Light-Dependency of Growth and Secondary Metabolite Production in the Captive Zooxanthellate Soft Coral Sinularia flexibilis

The branching zooxanthellate soft coral Sinularia flexibillis releases antimicrobial and toxic compounds with potential pharmaceutical importance. As photosynthesis by the symbiotic algae is vital to the host, the light-dependency of the coral, including its specific growth rate (µ day-1) and the physiological response to a range of light intensities (10–1,000 µmol quanta m-2 s-1) was studied for 12 weeks. Although a range of irradiances from 100 to 400 µmol quanta m-2 s-1 was favorable for S. flexibilis, based on chlorophyll content, a light intensity around 100 µmol quanta m-2 s-1 was found to be optimal. The contents of both zooxanthellae and chlorophyll a were highest at 100 µmol quanta m-2 s-1. The specific budding rate showed almost the same pattern as the specific growth rate. The concentration of the terpene flexibilide, produced by this species, increased at high light intensities (200–600 µmol quanta m-2 s-1)

Repeated segregation and energy dissipation in an axially segregated granular bed

Discrete element simulations were used to study the segregation behaviour in a bed of bidisperse granules in a rotating drum. In the final state the large particles ended up in the upper part of the bed near the vertical walls. In order to arrive at this state, the system went through two cycles of structural changes, on top of which fast oscillations were observed between an axially segregated and a somewhat more mixed state. These oscillations were sustained by different angles of repose near the vertical walls and in the middle of the bed. Concomitantly with the structural changes, the system's energy dissipation went through two cycles after which it settled in the state requiring the least work of all traversed states, suggesting that the granular bed strives for minimal dissipation

A multicomponent reaction-diffusion model of a heterogeneously distributed immobilized enzyme

A physical model was derived for the synthesis of the antibiotic cephalexin with an industrial immobilized penicillin G acylase, called Assemblase. In reactions catalyzed by Assemblase, less product and more by-product are formed in comparison with a free-enzyme catalyzed reaction. The model incorporates reaction with a heterogeneous enzyme distribution, electrostatically coupled transport, and pH-dependent dissociation behavior of reactants and is used to obtain insight in the complex interplay between these individual processes leading to the suboptimal conversion. The model was successfully validated with synthesis experiments for conditions ranging from heavily diffusion limited to hardly diffusion limited, including substrate concentrations from 50 to 600 mM, temperatures between 273 and 303 K, and pH values between 6 and 9. During the conversion of the substrates into cephalexin, severe pH gradients inside the biocatalytic particle, which were previously measured by others, were predicted. Physical insight in such intraparticle process dynamics may give important clues for future biocatalyst design. The modular construction of the model may also facilitate its use for other bioconversions with other biocatalyst

Voeding van de plant via het blad

Ook via het blad kunnen aan de plant voedingsstoffen worden toegediend. Van deze wetenschap, die vooral belangrijk is met het oog op een snelle opheffing van voedingstekorten, wordt in de praktijk reeds gebruik gemaakt. De praktische uitvoering van deze mogelijkheid stuit op weinig moeilijkheden, daar de meeste land- en tuinbouwbedrijven tegenwoordig wel over sproeiwerktuigen voor de ziektebestrijding beschikken

Anaerobic bacterial aggregates: Variety and variation

Chemical conversions that are mediated by micro-organisms exhibit, necessarily, an autocatalytic nature. In Chapter I, this point is elaborated, and it is shown that in continuous-flow systems, the maximum specific growth rate of micro—organisms sets an undesirably low limit to the rate at which a bioreactor may be operated. When bacteria can be grown in the form of clumps (called aggregates in this thesis) , it becomes possible to operate a continuous-flow reactor at far higher loadings, as such aggregates are less subjected to wash-out from the reactor, and may be retained with some efficiency. This hold-up or retention of biomass finds its physical basis in the settling characteristics of aggregates. Unfortunately, however, mathematical descriptions for such systems are rather simplistic and unsatisfactory, as knowledge on physical characteristics of aggregates is lacking. The research in this thesis therefore aimed at a description and understanding of the development of bacterial aggregates, with particular emphasis on physical characteristics. As a model process, anaerobic acidification by a mixed bacterial population was studied in a mineral medium with glucose as the growth-limiting carbon and energy source. Chapter Il gives a description and justification of the anaerobic gas-lift reactor (AGLR) used in this research. A start-up routine employing a dilution-rate shift-up ensured the rapid formation of aggregates from freely suspended cells, provided carrier material (sand) was available. Chapter Ill presents more detailed data on the complicated role of carrier material during the first stages of aggregate formation. Chapter IV illustrates the development of aggregates with data from scanning and transmission electronmicroscopy, and from light microscopy. The final type of steady-state aggregate was found to have high cellular densities at its periphery of 1012 cells per milliliter, which occupied 25 % of the local volume. In the centre of large aggregates, however, a pronounced void with a low biomass concentration was observed. The results were summarized in a working hypothesis on aggregate dynamics, involving cellular lysis due to substrate insufficiency. In Chapter V, data are presented on prolonged AGLR operation. Although aggregate formation in itself was accomplished rapidly, the stabilization of reactor operation was delayed to some extent. Rather large aggregates were found initially, but were seen to disappear from the AGLR once substrate became depleted. This loss in retention could be attributed to the loss in specific weight, and the concomitant decrease in settling velocity. After this shift in biomass hold —up, the reactor was operated for a considerable time span under stable conditions. The events during this rearrangement of aggregate characteristics could be explained in terms of the previously developed working hypothesis. In Chapter VI, the previous findings on the development of aggregates are summarized in a mathematical form. A model is presented describing overall reactor characteristics in terms of the dynamic behaviour of individual aggregates. As a result of substrate consumption, aggregates are growing, and thus increase in size. On the other hand, substrate depletion in the centre of large aggregates causes an internal deterioration by cellular lysis. As a result, large aggregates desintegrate into smaller ones. Overall biomass retention was formulated in terms of the settling velocity of individual aggregates. On the basis of these highly mechanistic formulations, retention was found to depend on the dilution rate, but not on the influent substrate concentration. Reactor biomass concentrations exhibited a complex pattern, depending on the choise of the fragmentation pattern. The importance of the result resides in the possiblity to predict reactor biomass concentration and retention without taking recourse to commonly used, but unattractive, assumptions on the absence of bacterial growth and the uniformity of aggregates

