Influence of photoperiods on the growth rate and biomass productivity of green microalgae

The effect of different photoperiods: 24 h illumination and a 12:12-h light/dark (12L:12D) cycle on the growth rate and biomass productivity was studied in five algal species: Neochloris conjuncta, Neochloris terrestris, Neochloris texensis, Botryococcus braunii and Scenedesmus obliquus. The green microalgae examined differ in the reproduction mode. Continuous illumination stimulated the growth of B. braunii and S. obliquus more effectively than the growth of the microalgal species from the genus Neochloris. However, under shorter duration of light of the same intensity (12L:12D cycle), the growth of all the three species of Neochloris was stimulated. Under continuous illumination, the specific growth rate in the first phase of B. braunii and S. obliquus cultures was higher than the growth rate of Neochloris, whereas under the 12L:12D cycle, the specific growth rate of all the three Neochloris species was generally higher than that in B. braunii and S. obliquus. As a result, the light regime influenced algal biomass productivity differently. The maximum biomass productivity was obtained in B. braunii and S. obliquus cultures carried out at continuous illumination. All the Neochloris species produced biomass more efficiently at the 12L:12D cycle, which was two–threefold higher than that of B. braunii and S. obliquus. The unicellular species of the green microalgae from the genus Neochloris, examined for the first time in this study, are promising prospective objects for algal biotechnology.     

Influence of the growth rate calculation on the relationship between growth rate and temperature

Three calculations of the growth rate (e.g. slope of a plot of the log10 of cfu ml-1 vs time, mum of the Gompertz equation and the reciprocal of time to obtain 108 cfu ml-1) were compared for Escherichia coli TG1 growing in tryptone soy broth medium at temperatures ranging from 14 to 39 degrees C. Up to now, the influence of using such different definitions on the relationship between microbial growth rate and temperature has never been investigated. In order to compare these calculation procedures, a dimensionless analysis based on the following normalized variables, mudim = mu/muopt and Tdim = [T-Tmin]/[Topt-Tmin], was used (Dantigny 1998). The influence of suboptimal temperatures on the growth rate was represented by means of a Belehràdek-type model based on a power function law: [mudim] = [Tdim]alpha. The influence of the different growth rate calculations on the model constants was assessed. Despite the great dependence of the raw growth rate values on the calculation procedure, the dimensionless analysis demonstrated that the alpha-value is independent of the growth rate definition. This result suggests that any definition for the growth rate can be utilized in studies aimed at determining the influence of temperature on microbial growth and highlights the interest of using dimensionless variables to overcome differences in the order of magnitude of the growth rate data and to avoid confusion between definitions.     

Interrelation between thrombin structure and its stability

Temperature inactivation of human thrombin has been studied when finding out the mechanism of this enzyme stabilization by amino acids. Effect of a number of amino acids on thrombin in the conditions (pH) of the highest activity of proteinase has been investigated. It is established that most amino acids are characterized to more or less extent by the protective action, when hampering the temperature inactivation of the enzyme. The correspondence was mainly found between the stabilizing effect of amino acids and thrombin specificity. Thrombin is stabilized by L-arginine and DL-lysine more intensively than by other amino acids. A stabilizing effect of L-glutamic acid was shown in contrast to the action of the latter on trypsin that was obviously connected with the original structure of the active centre of thrombin, that is the availability of anionic binding centre which includes Lys68, Arg72, Arg77. High thrombin stabilization by such amino acids as phenylalanine, DL-serine, DL-methonine was an exception. It was established that amino acids stabilize thrombin with formation of a compound with the reactive centre of its molecule, like the compounds enzyme-substrate. The macrostructure stability probably depends, to a considerable extent, on the state of the enzyme reactive centre: thrombin molecules, which contain a free reactive centre, are more labile than those which reactive centre is bound to the reagent of more or less specific character. The inhibition of the autolysis process may be another manifestation of thrombin stabilization by amino acids.     

Interrelation between thrombin structure and its stability

Data concerning peculiarities of fermentative nature and structure of thrombin in water-salt solution have been generalized; regularities of stabilizing effect made on thrombin by various polyols and other substances have been analyzed. It has been shown that formation of thrombin optimum macrostructure is one of the methods of its stabilization. Presence of different dissolving additives changes this enzymes hydration and this affects its stability and activity. There exist some systems to stabilize thrombin solutions. The systems consist of various salts, low-molecular and high-molecular polyols, surfactants, protein chain, composition buffer, etc. It has been shown that optimal concentrations of polyols, buffer salts and surfactants, as well as protein interaction increase considerably thrombin stability, preserving secondary structure even under its low concentration in the solution.     

