Slow Feeding Research Articles

An estimate of the size of the metacyclic variable antigen repertoire of Trypanosoma brucei rhodesiense.

A group of 27 variable antigen type (VAT)-specific monoclonal antibodies (McAbs) have been made against metacyclic forms of a cloned stock of Trypanosoma brucei rhodesiense. In combination, these labelled in immunofluorescence 99.3% of trypanosomes in salivary probes from tsetse flies. The 0.7% of unlabelled trypanosomes were believed to be uncoated forms. The ability of a mixture of antibodies to kill metacyclics in vitro by complement-mediated lysis, thus neutralizing their infectivity for mice, was tested. The antibody mixture consisted of 24 McAbs plus 3 VAT-specific rabbit antisera. In 12 replicate experiments this mixture of antibodies prevented infection of mice. Parallel controls showed that neutralization was probably antibody-mediated and VAT specific. However, we have not been able to repeat these results on a long-term basis; this may be due to a loss of neutralizing activity by one of the McAbs. The successful neutralization experiments indicate that the number of VATs in the metacyclic repertoire of one stock of T. b. rhodesiense is limited to at most 27.

Biogenic amines in Drosophila melanogaster selected for differences in larval feeding behavior

Levels of biogenic amines were assayed in lines of Drosophila melanogaster selected for differences in their rate of larval feeding activity. Noradrenaline levels were low in one of the fast feeding lines (FA), but not in a second fast feeding line (FB). Dopamine levels were high in one of the slow feeding lines (SA) and low in the fast feeding line (FB). There were no significant differences in serotonin levels between the selected lines. The biochemical findings differ from those reported in previous studies on locomotor activity in adult flies. The results are consistent with the view that similar behavioral phenotypes may arise from different genetic and biochemical bases.

Genetic analysis of larval feeding behaviour in Drosophila melanogaster.

SUMMARYThe larvae ofDrosophila melanogasterfeed continuously during their period of development. The rate of feeding activity, measured as the number of cephalopharyngeal retractions per minute, varies with the physiological age of the larva. Feeding rate responded readily to directional selection to give rise to non-overlapping populations with fast and slow feeding larvae, respectively. Realized heritabilities for the character from different selected lines varied between 11 and 21%. Crosses between the selected populations show significant dominance for fast feeding rate and appreciable non-allelic gene interaction. Larvae of the slow feeding populations showed a correlated reduction in locomotor activity but fast feeding larvae do not move about significantly faster than the unselected controls. Asymmetry of the correlated response to selection, it is argued, is due to selection in the slow feeding populations of alleles with a secondary effect in both behaviours.

Regulation of pectate lyase synthesis in Pseudomonas fluorescens and Erwinia carotovora.

Inducible synthesis of extracellular pectate lyase occurs in Erwinia carotovora, a bacterial soft-rot pathogen of plants, and, to a lesser extent, in a nonpathogenic isolate of Pseudomonas fluorescens. A combination of pectin and a heat-labile factor in fresh potato tissue or acetone powders of the tissue provided the best carbon source for induction. Yields of inducible pectate lyase were much greater than those usually reported. The pathogen, but not the saprophyte, produced a small amount of constitutive enzyme when grown on glucose. The relatively low level or absence of constitutive synthesis in these bacteria did not result from catabolite repression. Attempts were made to relieve any existing catabolite repression by restricting growth through slow feeding of glucose or by growing the organisms on glycerol. These conditions did not significantly alter the differential rate of lyase synthesis compared with changes observed in the presence of inducers. Previous growth history did not affect induction in the pathogen. However, P. fluorescens previously cultured on glucose required 10 to 20 generations of growth on inducing medium before appreciable lyase synthesis occurred. Differences between the pathogen and nonpathogen suggest that regulation of pectate lyase synthesis is related to pathogenicity of soft-rot bacteria.

Comparative metabolism of vegetative and sporulating cultures of Clostridium thermosaccharolyticum.

