Use of the Golden Section search method to estimate the parameters of the Monod model employing spread-sheets

An alternative procedure to obtain the parameters of Monod's growth model in batch culture is presented. It is based on the integral kinetic analysis methodology, employs a one-dimensional Golden Section search optimization method and is implemented on a spread-sheet programme. The procedure is discussed in detail and is illustrated by analysis of batch substrate consumption data by an aerobic bacterial consortium.     

Transgenic animals as a tool for studying the effect of the c-myc proto-oncogene on cardiac development

Transgenic animals provide a model system to elucidate the role of specific proteins in development. This model is now being used increasingly in the cardiovascular system to study cardiac growth and differentiation. During cardiac myocyte development a transition occurs from hyperplastic to hypertrophic growth. In the heart the switch from myocyte proliferation to terminal differentiation is synchronous with a decrease in c-myc mRNA abundance. To determine whether c-myc functions to regulate myocyte proliferation and/or differentiation, we examined the in vivo effect of increasing c-myc expression during fetal development and of preventing the decrease in c-myc mRNA expression that normally occurs during myocyte development. The model system used was a strain of transgenic mice exhibiting constitutive expression of c-myc mRNA in cardiac myocytes throughout development. Increased c-myc mRNA expression is associated with both atrial and ventricular enlargement in the transgenic mice. This increase in cardiac mass is secondary to myocyte hyperplasia, with the transgenic hearts containing greater than twice as many myocytes as nontransgenic hearts. The results of this study indicate that constitutive expression of c-myc mRNA in the heart during development results in enhanced hyperplastic growth, and suggest a regulatory role for the c-myc protooncogene in cardiac myogenesis.     

Domains of neuronal heparan sulphate proteoglycans involved in neurite growth on laminin

Summary A single neuronal cell assay of neurite growth was utilized to determine types and domains of neuronal proteoglycans involved in neurite growth on laminin. Perturbations of biosynthesis and processing, enzymatic digestion with specific lyases, and competition with glycosaminoglycan side chains produced complementary data consistent with a molecular model implicating glycosaminoglycan (GAG) residues of heparan sulphate proteoglycans (HSPGs) in neurite growth. The observations suggest that HSPGs promote neurite growth on laminin by bridging between binding domains for HSPGs on laminin and on the neuronal cell surface, and that the bridge is tethered at both ends by noncovalent interactions between the binding domains and GAG side chains. Sulphation of the GAGs of HSPGs appears to be critical to the tethering and/or neurite growth-promoting activity of neuronal HSPGs.     

An electron microscopy study of wall expansion during Candida albicans yeast and mycelial growth using concanavalin A-ferritin labelling of mannoproteins

Depending upon growth temperature, Candida albicans can exhibit two different morphologies, a budding yeast or a mycelium. By studying the distribution of concanavalin A-ferritin particles on the cell wall surface during bud and germ tube formation, we have elucidated the way cell wall extension occurs. Both processes initially require the localized lysis of the wall in order to allow the incorporation of the newly synthesized material. Later on, the cell wall behaves as an elastic structure, allowing extension by an intosusception process and, as a consequence, cell growth.Abbreviation Con A concanavalin A     

Comparison of transforming growth factor β and a human tumour-derived suppressor factor

Summary Serum-free supernatants from the human melanoma cell line G361 contain a factor that can potently suppress the generation of tumouricidal lymphokine-activated killer (LAK) cells in response to interleukin-2. To characterise the suppressive factor of tumour origin we performed a number of physicochemical and functional comparisons with another immunosuppressive protein, transforming growth factor (TGF). The bioactivity of tumour-derived suppressor factor (TDSF), assayed by suppression of LAK cell generation, was unaffected by a reducing agent but lost when denatured with a chaotropic agent. In contrast, TGF was inactivated by reduction but not denaturation. TDSF lost bioactivity in conditions of pH less than 4, whereas TGF showed no loss of activity. The TDSF moiety has an estimated pI of 4.3 and a molecular mass of 69–87 kDa. This differs from published values of pI 9.5, and 25 kDa molecular mass for TGF. Anti-TGF antiserum reversed the effects of TGF but did not affect the suppression of LAK cell generation caused by TDSF. These findings provide compelling evidence that the TDSF moiety is not TGF, and may be a novel immunoregulatory cytokine.     

Growth,maturation and survival in a laboratory-reared Rhabdocoelid Turbellarian,Macrostomum orthostylum (BRAUN 1885)

Growth, maturation and survival of a free living turbellarian Macrostomum orthostylum (BRAUN), from a brackish water fish-farm, were studied in the laboratory under a constant temperature of 24 °C. The worms tolerated a wide range of salinity (1 to 30‰). Maximum growth (total length) of 1000 μm was attained in 56 days with a mean growth rate of 15.7 μm d^-1. Minimum maturation time (7 days) and highest longevity (112 days) were recorded in 9%. salinity. Survival period was considerably longer at lower salinities (1 to 10‰) and showed negative relationship with higher salinities (11 to 30‰).     

Transplant experiments. Growth-limiting factors for diatoms and bluegreen algae in Norwegian lakes

Population densities and total phosphorus concentrations in samples from different lakes of south-eastern Norway were determined. In addition some transplant experiments with dilute phytoplankton populations were carried out. A laboratory batch culture method was used.The diatoms studied may be divided into three ecological groups based on their cell densities and total phosphorus concentrations in the samples. This classification was supported by the experimental results. Cyclotella spp., Asterionella formosa and Tabellaria fenestrata did not grow or had low growth rates above pH 9. Synedra cf. acus and Fragilaria crontonensis had often high growth rates within the pH 9–10 range, but were not able to grow at pH values above 10. High pH-values had no effect on the growth rate of Oscillatoria. Oscillatoria, Synedra and Stephanodiscus were severely growth-limited in filtered water from oligotrophic lakes. Maximum growth rates of all the populations studied were often obtained after addition of phosphate and chelated iron (FeEDTA) in combination to filtered water samples from oligotrophic/mesotrophic lakes.