Chain length distribution and kinetic characteristics of an enzymatically produced polymer

Non-processive enzymatic polymerization leads to a distribution of polymer chain lengths. A polymerization model was developed to investigate the relation between the extent of this distribution on one hand, and the polymerization start conditions and reaction kinetics on the other hand. The model describes changes in concentration of chains of length n as the result of two elongation reactions: elongation by monomer addition to length n-1 and elongation by monomer addition to length n. Polymerization reactions were assumed to be zero order in monomer concentration and to obey Michaelis-Menten kinetics with respect to polymer concentrations. In addition, the amount of enzyme available for each individual reaction (n n+1) is assumed to be Non-processive enzymatic polymerization leads to a distribution of polymer chain lengths. A polymerization model was developed to investigate the relation between the extent of this distribution on one hand, and the polymerization start conditions and reaction kinetics on the other hand. The model describes changes in concentration of chains of length n as the result of two elongation reactions: elongation by monomer addition to length n-1 and elongation by monomer addition to length n. Polymerization reactions were assumed to be zero order in monomer concentration and to obey Michaelis-Menten kinetics with respect to polymer concentrations. In addition, the amount of enzyme available for each individual reaction (n n+1) is assumed to be proportional to the concentration of polymer substrate of length n. The development of the shape of the chain length distribution was found to be independent of the value of the overall reaction rate constant; only the rate at which these shapes developed was influenced by the 1st-order rate constant. The value of the Michaelis parameter did affect the form of the chain length distribution curve since it affects the reaction order. An increase in reaction order was found to promote widening of the chain length distribution. Differences in kinetic parameters between the subsequent polymerization reactions, if any, were also found to have a large effect on the development of the chain length distribution. An increase in rate constants with chain length entailed a wider distribution; a more narrow distribution would require a decrease in rate constants with chain length.proportional to the concentration of polymer substrate of length n. The development of the shape of the chain length distribution was found to be independent of the value of the overall reaction rate constant; only the rate at which these shapes developed was influenced by the 1st-order rate constant. The value of the Michaelis parameter did affect the form of the chain length distribution curve since it affects the reaction order. An increase in reaction order was found to promote widening of the chain length distribution. Differences in kinetic parameters between the subsequent polymerization reactions, if any, were also found to have a large effect on the development of the chain length distribution. An increase in rate constants with chain length entailed a wider distribution; a more narrow distribution would require a decrease in rate constants with chain length

Flow-dependent growth in the zooxanthellate soft coral Sinularia flexibilis

Growth characteristics of colonies of the branching zooxanthellate octocoral Sinularia flexibilis, with potential pharmaceutical importance, were measured over a range of water velocities. The highest mean specific growth rate (¿ d¿ 1) was found at a flow velocity of 11 cm s¿ 1. An optimal range of water turbulence was found at a Reynold's number of ¿ 10,000, with a minimum thickness of boundary layer for rapid mass transfer. There was a similar dependency on water velocity for the contents of zooxanthellae, chlorophyll a, and protein, indicating that photosynthesis also runs at an optimum rate at 11 cm s¿ 1, thus maximizing coral growth. Moreover, the corals showed morphological responses to the changes in water velocity: increase in the number of protruding branches (buds) in proportion to increased flow and then decrease at higher flows, as well as reduced sizes of the colonies at high velocitie