Cultures of Clostridium thermosaccharolyticum, under conditions of restricted growth achieved by slow feeding of glucose, showed a high degree of sporulation. Analysis of the end products showed an accumulation of ethyl alcohol in addition to butyrate and acetate, whereas, in the nonsporulating cultures, acetate and butyrate were the principal products. Incorporation of uniformly labeled (14)C-glucose by sporulating cells was three to four times higher than by nonsporulating cells. The efficiency of acetate assimilation into the lipid fraction of sporulating cells was at least two times higher than that of glucose. When starch was used as the carbon source, the growth rate was reduced; sporulation occurred, and the end products and carbon distribution were similar. Alcohol dehydrogenase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase were preferentially formed by sporulating cells. In vegetative cells, the formation of these enzymes was repressed if the glucose concentration in the medium was increased. The change in enzyme activity appeared to be related to a morphological change in the cells and indicated an altered metabolic pattern for sporulating cells.

Production and catabolite repression of the constitutive polygalacturonic acid trans-eliminase of Aeromonas liquefaciens.

Production of polygalacturonic acid (PGA) trans-eliminase was greatly stimulated under conditions of restricted growth of Aeromonas liquefaciens. This was accomplished either by substrate restriction in a continuous-feeding culture or by restricting divalent cations in a batch culture, with the use of PGA as the sole source of carbon in a chemically defined medium containing inorganic nitrogen. Slow feeding of glucose, glycerol, or PGA to carbon-limited cultures allowed PGA trans-eliminase to be formed at a maximum differential rate 500 times greater than in batch cultures with excess substrate present. The differential rate of enzyme formation obtained by slow feeding of these three substrances or of a mixture of PGA plus glucose was observed to be the same. Therefore, PGA trans-eliminase produced by A. liquefaciens, contrary to the current view, appears to be constitutive. These observations also indicate that production of PGA trans-eliminase is subject to catabolite repression and that limiting the substrate reverses this repression. It was also found that, under conditions of unrestricted growth, any compound which the bacteria can use as a source of carbon and energy repressed constitutive PGA trans-eliminase production. The heritable reversal of catabolite repression of PGA trans-eliminase synthesis was demonstrated by isolation of mutant strain Gc-6 which can readily synthesize the constitutive catabolic enzyme PGA trans-eliminase while growing in the presence of excess substrate.

Natural selection and feeding speed in a blood-sucking insect

When a blood-sucking insect 'bites’ a sensitized host it must, if it is to survive, depart before the host is alerted by the irritation that accompanies or precedes the 'immediate’ reaction. There is a safety period between initial salivary injection by the insect and onset of irritation in the host during which the insect’s meal must be completed; immunity from attack by the host must, therefore, depend partly on the speed at which the insect can tap the blood supply and complete its meal, and partly on an adequate delay in the onset of irritation in the host. In mosquitoes, and other insects that depend on a blood meal for egg production, only those that complete the meal within the safety period can lay a full complement of eggs; the others will either be killed or injured by the host before egg development begins, or they will be disturbed before completion of the meal and so lay fewer eggs. Thus, fast feeders and those producing a delay in the onset of irritation will tend to lay more eggs, and these two properties will be maintained by natural selection, with the onset of irritation in the host acting as the main selection force. Experiments were made comparing a population of wild mosquitoes ( Aëdes africanus ) with that of a colonized species ( A. aegypti ), which had been protected from retaliatory action by the host during the previous 3 years. They showed that while the period between salivary injection and the onset of irritation was the same in both species ( ca . 3 min), feeding was usually fast in the wild species, which had presumably been subjected to rigorous selection against slow feeding, but variable and often slow in the captive species, which had been reared for generations in the absence of this pressure. The results also indicated a slight compensatory delay in the onset of irritation following slow feeding in the wild mosquitoes; presumably a difference in antigenic properties of the saliva affects the speed at which the insect can take up blood, and provides what appears to be a remarkable alternative path way to successful feeding, and so to maximum egg output and thus to survival.

An Automatic Watering Device for Small Potted Plants

SummaryA simple apparatus is described in which the weight of a pot and plant controls a slow water feed so as to maintain constant weight automatically. It can be arranged in a format suitable for maintaining good growth of small plants in small chambers and enabling water consumption to be measured.

Characteristics of the vegetative growth of Bacillus popilliae.