Interrelation between long-chain fatty acid oxidation rate and carnitine palmitoyltransferase 1 activity with different isoforms in rat tissues

This study examined the interrelation between the long-chain fatty acid (LCFA) oxidation rate and the carnitine palmitoyltransferase (CPT) 1 activity in various tissues containing L-CPT1 or M-CPT1. The Liver, kidney, heart, white and red gastrocnemius muscles, and white and brown adipose tissues obtained from Sprague-Dawley rats were examined. In the tissues containing L-CPT1 the liver showed a significantly higher (P<0.01) palmitate oxidation rate and CPT1 activity than the kidney. Among the tissues containing M-CPT1, the brown adipose tissue showed the highest palmitate oxidation rate and CPT1 activity. The tissues containing M-CPT1 (r2=0.907, p<0.001) showed a strong positive correlation between the palmitate oxidation rate and the CPT1 activity. The ratios of the palmitate oxidation rate to the CPT1 activity were calculated. The ratio in the liver was highest and the ratio in the kidney was lowest among the tissues. The ratios of the tissues containing M-CPT1 were similar. These results showed that the LCFA oxidation rates in the tissues containing M-CPT1 were directly proportional to the CPT1 activity, but not similarly proportional to the CPT1 activity in the tissues containing L-CPT1. In conclusion, CPT1 activity seems very important factor for LCFA oxidation, but it might be not the only rate-limiting step in LCFA oxidation.     

Relation between growth rate and erythromycin production inStreptomyces erythraeus

Summary The relation between specific growth rate and specific rate of product formation was studied in phosphate-limited chemostat cultures ofStreptomyces erythraeus. Specific rates of formation were measured for both the final product, erythromycin A, and several of its biosynthetic precursors. In all cases rates of formation increased with inereasing growth rate, indicating that antibiotic production was strongly growth-linked.     

The synergism between penicillin and kanamycin

Summary In vitro, a synergism was demonstrated between kanamycin and penicillin against penicillin-sensitive and penicillin-resistantStaphylococcus aureus, and against sixProteus strains. Strains ofE. coli, Klebsiella, Pseudomonas andEnterococcus showed a variable response to the combination of these two antibiotics. On the basis of the results obtained, a number of conclusions were reached with regard to the range of indications for treatment with these combined antibiotics. Indications include infections caused by penicillin-resistantStaphylococcus and urinary infections caused byProteus bacteria. Infections by other bacteria may also constitute an indication, but it is maintained that in vitro determination of resistance is indispensable in all cases. A number of arguments are presented against the use of a quantitatively fixed combination of the two antibiotics.     

The relationship between nutrient feed rate and specific growth rate in fed batch cultures

Summary Equations are described which relate nutrient feed rate to specific microbial growth rate in fed batch culture. Fed batch cultures are classified into three types: 1) those allowing constant specific microbial growth rate, 2) those in which the rate of change of flow rate is constant and 3) those in which the nutrient flow rate is constant. The basic properties of these three types are described.Symbols F medium flow rate, L³ T^–1 - F _o medium flow rate at zero time, L³ T^–1 - g rate of change of flow rate with time, L³ T^–2 - K _v volume constant, being the total cell weight at zero time divided by the product of the yield coefficient and growth-limiting substrate concentration in the feed, L³ - s _r growth limiting substrate concentration in the feed, ML^–3 - V volume of liquid in the growth vessel, L³ - V _f volume of medium fed to the growth vessel, L³ - V _o volume of liquid in the growth vessel at zero time, L³ - X total weight of cells, M - x concentration of cells, ML^–3 - X _g total weight of cells grown, M - X _o total weight of cells at zero time, M - Y yield coefficient, weight of cells grown per unit weight of growth-limiting substrate - specific microbial growth rate, T^–1     

Relationship between glucose utilization and growth rate in Bacillus subtilis

The effect of growth rate on the rate of glucose utilization has been examined with a sporogenic and a weakly sporogenic strain of Bacillus subtilis by means of the continuous culture technique. Cultures were grown aerobically on a mineral salts medium with glucose as the carbon and energy source. During both nitrogen and l-tryptophan limitation, the rate of glucose consumption (milligrams of glucose per hour per milligrams of cells) decreased when the growth rate was decreased. The coupling between the rate of glucose disappearance and the growth rate was estimated as 76 to 86% during nitrogen limitation and as 60 to 78% during tryptophan limitation. Sporulation had no detectable influence on the coupling.     

Interrelation between the analgesic and ulcerogenic action of cysteamine

Interrelationship was studied between the influence of cysteamine on pain threshold and ulcerogenic effect on the duodenum. Cysteamine (350 mg/kg) induced analgesia in mice which was prevented by naloxone (1.5 mg/kg). In rats, cysteamine produced duodenal ulcers with concomitant analgesia. The intensity of ulceration was higher in animals with lower basal pain threshold. The correlation between central and peripheral effects of endogenous opioids in the development of experimental duodenal ulcers is discussed.