Tropical Strains Research Articles

Characterization of several tropical strains of Anabaena and Nostoc: Morphological and physiological properties, and plasmid content

Thirty Anabaena and Nostoc strains isolated from West African soils were characterized for their morphological and physiological properties, and surveyed for plasmids. Most strains were found to harbour one to five plasmids whose molecular masses ranged from 1.5 to 120-150 X 10(6) daltons. No relationship between these plasmids and phenotypic properties such as carbon source utilization, antibiotic resistance or cyanophage and toxin production could be established.

N2‐Fixation in Field Beans Quantified by 15N Isotope Dilution. I. Effect of Strains of Rhizobium phaseoli1

AbstractMost soils sown to field beans (Phaseolus vulgaris L.) contain indigenous Rhizobium phaseoli; thus, few studies have evaluated the effect of different strains of R. phaseoli on N2 fixation and yield of bean cultivars. Since western Canadian soils contain no indigenous R phaseoli, strains were screened for their ability to fix N2 in two bean cultivars, Aurora and Kentwood. Initially, the N2‐fixing ability of 19 strains of R phaseoli was determined in vitro. The best were then compared with 16 superior Centro Internacional de Agricultura Tropical strains in a 2‐ year International Bean Inoculation Trial in the field in association with the same two small white bean cultivars. 15N isotope dilution at levels of 15N natural abundance in the field showed the % Ndfa (percentage plant N derived from the atmosphere) averaged 50% for Aurora but only 32% for Kentwood over all 16 strains. The % Ndfa did not vary between the two experimental years, but due to different levels of soil N, yield and actual amounts of N2 fixed did vary. Aurora averaged 70 kg N ha−1 and Kentwood 37 kg N ha−1 fixed. Some strains fixed more than 100 kg N ha−1 in Aurora, resulting in dry matter and N yields in excess of uninoculated treatments receiving 40 or 100 kg fertilizer N ha−1. Strains of R phaseoli from high temperature soils of Latin America fixed high amounts of N2 in association with temperate bean cultivars under conditions of low temperature growth (10 to 23°C). CIAT strains 632,899, 640, and 904 and commercial Nitragin were highly efficient N2 fixers with Aurora as were CIAT strains 952, 161, 166, and commercial Nitragin with Kentwood. Thus, R. phuseoli are as efficient as other rhizobia in supplying fixed N2 to their host plant and, in N2‐fixing mode, certain bean cultivars can meet their genetic yield potential in the field without the addition of fertilizer N.

COMPARATIVE GROWTH OF Isochrysis galbana PARKE AND Isochrysis aff. galbana, CLONE T‐ISO AT POUR TEMPERATURES AND THREE LIGHT INTENSITIES

AbstractThe growth of a temperate and a tropical strain of Isochrysis was studied at four temperatures and three light intensity levels. All algal cultures were grown in an enriched artificial seawater medium under constant illumination and were bubbled with air enriched with 0.1% CO2. Culture density (cells/ml) was measured periodically during exponential growth. Average growth rates for each combination of temperature and light intensity are presented as doublings/day. Observations of growth under the various culture conditions indicate that T‐ISO (tropical strain) grows rapidly over a much broader range of temperatures than does I. galbana. Variations in growth at different light intensity levels suggest that the optimum light level increases as a function of temperature for T‐ISO and that the growth of I. galbana is inhibited by high levels of light (1500 μW/cm2). The relative value of both strains as food for larval and juvenile oysters and the advantages and limitations of large scale culture are discussed.

Nodulation of Acacia Species by Fast- and Slow-Growing Tropical Strains of Rhizobium

Thirteen Acacia species were classified into three groups according to effective nodulation response patterns with fast- and slow-growing tropical strains of Rhizobium. The first group nodulated effectively with slow-growing, cowpea-type Rhizobium strains; the second, with fast-growing Rhizobium strains; and the third, with both fast- and slow-growing Rhizobium strains. The Rhizobium requirements of the Acacia species of the second group were similar to those of Leucaena leucocephala.