Growth characteristics of the insect pathogen, Bacillus popilliae Dutky, were studied by propagation in shaken flasks and in 2-liter fermentors. Maximal populations between 5 x 10(8) and 2 x 10(9) viable cells per milliliter of culture medium routinely were obtained in incubation periods of 18 to 24 hr at 30 C in a medium composed of 1.5% yeast extract, 0.6% K(2)HPO(4), and 0.2% glucose or trehalose. The carbohydrate required for growth in liquid media was fermented with the formation of 2 meq of acid per mmole of carbohydrate utilized; acid products ordinarily were not subsequently metabolized. B. popilliae is an aerobe, and the amount of growth obtained varied with aeration to an optimum at oxygen absorption rates of about 0.5. Maximal populations persist in a culture for periods of only 1 to 4 hr; cessation of growth was followed immediately by rapid death of cultures, so that less than 1% of the cells remained viable after 48 hr, and viability often was lost entirely by the end of 72 hr of incubation. No cytological evidence for spore formation was observed under any growth condition. Death was not associated with lysis of the cells, although extensive granulation ultimately occurred. Continuous neutralizaiton, augmented buffering, various techniques of dialysis, or slow feeding of the carbohydrate did not markedly alleviate the characteristic death of the cultures.

Pilot plant glycerol production with a slow-feed osmophilic yeast fermentation.

A slow feed batch fermentation is described for the production of glycerol from sugar. The conversion efficiency was approximately 1 mole of glycerol produced per mole of glucose utilized after the cell growth phase. The glycerol production phase was extended several-fold by periodic glucose addition. The yeast cell count remained constant during this time as limited by phosphate, a deficiency required for an efficient glycerol fermentation. A small amount of phosphate was supplied during the extended fermentation, maintaining an active culture, by the normal autolysis of spent cells. Interfering or inhibitory by-products did not accumulate, and the osmophilic yeasts are tolerant of high glycerol concentrations. These factors combined to allow a particularly efficient fermentation well suited to product enrichment by supplying large quantities of substrate over an extended period.

Pilot Plant Glycerol Production with a Slow-Feed Osmophilic Yeast Fermentation

A slow feed batch fermentation is described for the production of glycerol from sugar. The conversion efficiency was approximately 1 mole of glycerol produced per mole of glucose utilized after the cell growth phase. The glycerol production phase was extended several-fold by periodic glucose addition. The yeast cell count remained constant during this time as limited by phosphate, a deficiency required for an efficient glycerol fermentation. A small amount of phosphate was supplied during the extended fermentation, maintaining an active culture, by the normal autolysis of spent cells. Interfering or inhibitory by-products did not accumulate, and the osmophilic yeasts are tolerant of high glycerol concentrations. These factors combined to allow a particularly efficient fermentation well suited to product enrichment by supplying large quantities of substrate over an extended period.

Characteristics of the Vegetative Growth of Bacillus popilliae

Growth characteristics of the insect pathogen, Bacillus popilliae Dutky, were studied by propagation in shaken flasks and in 2-liter fermentors. Maximal populations between 5 x 10(8) and 2 x 10(9) viable cells per milliliter of culture medium routinely were obtained in incubation periods of 18 to 24 hr at 30 C in a medium composed of 1.5% yeast extract, 0.6% K(2)HPO(4), and 0.2% glucose or trehalose. The carbohydrate required for growth in liquid media was fermented with the formation of 2 meq of acid per mmole of carbohydrate utilized; acid products ordinarily were not subsequently metabolized. B. popilliae is an aerobe, and the amount of growth obtained varied with aeration to an optimum at oxygen absorption rates of about 0.5. Maximal populations persist in a culture for periods of only 1 to 4 hr; cessation of growth was followed immediately by rapid death of cultures, so that less than 1% of the cells remained viable after 48 hr, and viability often was lost entirely by the end of 72 hr of incubation. No cytological evidence for spore formation was observed under any growth condition. Death was not associated with lysis of the cells, although extensive granulation ultimately occurred. Continuous neutralizaiton, augmented buffering, various techniques of dialysis, or slow feeding of the carbohydrate did not markedly alleviate the characteristic death of the cultures.

