and C-limited cells, and of HMP and TCA in C-limited cells, but considerable variations took place in HMP and TCA cycle activities in N- and P-limited cells. The patterns of 14CO2 released from [G-2-14C] were more closely related to those observed from [G-1-14C] and [G-3,4-14C] than from [G-6-14C]. Changes in the rate of 14CO2 evolution during the cycle were sometimes abrupt and likely coincided with 'critical points' of metabolic activity in the cycle.

Candida↗
PubMed1976

Some comparative observations on the relative contributions of alternate pathways in the metabolism of glucose by Candida utilis.

Candida utilis was grown in batch, chemostat, and continuously synchronised (phased) culture on a nitrogen-limited glucose mineral salts medium: phosphorus- and carbon-limited phased cultures were also used. The 14CO2 evolved from [G-1-14c]and [G-6-14c] was used, as a simple C1/C6 ratio, to observe the relative changes in EMP and HMP contributions during growth of the cultures. The ratio varied during the cell cycle, and changed with growth rate, and with nutrient limitation. The changes generally indicated that the HMP predominated, most notably in the early part of the batch-growth sequence and early in the cell cycle. The overall results reflected the relative merits of the different cultivation techniques for examining microbial metabolism: the advantage of a greater resolution by the synchronised method, based upon the unit performance rather than the randomised mean performance of the cell population...

Candida↗
PubMed1975

Changes in pattern of respiration and glucose utilisation in Candida utilis during the cell cycle: some variations with growth rate.

The release of 14CO2 from 14C-labelled glucose(G-1(-14)C, G-3,4(-14)C, G-6(-14)C) was followed in phased cultures of Candida utilis grown in a glucose- mineral salts medium under altered conditions of carbon:nitrogen limitation at doubling times of 2,4 and 6, h. Changes in oxygen uptake and CO2 evolution were observed and respirometric studies showed that the relative contributions of the Embden-Meyerhof-Parnas and hexose monophosphate pathways varied over the cell cycle and changed with growth rate. The results are discussed in relation to the growth metabolism of the cells.

Candida↗