The relation between nitrogen percent and dry weight of inoculated legumes

Results of numerous tests of tropical and temperate legume hosts and Rhizobium strains accumulated between 1952 and 1966 were examined for a relation between N percent (y) and dry weight per plant (x). The data fitted the equation y=A−be−cx. The most effective Rhizobium strains can be selected on the basis of dry matter yields of whole plants or plant tops only, without the need for N analyses, using statistical analyses. A previously proposed method which employs the linear relation between N-yield and dry matter yield was shown to apply only when data for strains which are not fully effective are excluded.

Hydrolytic Enzyme Production by Rhizobium

Cellulase and hemicellulase activity was detected in temperate (infective and noninfective) and tropical strains (infective) of Rhizobium. Hydrolytic enzymes were initially detected by a cup-plate assay. The presence of cellulase and hemicellulase was confirmed by viscometric assay. Implications of the presence of these enzymes in Rhizobium are discussed.

Prepatent periods of a tropical strain of Plasmodium vivax after inoculations of tenfold dilutions of sporozoites

Eleven patients requiring malaria therapy were inoculated intradermally with graded doses of sporozoites of the Chesson strain of Plasmodium vivax. Estimated doses of 10 sporozoites were given to four patients, of 100 to three patients, of 1,000 to two patients, and of 10,000 to two patients. Parasitaemia was detected in all patients 12 to 17 days after inoculation; fever began on the 14th to 19th days. The results of the trial are compared with earlier work on a temperate strain of P. vivax in which patients given small doses of sporozoites exhibited long prepatent periods of 257 days or more. It is concluded that the differences in the two strains can be explained by the assumption that, in varying proportions, all strains of P. vivax produce two types of sporozoites, one eliciting short prepatent periods (Type I), and the other lying dormant or developing slowly to give rise to long prepatent periods (Type II). The latter type greatly predominates in temperate strains, but not in tropical strains; at high dilutions, therefore, pure suspensions of Type II sporozoites of temperate strains can be prepared. It is thought that relapses of P. vivax are in reality a delayed parasitaemia arising from Type II sporozoites.

A strain of Plasmodium vivax characterized by prolonged incubation: the effect of numbers of sporozoites on the length of the prepatent period

The North Korean strain of Plasmodium vivax was characterized by its extraordinarily prolonged incubation period in certain circumstances. It was clearly demonstrated by quantitative observations that the phenomenon may be elicited by the inoculation of small numbers of sporozoites. After the intradermal inoculation of 10 or 100 sporozoites, the incubation period was delayed for periods varying between 262 and 628 days; after 1,000 sporozoites, with one exception, the same delay occurred; after 100,000 sporozoites, the incubation period was always of normal duration (13–16 days). Two laboratory-acquired infections in workers who had taken a prophylactic drug showed incubation periods of 315 and 329 days, respectively. Various theories for the phenomenon of prolonged prepatent periods are examined, and the most satisfactory one is based on the presumed existence of two populations of sporozoites in P. vivax. In temperate strains, sporozoites requiring long prepatent periods (LPP) for development are present in great excess over a much smaller proportion of sporozoites characterized by short prepatent periods (SPP); thus small doses will elicit the phenomenon, though doses of over 1,000 sporozoites will mask the effect as the few SPP sporozoites will produce an infection with a normal (i.e. short) prepatent period. In tropical strains, the relative proportions are different, perhaps in equal numbers, and even in small doses some SPP sporozoites will be present and normal prepatent periods should ensue whatever the dosage.

Diapause in a Tropical Strain of the Tobacco Hornworm 1

The population of tobacco hornworms, Manduca sexta (L.), on St. Croix was found in field tests to enter diapause most months of the year, but the insects that fed in December, November, and May diapaused most frequently. Termination of diapause usually occurred in May. When the St. Croix strain of hornworms was reared in the laboratory at several photoperiod-temperature regimens that would have produced a high incidence of diapause in the North Carolina strain, only about 10% diapaused, and no particular stage was responsive to diapause- producing conditions. Photoperiod did not appear to be the prime inducer of diapause.