The Mid-Gut Epithelium of the Tick Haemaphysalis Spinigera Neumann 18971

The mid-gut of Haemaphysalis Spinigera consists of a median stomach and diverticulae which are similar histologically. The histological and histochemical appearance of the mid-gut epithelium varies with the age and physiological condition of the tick. In feeding females, and to a lesser extent in feeding males, there is a multiplication and budding-off of epithelial cells. Though there is multiplication of epithelial cells in feeding larvae and nymphs, budding-off of cells was never observed in feeding and metamorphosing nymphs and larvae. During the first phase of slow feeding much of the food material taken in is tissue fluid.

FREE-CHOICE FEEDING OF TROLENE FOR REDUCTION OF CATTLE WARBLE INFESTATIONS (OESTRIDAE: DIPTERA)

The systemic insecticide Trolene reduced the numbers of cattle grubs by 83 to 95 per cent when total doses of 180 and 250 mg. per kg. of animal weight were fed to calves in supplementary feed at daily doses of 10 and 15 mg. per kg. These reductions were significantly greater than those produced by lower daily or total doses including Trolene boluses at 105 mg. per kg. However, very high grub infestations survived in individual animals in all test groups except the two highest dosage groups. This is attributed to variation in feeding behaviour that resulted in the slower feeding animals receiving low doses of insecticide. This factor is apparently an inherent flaw in treatments based on free-choice feeding.Grubs were not eradicated by any of the test treatments and only the 250 mg. per kg. total dosage reduced them below the level of infestation annually observed in two semi-isolated, untreated herds. Studies of the significance of this level of survival in the perpetuation of the treated infestations are necessary.Transitory toxicity-symptoms were observed in the bolus-treated calves but not in the feed-treated calves.

The use of cereal-thickened formulas topromote maternal nursing

W HEN complemental bottle feedings are given in conjunction with maternal nursing to compensate for deficits in the supply of mother's milk, infants soon acquire an increasing willingness to take the bottle at the expense of a corresponding decline in the vigor with which they nurse the breast. The resultant continued incomplete drainage of the gland progressively diminishes its production of milk, and i t is owing chiefly to these interrelated factors that complemental bottle feedings favor the early discontinuance of maternal nursing. The consumption of semisolid food in amounts sufficient to compensate for various degrees of inadequacy in the suppty of mother's milk usually does not appreciably diminish the vigor with which infants nurse the breast. Consequently, the use of appropriate semisolid foods to the exclusion of complemental bottle feedings has the distinct advantage of favoring the continuance of maternal nursing. Owing to my desire to encourage breast feeding, I have exploited, throughout a period of years, this special superiority of suitable foods of moderately thick consistency over liquid milk mixtures. This report presents observations on a selected group of fifty-one infants (twenty-three males and twenty-eight females) whose records exemplify my general experience with this special method of feeding. Each of these infants nursed throughout a period of eight months but consistently failed to obtain mother's milk in adequate quantities. Instead of complemental bottle feedings, these babies received a moderately thick preparation composed of farina or oatmeal cooked in equal parts of whole cow's milk and water with 5 per cent cane sugar and a pinch of table salt added to the mixture. This complemental feeding was started routinely on the third day of life, and it was given by spoon in amounts that were varied in accordance with individual desire and need for additional food. As customarily occurs during initial spoon feedings, these .young infants used the tongue-to push the semisolid mixture forward out of the mouth, but in a comparatively few days this reflex was replaced by a more mature act of swallowing. After this adjustment was made the babies soon displayed a distinct preference for rapid rather than for slow spoon feeding. The policy 'of starting this method of feeding the third day of life had the advantage of acquainting the infants and their mothers with the procedure before they left the hospital. This brief experience gave the

An electromagnetic separator for mineral powders

The separator here described was designed by the author some years ago in order to avoid the tedious process of hand-picking mineral powders in front of an electromagnet. It is a complete machine dealing on a laboratory scale with the less magnetic minerals, such as monazite. For research it is essential that the separation should be clean cut ; in the present case a 90% separation of glauconite from monazite can be made in a single pass, while the removal of more widely differing minerals is complete. The machine must also deal with small samples down to 0.5 gram without loss; this necessitates a small scale and slow feed ; the time required for more bulky samples is consequently rather long, but little or no attention is required during operation. Finally, all the moving parts should be of metal and easily cleaned.