Intraguild predation: The dynamics of complex trophic interactions

There is a long-standing debate in ecology concerning the relative importance of competition and predation in determining community structure. Recently, a novel twist has been added with the growing recognition that potentially competing species are often engaged in predator-prey interactions. This blend of competition and predation is called intraguild predation (IGP). The study of IGP will lead to a reconsideration of many classical topics, such as niche shifts, species exclusion and cascading interactions in food webs. Theoretical models suggest that a variety of alternative stable states are likely in IGP systems, and that intermediate predators should tend to be superior in exploitative competition. Many field studies support these expectations. IGP is also important in applied ecological problems, such as the conservation of endangered species and fisheries management.     

Solvent effects on biocatalysis in organic systems: equilibrium position and rates of lipase catalyzed esterification

Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.     

Kinetic studies and unstructured models of lymphocyte metabolism in fed-batch culture

The growth of two lymphocyte cell lines, a hybridoma cell line and a human cutaneous T cell lymphoma (HuT78), was studied in fed-batch culture, and unstructured models of growth developed. A criteria was established to insure that the growth rate varied by less than a specified tolerance throughout the culture period. Glutamine and serum were growth-limiting nutrients for both cell lines with half-maximal growth rates at 0. 53 mM glutamine and 0. 55%(v/v) serum for the hybridoma cells and 0. 21 mM glutamine and 1. 5% serum for the HuT-78 cells. Over the range of glucose concentrations from 5. 5 mM to 28 mM, the specific growth rate of hybridoma cells was independent of glucose concentration, whereas glucose concentrations above 5. 5 mM inhibited HuT-78 growth. For both cell lines, the growth rate was significantly inhibited by the addition of ammonium, although the hybridoma cell line was more affected by ammonia than was the HuT-78 cell line. Growth of HuT-78 cells increased in the presence of interleukin-2. Unstructured models for the hybridoma cells were similar to other models presented in the literature. Applications of these models to adoptive immunotherapy are discussed.     

The capybara (Hydrochoerus hydrochaeris) as a reservoir host for Trypanosoma evansi

Discovery of two ill horses and three dogs naturally infected with Trypanosoma evansi near an experimental station in the Eastern Plains of Colombia led to a search for reservoir hosts of the parasite. Infection was detected in 8/33 healthy capybaras (Hydrochoerus hydrochaeris), none of the remaining 14 horses, and none of 32 Zebu cattle (Bos indicus), 18 paca (Cuniculus paca) and 20 spiny rats (Proechimys sp.). Contrary to common opinion, the results indicated a carrier state in the capybara. Diagnosis was based on morphology, behaviour in albino rats, and pathogenicity and host range in domestic animals.