Observations on Hybridization and Heterosis in Parasitoids of Synanthropic Flies2

Expressions of hybrid vigor were found in F1 through F3 generations of crosses between strains of parasitoids of synanthropic flies from climatically similar but geographically isolated areas. There was an apparent lack of heterosis among progeny of a cross between Tropical and Temperate Zone strains. A practical advantage of utilizing exotic strains from similar climatic areas for the biological control technique of inundation is indicated. Considerations are presented for the possible production of synthetic superior strains through direcled heterosis.

GROWTH AND THE PRODUCTION OF EXTRACELLULAR SUBSTANCES BY TWO STRAINS OF PHAEOCYSTIS POUCHETI1,2

SUMMARYClones of Phaeocystis were isolated from winter surface waters off Woods Hole, Massachusetts, and from the tropical Atlantic near Surinam, South America. Northern strains survived only up to 14 C, while the tropical strain survived only as low as 17 C. Colony shapes of the northern and tropical clones differed somewhat, but the motile and non‐motile single cells of both strains seemed identical in the light microscope. By current taxonomic criteria both strains belong to the species P. poucheti (Hariot) Lagerheim.When growing in the form of colonies, both strains excreted 16–64% of their photoassimilated carbon into the medium, mainly as carbohydrates of varying molecular weights. However, cultures predominantly in the form of single cells released only about 3% of their photoassimilated carbon. The qualitative composition of the carbohydrates released is similar for the 2 strains, consisting of some 8 sugars or sugar derivatives with glucose, mannose, and rhamnose as the dominant components. The production of acrylic acid was confirmed. We estimate that as much as 7 μg/liter of acrylic acid, and at least 0.3 mg/liter of polysaccharides can be liberated in a Phaeocystis bloom.

Multipass drying of paddy (rice) in the humid tropics

Rice is a difficult grain to handle owing to its susceptibility to cracking during drying and breakage during subsequent milling. Using a tropical rice strain this work shows that “multipass” drying of wet paddy (with limited moisture content removal per pass, and a period of tempering between each pass) greatly improves milling head yields. Dryer operating capacity can be almost doubled. The following drying process variables have been found to be statistically significant and interrelated. 1. (a) Number of passes of the paddy through the dryer; 2. (b) Number of hours of tempering in hot storage; 3. (c) Flow rates of air through the grain. Each of these greatly influence dryer and installation design. Suggestions are also made for temporary storage of partially dried paddy as a means of further increasing drying complex capacity.

Leucaena Cytogenetics in Relation to the Breeding of Low Mimosine Lines1

Cytological and biochemical studies were conducted in the genus Leucaena in relation to the breeding of low mimosine, high yielding forage types of L. leucocephala (Lam.) de Wit. Meiotic and mitotic chromosomes were studied in the following species; L. leucocephala and L. pulverulenta (Schlecht) Benth. (2n = 56); L. trichodes Benth., L. lanceolata (S. Wats.), L. stenocarpa (Urban), and accessions designated “L. buitenzorg” (2n = 52) and “L. esculenta” (2n = 104).All species of Leucaena hybridized freely, insofar as they were tested. The 80‐chromosome hybrids of L. pulverulenta ✕ L. leucocephala were grown and studied in detail. Seed recovery and yields of these hybrids were high, despite meiotic chromosome pairing of 26 bivalents and 28 univalents. F2 plants ranged widely in chromosome numbers.Assays for the toxic alkaloid, mimosine, were conducted on F1, F2, and backcross progenies from a cross of high ✕ low mimosine strains of L. leucocephala. Despite the apparent polyploidy of the species, wide variations were observed in mimosine contents of the segregating generations, enabling the selection of plants with less than 30% of the normal mimosine values (ca. 4% dry weight) of tropical forage strains. The correlation between mimosine and protein contents for related F2 segregants from high ✕ low mimosine crosses was not significant (r = .60).

The duration in the human host of infections with a Panama strain of Plasmodium falciparum.

Summary and ConclusionsIn a Panama strain of Plasmodium falciparum 23 inadequately treated infections persisted for an average of 279.5 ± 19.9 days, with a range in duration from 114 to 503 days. Four cases persisted for more than a year. The initial period of continuous parasitemias in 37 cases persisted for an average of 115.7 ± 7.5 days. This was followed in 23 cases by a period of terminal intermittent parasitemias with a mean duration of 168 ± 19.0 days. There was little difference between blood and sporozoite induced infections where duration of the infection was concerned.The results reported extend to a tropical strain the findings of Eyles and Young (1951) on the duration of a temperate zone strain of P. falciparum. The application of these findings to certain field conditions is discussed.The Panama strain of falciparum apparently is somewhat more virulent than the United States strain. Although the maximum parasite densities were similar in the two strains, the Panama strain was nearly double the U. S. strain in the length of initial clinical episode, number of clinical episodes and total hours of fever. Other criteria suggestive of strain difference are the significantly longer duration of terminal intermittent parasitemias in the Panama strain, the absence of cross-immunity between the two strains, and differences in gametocyte morphology.

Present concepts and treatment of plasmodium vivax malaria.

WITHIN the past few years classic concepts of malaria have been modified by the addition of new knowledge. The details on different strains of Plasmodium vivax (benign tertian), discovery of tissue stages of P. vivax and P. falciparum, and discovery of new therapeutic agents have all added to our understanding of malaria and made rational treatment possible. The majority of these changes have come about through controlled tests in human volunteers, following careful preliminary work in animals. The data on various strains of P. vivax have done much to aid our understanding of the relapse pattern of this type of malaria. Coatney and co-workers* have worked out the life pattern of the St. Elizabeth strain, a temperate zone malaria, and of the Chesson strain, a tropical strain originating in the South Pacific. The Figure shows the relapse pattern of these two strains of P. vivax malaria in experimentally induced infections.

STRONGYLOIDES INFECTIONS IN MAN AND ANIMALS IN THE ISTHMIAN CANAL ZONE

From a study of strongyloides infections in man and animals in this region, it has been determined, in confirmation of the view of Grassi, Calmette, and others, that they are not causative factors in the production of diarrhea. The mother worm, however, burrows into the mucosa and deposits her ova there. Certain tissue reactions take place and are evidenced by the cellular proliferation in those portions of the intestines occupied by the nematodes. In animals, there is an associated anemia, not positively attributable to the strongyloides, but, on the other hand, not attributable to any other cause. It is possible that S. stercoralis may cause some degree of anemia in man. The amount is indeterminable in this region among hospital cases on account of the associated hookworm disease or malaria. Portals of entry for various microörganisms are made by the female mother worm and her larvae in the small intestine, and, while no case of general bacterial infection has been proved to have arisen in this way, its occurrence is possible and highly probable. In the cultures of strongyloides of man, there is among natives, who presumably are infected with purely tropical strains, a very marked predominance of development by the indirect or sexually differentiated mode, in some cases, an absolutely pure culture of the indirect mode larvae being obtained. There are, however, natives, cultures from whose stools contain from a single filariform larva of the direct phase up to a very definite predominance of this mode. Cultures from natives of the temperate zones contain a marked predominance of the direct phase larvae. The presence of the filariform (direct mode), larva is perhaps best accounted for by its being an attempt at more perfect parasitism (Stiles). From a correlation of culture study with the results of a histological examination of the invaded mucosa, this explanation of the derivation of the two phases is suggested. The mother worm in the intestinal tract has two kinds of progeny: (a) those expelled into the crypts or lumen, and (b) those imbedded in the intestinal wall. One lot becomes larvae of either the direct or indirect phase; the other lot of the opposite phase. It appears to me that the intraepithelial cell-developed larvae furnish the direct phase, while the embryos expelled directly from the mother become the indirect phase larvae. This will require for its confirmation a study of cultures in connection with a histological examination of the infected intestinal wall. Cold merely inhibits the development of the larvgammaaelig; into either the filariform (direct) or into the sexually differentiated adults, and does not alter the anlage. The resistant as well as the infecting form is the filariform larva, and all chemical larvicides must be directed against this form. Thymol and an alkaline cresol resin soap were found to be effective larvicides for the filariform larvae. Two new strongyloides of the monkey and ant bear are described. Cultures of these nematodes show a predominance of the indirect mode of development.